The Bulletin of the Canadian Association of Physicists

Volume 26, No. 3 May I, 1970

U

Bulletin de l'Association canadienne des physiciens

La Physiq Volume 26, No. 3 1er mai 1970

Two things you can expect from Ortec true coax Ge(Li) detectors:

Maximum timing accuracy over the widest dynamic range,

Tteinj Spectra 100 keV to ! M e *

Spectrum obtained with ORTEC True Right Cir-cu l a r C y l i n d e r Ge(L i ) 8.9% deiector. Calibra-tion 0.448 nsec/channel

Spectrum obtained with trapezoidal Ge( l i ) 4% d e t e c t o r ( t y p i c a l fo r wrap-around coax). Cali-b r a t i o n 1 .04 n s e c / channel

C H A N N E L S

For studies of angular correlation, positron annihilation, gamma decay schemes, and similar experiments where timing accuracy is crit ical, the true coaxial Ge(Li) crystal is the detector of choice

Unlike trapezoidal and wrap-around coax con-figurations, charge col lect ion distances for the true coax are independent of the location of interaction of the impinging particle. Thus timing inaccuracies are minimized, even for much more efficient detectors.

The benefits: time distribution of detected events is more nearly Gaussian Low energy tail ing is eliminated. Experi-ments can be run over a wider dynamic range without timing distortion. A tim- /JRFl! ing window as wide as 2» remains / 1 f r ~ acceptably narrow.

One of the problems normally

and off-the-shelf delivery.

associated with true coax Ge(Li) detectors is delivery: most suppliers will provide them only on special order. We make them on a routine basis. And we have some on our shelf right now. Just tell us what you need; chances are we have it in stock and can tell you its exact measurements.

To learn more on the subject, write for Appli-cation Note No. 31, "Timing with Germanium Detectors." Ortec Incorporated, 107 Midland Road, Oak Ridge, Tenn. 37830. Or call (615) 482-4411. In Europe: Ortec GmbH, 8 Munchen 13, Frankfurter Ring 81. Telephone: (0811 ) 359-1001.

f l P T F H " A I M E O c G C O M P A N Y 4 6 7 8 »

Represented in Canada by

Radionics Ltd., 195 Graveline St., Montreal 376, P.Q., 505 Eglinton Ave. W., Toronto 305, Ont., 376 Churchil l Ave., Ottawa 3, Ont., 3067 Chemin des Quatre-Bourgeois, Quebec 10, P.Q., 2182 W. 12th Avenue, Vancouver 9, B.C. Charles W. Fowler Co. (British Columbia), 845 106th Ave., N.E. Bellevue, Wash. 98004

Books that speak the language of today's physics

CS, Second Ed.

Blanpied

THE LANGUAGE OF MODERN PHYSICS An examination of the conceptual structure and mathematical methods of modern physics, this book provides students in advanced courses with the necessary information to understand the "language" of Twentieth Century physics. The concentration on concepts and methods has led the author to include a condensed presentatidn of traditional classical topics; but, mainly, this is a book on the physics of the last four decades. Each chapter is concluded by a bibliography and by exercises.

August 1970 Fowles

ANALYTICAL MECHAN This book places emphasis on mechanics as a basic subject with further applica-tion in the other branches of physics and applied science. Thoroughly up-to-date, it includes a chapter on celestial mechanics with a section on satellite motion, and an excellent explanation of the special theory of relativity. Each chapter is concluded by problerris listed in order of their difficulty, and worked examples are included within the exposition.

June 1970 Swanson

AN INTRODUCTION TO PHYSICAL FLUID MECHANICS The most complete fundamental textbook in fluid mechanics available for introductory courses. The concepts of mechanical work are logically and rigor-ously developed for simple and for general fluid systems of control volumes. The first half of the book presents the fundamental material; the second deals with the application of these bdsic principles and definitions.

Just Published

Also of Interest Davis

DIFFRACTION GRATING SPECTOGRAPHS

Sinclair I Bell

GAS LASER TECHNOLOGY

Order from your bookstore, or write to:

February 1970

1969

HOLT. RINEHART. WINSTON 833 OXFORD STREET, TORONTO 18, ONTARIO

UNIVERSITY OF WATERLOO

C O R R E S P O N D E N C E P R O G R A M M E

IN

Mathematics, Chemistry and Physics

A P R O G R A M M E of upgrading courses, by correspondence, for elementary and secondary school teachers is offered annually, commencing early in October. The courses are unique in that they are in the form of taped lectures with supplemental material.

The underlisted courses will be offered in 1970-71 :

Chemistry 224 Principles of Chemical Spectroscopy Chemistry 231 Chemical Bonding and Structure Chemistry 337 Biochemistry Chemistry 344 Inorganic Chemistry Mathematics 130 Calculus Mathematics 131 Algebra and Solid Geometry Mathematics 236 Differential Equations Mathematics 239 Introduction to Combinatorics and Optimization Mathematics 307 Combinatorial Geometry Mathematics 334 Numerical Methods Mathematics 352 Optimization Techniques in Operations Research Mathematics 446 History of Mathematics Mathematics 82 Introduction to Algebra Physics 232 Electricity and Magnetism Physics 235 Optics Physics 237 Astronomy I Physics 244 Quantum Physics Physics 332 Electronics Physics 337 Astronomy II Physics 434 Introductory Quantum Mechanics

For application and further information write:

T H E D I R E C T O R , Correspondence Programme, c /o Department of Physics. University of Waterloo, Waterloo, Ontario.

Summer Institute on Solar Terrestrial

Relationships at

Department of Physics University of Calgary

Calgary, Alberta Canada

June 2-5,1970

S P E A K E R S :

1 Dr. W. Ian Axford, Dept. of Applied Physics and Irifo. Science, U. of California, La Jolla, California

2 Dr. Neil T. Davis, Geophysical Institute, College, Alaska

3 Dr. C. De Jager, U. of Utrecht, Utrecht, Netherlands

4 Dr. J^mes A. Van Allen, Dept. of Physics, U. of Iowa, Iowa City, Iowa

The Sumhter Institute contains 16 lectures spread over four days, covering the areas of Solar Physics, Interplanetary Medium, Cosmic Ray Propagation, Magnetosphere and Auroral Zone Phenomena. Specific topics are suitably chosen to provide an integrated program. The institute is open to interested people including graduate students. There are no fees for attending.

For further particulars, including accommoda-tion, write to: Dr. C. J. Bland, Administrative Officer Department of Physics, University of Calgary CALGARY, ALBERTA (CANADA)

GRADUATE POSITIONS IN PHYSICS QUEEN'S UNIVERSITY

KINGSTON, ONTARIO, CANADA

Research and Teaching Assistantships are available to graduate students, both theoretical and experimental, in the fields of solid state physics, nuclear physics, and radio astronomy. Special experimental facilities include: equipment for ultra high vacuum, magnetic resonance, microwave spectroscopy, luminescence studies, low temperature physics, and for electron structure studies of metals by positron annihilation; a 3-MEV Van de GraafF ppsitive-ion accelerator, and use of the MP Tandem at Chalk River; a 60-ft. radio telescope, and use off the 150-ft. radio telescope at Algonquin Park. Financial assistance in a combination of Scholarships pnd Teaching and Research Assistantships is provided in the range $3500 to $5000 per annum.

Letters of application, requests for brochures, and further information should be addressed to P ro fe s so r A. T. S t e w a r t , H e a d , Department of Physics, Queen's University.

Institut de recherche de l'Hydro-Québec

L'Institut de recherche de l 'Hydro-Québec (L'IREQ) est l 'un des centres les plus importants de recherche et d 'essai du monde. Le

plus complet d 'Amér ique du Nord, c 'est aussi le premier en son genre qui soit tota lement indépendant des manufactur iers. Doté de

chercheurs hautement qual i f iés recrutés dans le monde entier, il pos-sède le matériel de recherche le plus moderne qui soit. Tout d 'abord dest inées à répondre aux besoins du Québec et du reste du Canada, ses instal lat ions ont aussi été prévues à l ' intent ion de l 'Amér ique du

Nord en général et de tous les pays qui en feront la demande.

Hydro-Quebec Institute of Research

Hydro-Quebec Institute of Research (IREQ) was conce ived as one of the main centres for electr ical research and test ing in the wor ld. It is the most comprehens ive in North Amer ica, and also the first

major centre of its type on this cont inent independent of manufac-turers. It is staffed by a highly qual i f ied group of research workers

recruited f rom around the wor ld, and equ ipped with the most advanced research tools avai lable. A l though des igned first and

foremost to serve Quebec and the rest of Canada, its faci l i t ies are also based on the needs of North Amer ica in general and its doors

are open to the wor ld at large.

Hydro-Québec Mont rea l , C a n a d a

ADDISON-WESLEY

at the June '70

B O O T H 3 2

C A P - A P S - S M F MEETING

Review copies of mos t of these titles will be avai lable well in ad-vance of t he mee t ing dates . Wr i t e us a t :

Add i son-Wes ley ( C a n a d a ) Limi ted 57 G e r v a i s Dr ive D o n Mills, O n t a r i o

ALONSO AND FINN—Physics BAKER—Modern Physics and Anti-Physics BURNS AND MACDONALD—Physics for Biology and Pre-Medicat Students FRYSHMAN—Problem-Solving in Physical Science: For Non-Science Majors MITCHELL AND MITCHELL—Essentials of Electronics PATTERSON—Introduction to the Theory of Solid State Physics PUGH AND PUGH—Principles of Electricity and Magnetism, Second Edition READ—Physics—A Descriptive Analysis REILLY AND VANDERPYL—Physical Sci-ence: An Interrelated Course

SANDERS—Modern Physical Theory: Spe-cial Relativity and Quantum Physics

SEARS AND ZEMANSKY—University Phy-sics, Fourth Edition

SIMMONS AND GUTTMAN—States, Waves, and Photons: A Modern Introduction to Light

TAYLOR—Programmed Study Aid for Introductory Physics: Part I: Mechanics for Students of Science and Engineering

TAYLOR—Programmed Study Aid for Introductory Physics: Part II: Electricity and Magnetism for Students of Science and Engineering

M.Sc. Program in Physics at Lakehead University

Thunder Bay, Ontario

Appl ica t ions are invited f r o m s tudents seeking admiss ion to the M.Sc. degree p r o g r a m in Physics at L a k e h e a d Univers i ty . C a n d i d a t e s with a B.Sc. ( H o n o u r s ) degree and those w h o hope to qua l i fy fo r the degree b e f o r e Sep tember 1st, 1970 will be cons idered fo r admiss ion. T h e n o r m a l per iod a f t e r comple t ing the degree will be approx ima te ly 16 mon ths . C a n d i d a t e s wi th a genera l degree in Physics may be cons idered f o r admiss ion to the M.Sc. degree a f t e r comple t ing a qua l i fy ing year at L a k e h e a d Univers i ty . T h e D e p a r t m e n t has re-search pro jec ts in exper imen ta l and Theore t i ca l , Solid State and P lasma Physics. Ind iv idua l a t ten-tion to g r a d u a t e s tudents on a personal level, which is n o r m a l l y not possible in larger Uni -versities, is the key f e a t u r e of the depa r tmen t .

G r a d u a t e and T e a c h i n g assis tantships a re avai lable fo r the sui tably qualif ied candida tes . Enqui r i es should be addressed to the Chairman, D e p a r t m e n t of Physics, L a k e h e a d Univers i ty .

Previous applicants are requested to write again.

UNIVERSITY OF TORONTO Toronto, Canada

Department of Physics

Geophysicist

Applications are invited, from persons having several years of academic or equivalent experi-ence, for a senior faculty position in Geo-physics. Fields of interest in the department include seismology, geomagnetism, geochrcn-ology and exploration geophysics. Rank and salary open depending on qualifications and experience. Salary would be fully competitive at any level, including full Professor. The position is open from July 1, 1970, but could begin at a later date. Applications should be addressed to Professor J. M. Daniels, Chair-man, Department of Physics, University of Toronto, Toronto 181, Canada.

The Bulletin of the Canadian Association of Physicists

Volume 26, No. 3, May 1, 1970

Physics in Canada

Bulletin de l'Association canadienne des physiciens

Volume 26, No. 3, 1er m a i 1970

La Physique au Canada

EDITOR: D . E . Brodie

ASSOCIATE EDITOR: J.-L. Meunier EDITORIAL BOARD: P. C. Eastman, G. E. Reesor, H. Morrison

EDITORIAL ADDRESS: Department of Physics, University of Waterloo, Waterloo, Ontario

ADVERTISING Advertising Editor, Physics in Canada, Department of Physics, University of Waterloo. Waterloo, Ontario

Published for the Canadian Association of Physicists by the University of Toronto Press

SUBSCRIPTION RATE: $10.00 per year (7 issues)

SUBSCRIPTIONS AND C H A N G E OF ADDRESS: Canadian Association of Physicists, Suite 903, 151 Slater St., Ottawa 4, Ontario. Phone 613-237-3392.

(c) Canadian Association of Physicists/iAssociation canadienne

Editorial - A Crisis for Physicists in Canada? by D. E. Brodie 56

Letter to the Editor 56

Température critique pour la supraconductivité by ]. P. Carbolic 57

Report on the Second Annual Meeting of the Corporate Members by D. E. Brodie 65

Research in Physics at the University of Saskatchewan. Saskatoon by Henry S. Caplan 68

Pictorial Facteria by Howard O'Brian 72

News/Nouvelles 72

Canadian Physicists/Physiciens canadiens 74

CAP Affairs/Affaires de 1'ACP 74

Calendar/Calendrier 77

Book Reviews 77

des physiciens 1970. All rights reserved

E D I T O R I A L

A Crisis for Physicists in Canada?

Many professors are advising any prospective grad-uate student that they will be happy to supervise his graduate studies, but they also warn the student that he will probably not be able to find employment when he finishes his degree! What can be done to correct Canada's present inefficient use of some of its highly qualified manpower? Many of us are aware of examples of top graduates in physics, or a closely related field, unable to find employment in Canada right now! Contrary to impressions being offered by critics of modern societies, technological development in itself is not a bad thing: the fault in today's societies would appear to be the lack of complemen-tary research and understanding in the area of socio-scientific matters and the lack of concern for the social and ecological effects of new technology. Future research teams must include scientists, engi-neers, biologists, social scientists, etc., to ensure that new technology integrates satisfactorily and safely into society.

Physicists, through the CAP, have recognized the need for an improved understanding of socio-scientific matters and have made an attempt to launch a study of a related problem, but unfortunately monies are required to do it. So far, no sources of funds have been found in either the public or private sector that would enable a study in depth to be carried out. See, for example, the article by R. McNarry in this bulletin and one by M. P. Bachynski in the February issue of Science Forum.

Continuing research and hence technological devel-opment is highly desirable if not essential for an in-dustrialized nation's healthy growth and long-term economic stability. If a nation or an industry has any plans to become a leader, at least in some areas, then it cannot rely solely on adaptation and imitation, no matter how inviting the short-term gains of this ap-proach may appear. Even if this were general policy, can we expect to continue to receive the technology to do this from our benevolent neighbours and competi-tion? We must not risk it. It may well be that the present high standard of living in Canada, as reflected in the G .N.P . per capita, is due to the export of natural resources rather than to imported R and D, as implied

by J. Lukasiewicz in his article in the February issue of Science Forum.

The entire problem is multi-sided and we need a Sci-ence Pol cy soon which will ensure the useful employ-ment of our highly trained people immediately and thus begin to build the base of future industries that will be able to compensate for future depleted natural resourcejs.

IIow best can CAP. channel the views of the physics commur ity in this respect? A first step was taken by consulting the CAP Membership for the preparation of a brief submitted to the Senate Committee on Sci-ence Policy; a second step was taken by establishing a CAP Standing Committee on Science Policy. More information concerning this Committee is available in the March, 1970, issue of Physics in Canada in an ar-ticle reported by M. P. Bachynski. Other relevant facts are available in the O.E.C.D. report, and this report was reviewed in the January issue of Physics in Canada by A. B. Bhatia.

What are your views on this important problem, and what action do you suggest?

D. E. BRODIE

Letter to the Editor

D e a r Sir, T h e recent es tabl ishment of the CAP Commi t t ee on Science Policy, whose objectives and accompl i shments to da te [were out l ined in an art icle by Dr . M. P. Bachyn-ski in the J a n u a r y issue of Physics in Canada, repre-sents, I, feel, a wor thwhi le initiative. T h e Commi t t ee ' s objectivfes are highly commendab le , a l though they will be very difficult to achieve.

Of par t icular interest t o myself , and n o d o u b t t o m a n y others , was the list of "Cri ter ia fo r Appraisa l of M a j o r Scientific Projec ts" proposed by the Commi t t ee . I agree tha t if the Commi t t ee wishes to obtain a con-sensus f r o m the physics c o m m u n i t y on specific m a j o r scientific projects , some clear-cut guidelines fo r dis-cussions mus t be established.

While 1 believe that the proposed "Cr i t e r i a" can be used as a start ing point in coming to grips with the very complex problem of arr iving at a consensus on priori-ties, Dr. Bachynski presents them as "a f r a m e w o r k upon which m a j o r projects can in f u t u r e be discussed objectively". If I accept this s ta tement a t face value, 1 cannot | agree with it.

T o begin with the proposed "Cr i t e r i a" are not cri-teria ih the usual sense of the word , i.e. s tandards o r principles, a thing is judged by. This point would no t be tod serious if real criteria were not to fol low; bu t hopefii l ly they are. F o r example, one of the "Cr i t e r i a" proposed by the Commi t t ee is: "Does the project affect

La Physique au Canada / 57

the balance between little and big science?". This ques-tion is important , but it is not a criterion. However, in answering it, and a t tempt ing to assess the relevance of the answer, we might arrive at a true criterion, possibly of the f o r m : "The expendi ture on big science in Can-ada over the next decade should optimally be between x % and Y% of the gross expenditure on research and deve lopment . " It is positive statements of this type which fit the usual meaning of the word criteria, and which are badly needed.

I also feel that "... discussed object ively" was an un-for tuna te choice of words. I suggest that a much better choice would have been "... discussed rationally". I raise this point, not for the sake of nicety, but because I feel very strongly that we must recognize clearly the very important role that opinions, i.e. subjectivity, must play in discussions and decisions on research priorities. While facts and figures should replace opinions wher-ever and whenever it is both possible and appropriate , the real problem is to provide a f ramework for a ra-tional discussion of the subjective elements which go into research priority determinat ion.

More important , however, than the above questions of semantics is the fact that Dr. B-.ichynski's s tatement conveys, at least to me. the message: "Here is a f rame-work for the discussion of ma jo r scientific projects. N o w we can begin discussing them." Bearing in mind that the object of the discussion is to obtain some feel-ing for priorities, I would suggest that the message should have been: "Here is a list of important questions concerning ma jo r projects. N o w we can begin (o work out a suitable f r amework for discussion." In other words, while I believe that the "Cri ter ia" include many of the essential building blocks for a f r amework , I do not believe that these have yet been assembled to form an appropr ia te f r amework .

T o be useful, the f ramework must serve as a tool fo r guiding the discussion f rom the innumerable questions of detail to the single goal of priorities. This automati -cally suggests a pyramidal a r rangement , with the few really important , but complex questions at the top, and the many more detailed, but individually less important questions near the bot tom. The pyramid must have a vertical and horizontal s tructure which shows as clearly as possible the interrelationships between the various questions, and how the answers to the smaller questions of detail can be grouped to provide answers to the more important ones above.

F o r instance since the question of priorities is one of weighing up costs vs. merits, I would place the two questions "Wha t are the merits of the project?" and " W h a t is the expected cost of the project?" at the top of the pyramid. The fo rmer question is, as usual, the most difficult one to answer, and it will require the most attention. On the merit side of the pyramid, I suggest that the next step is to break down the general question into the two sub-questions "Wha t is the rele-vance of the project and its part icular ob jec t ive(s ) , to national objectives, taking into account the order of priority of the lat ter?" and "What is the probability of the project at taining its part icular ob jec t ive(s )?" These in turn can be subdivided, the fo rmer into separate

questions on national objectives, their priority order at the present time, the particular objectives of the project etc. and the latter into separate questions on the capa-bility of the participants, the scientific feasibility of the proposal, the support to be expected f rom the organiza-t i o n s) in which the project will be carried out . and so on. Ideally, if we wish to arrive at a single figure of meri t for a project, criteria and related value scales should be established for the replies to all of these questions.

The CAP Commit tee might not agree with this partic-ular analysis of the problem, but I am convinced that a s tructured f ramework of this type will be essential if the Commit tee is to make much progress towards the question of priorities.

Whatever the approach used, the task will be diffi-cult. There are many, mostly scientists, who feel in fact that the task of obtaining a consensus f rom the scientific communi ty on priorities in science is impossible. On the other hand, there are also many, mostly non-scien-tists (e.g. politicians) who demand that a consensus should be obtained before any decision is made . I per-sonally believe that if the CAP Science Policy Commit tee manages to reduce for fu ture decisions on ma jo r scien-tific projects, the amoun t of confusion which has ac-companied many in the past, even by a modest amount , its work will have been worthwhile.

I am not sure that this letter will prove to be of assis-tance to the Commit tee in this endeavour , but this was my intent in writing it.

.R.R. K E Y S T O N ,

National Research Council of Canada

Température critique pour

la supraconductivité

A température suffisamment basse, bien des métaux connaissent une transition de phase vers un nouvel état supraconducteur. Comme le titre le suggère, les propriétés électroniques dans cette phase sont très différentes de celles de la phase à température nor-male. Par exemple, au-dessus de la température cri-tique (T,.), le passage d'un courant électrique est toujours accompagné par quelque effet Joule. Par contre, au-dessous de T,., le courant circule sans aucune perte d'énergie.

Une autre manifestation surprenante de la phase supraconductrice est que les propriétés magnétiques changent radicalement lors de la transition. Dans l'état normal, les métaux auxquels nous allons nous in-téresser n'ont pas de propriétés magnétiques impor-tantes. Le faible paramagnétisme de Pauli, ainsi que le diamagnétisme de Landau, peuvent raisonnable-

58 / Physics in Canada

ment être ignorés. A la condensation, un tel métal devient parfaitement diamagnétique; s'il est placé dans un champ magnétique extérieur constant (H), alors la polarisation magnétique (M) à l'intérieur de l'échantillon croît de façon à s'opposer et à annuler exactement le champ extérieur H, de façon à ce que le flux net (B) à l'intérieur soit zéro (B = 0) .

En raison de ce comportement anormal il est de quelque intérêt de comprendre la nature de l'état supraconducteur; d'un point de vue pratique, c'est aussi très important. Par exemple les aimants supra-conducteurs, générateurs de champ de haute inten-sité, sont maintenant utilisés couramment. Les pro-blèmes de refroidissements, qui deviennent critiques dans les aimants de construction conventionnelle, sont complètements éliminés. Les aimants supracon-ducteurs ont, bien sûr, le désavantage de devoir être utilisé à basse température (<T, . ) . Des métaux de haute température critique sont donc à rechercher. En trouver de nouveaux avec des températures T c

plus hautes que celles déjà connues reste un pro-blème d'actualité et de très rares progrès ont été ac-complis car les expérimentateurs sont très peu guidés du fait d'une théorie inexistante.

Avant d'exposer quels sont les paramètres d'un métal contrôlant directement la grandeur de Tc, je voudrais rappeler quelques résultats expérimentaux à ce sujet. Si l'on cherche à savoir quel est l'ordre de grandeur caractéristique de T,., il n'est pas possible de donner une réponse définitive, en raison des va-riations considérables d'un métal à l'autre. Dans Al, T, = 1.2 °K, alors que pour Pb, T(. = 7.2 °K. Des alliages complexes des éléments de transitions mon-trent, d'autre part, des températures Tc beaucoup plus grandes. Par exemple pour Nb:tSn, TP 18 °K. Par contre Na n'a pas été observé dans un état su-praconducteur aux plus basses températures expéri-mentées : une fraction de degré. Dans ce cas la théorie indique que T,. doit être moins de 10~5 °K, c'est à dire pratiquement zéro.

J'espère dans cet article vous faire partager quel-ques-uns des aspects de la compréhension que nous avons au sujet des variations de T0. Cette compré-hension nous est venue comme le résultat de calculs effectués à McMaster durant les 3 dernières années avec quelques-uns de mes étudiants. Je pense que des progrès considérables ont été accomplis, mais je dois cependant vous avertir que ces calculs sont limi-tés aux métaux simples seulement. Par simple je veux dire des métaux dont la structure électronique peut être comprise à partir des idées de la théorie des pseudopotentiels pour l'interaction electron-ion. Ceci

exclut les métaux de transition ainsi que d'autres, tel que le cuivre, métal noble. Dans ces métaux, les elîets de structure de bande peuvent être très com-plexes e ,̂ par conséquent, leur structure électronique n'est pas très bien connue. Empiriquement, c'est pré-cisément parmi ces métaux que l'on trouve les plus grandes valeurs de T,.. Pour attaquer le problême de la recherche de plus grand T„ il est probable que la théorie c]ue je vais exposer devra être étendue aux éléments de transition. Actuellement, ceci est cer-tainement des plus difficile, sinon impossible. Néan-moins, iomme première étape, il semble raisonnable de considérer les métaux simples, particulièrement ceux dont les propriétés électroniques sont bien con-nues et expliquées.

J'ai déjà utilisé trop de termes techniques ! J'aime-rai, au moins pour quelques temps, supposer seule-ment une connaissance générale de mécanique quantique.

Quand les atomes sont assemblés pour former un solide, chaque atome développe un environnement d'état qolide, représentant une perturbation sur les mouvements des électrons atomiques. Dans les mé-taux, cette perturbation est assez forte pour avoir des effets importants sur les orbites électroniques des couches extérieures partiellement remplies. Les cou-ches intérieures complètes sont, d'autre part, très sta-bles; ce que nous avons donc est un ensemble d'ions, à couches complètes, condensés, et formant un réseau périodique. Se propageant à travers ce réseau crys-tallin d'ions, les électrons extérieurs restants forment ce que nous appellerons maintenant le gaz d'élec-trons cle conduction. Ces électrons ont perdu toute possibilité d'être localisés autour d'un ion particulier, commé c'est le cas dans un atome isolé. Au contraire, ils peuvent circuler librement à travers tout le crystal, sans tendance à s'agglomérer autour d'un site parti-culier. Ils doivent alors être considérés comme mem-bres du métal dans son ensemble, par opposition aux électrons attachés aux ions, qui sont donc très locali-sés. Ce sont les électrons de conduction qui seront notre principal sujet d'intérêt. Ils sont les porteurs de chargé sous l'influence d'un champ électrique exté-rieur, èt sont aussi responsables de la supraconducti-vité.

Discutons maintenant de ces électrons de conduc-tion. Si leur propriété la plus importante est leur manque de localisation, on peut, peut-être, essayer de les décrire dans un modèle simple où ils seront considérés comme complètement libres. C'est le mo-dèle de l'électron libre, où toute interaction est ne-gligéei Une telle particule libre sera représentée par

une onde plane, de moment défini p. Pour construire la fonction d'onde du système des N électrons, il est essentiel de ne pas oublier leurs caractères de Fer-mions. A l'exception d'une dégénérescence de spin d'ordre 2, un seul électron peut être dans un état de moment déterminé, p > . Pour obtenir l'état fonda-mental du système, on remplit tout les états de mo-ments, de l'origine jusqu'au niveau de Fermi. Ceci minimise l'énergie. Nous avons donc défini dans l'espace des moments une sphère de rayon kF, ou rayon de Fermi. Chaque état de moment k inférieur à kF est donc occupé et, pour K > kF, l'état est libre. La fonction d'onde, ainsi obtenue, est un simple dé-terminant de Slater construit sur les états d'énergie des électrons les plus bas.

Cette fonction d'onde très simple (une sphère de Fermi libre) est une lère approximation très raison-nable de la fonction d'onde du gaz de conduction. La plupart des propriétés électroniques des métaux peu-vent être comprises, au moins d'une façon qualita-tive, d'après ce modèle. Puisque, comme nous l'avons vu, les propriétés dans la phase supraconductrice sont bien modifiées, ce simple déterminant de Slater ne peut certainement pas être utilisé dans ce cas. Il faut alors passer à la fonction d'onde suggérée par Bardeen, Cooper et Schrieffer1, ou il y a d'importantes corrélations bâties entre paires d'électrons. Je ne décrirai pas ici la nature exacte de ces corrélations de paires, car cela nous entrênerait trop loin. La con-naissance exacte de la fonction d'onde de B.C.s. n'est pas indispensable pour la plupart de ce dont je vais parler.

Notre principal intérêt est de conprendre les inter-actions conduisant à la condensation, plutôt que les détails de cette nouvelle phase. Pour ce qui va suivre, il est suffisant de connaître le résultat de Cooper montrant que, si l'interaction effective entre paires d'électrons au voisinage de la surface de Fermi est attractive, alors la mer de Fermi devient instable pour la formation de paires de Cooper, ce qui con-duit à la supraconductivité. Autrement dit, l'état de plus basse énergie du système des N électrons n'est plus le déterminant de Slater, et l'état lié qui en ré-sulte contient d'importantes corrélations entre paires d'électrons, qui prennent avantage du potentiel at-tractif entre une paire d'électrons. Il est important de réaliser que nous voyons ici une condensation du sys-tème complet des N électrons en une macro-molé-cule. 11 existe alors une énergie d'excitation minimum des électrons, hors de l'état fondamental. C'est le saut A. Plus l'attraction de paire est grande, plus le saut A est important. Une façon équivalente de dire

La Physique au C a n a d a / 59

ceci est : plus l'état fondamental est lié, plus il est difficile de le détruire par agitation thermique, c'est à dire une plus grande température critique.

Considérons maintenant de plus près l'interaction effective entre 2 électrons. Avoir une interaction de paire attractive est, au premier abord, surprenant. Des charges identiques se repoussent, de telle sorte que le potentiel de coulomb entre electrons soit ré-pulsif. Plus correctement, dans un métal, nous de-vrions prendre le potentiel de base comme étant un potentiel Coulombien répulsif avec écran, de préfé-rence à la forme libre e2 / r . La raison en est que dans un métal les électrons environnants forment un mi-lieu ou l'interaction prend place. Comme dans la théorie électromagnétique ordinaire, il faut alors divi-ser le potentiel par la constante diélectrique du mi-lieu. Ici, comme nous sommes plutôt intéressés aux interactions d'un point de vue microscopique nous aurons à faire à une fonction diélectrique plutôt qu'à une constante.

Dans la théorie de Thomas-Fermi le potentiel avec écran prend une forme de Yukawa en (e2/r)e~xr, ou À est l'inverse de la longueur d'écran. Ce potentiel est réduit en comparaison de e-/r , mais demeure répulsif. Même dans un traitement plus raffiné du phénomène d'écran, ou le potentiel par example peut devenir dynamique, le fait essentiel de l'écran est de réduire l'interaction, sans changer son signe. La source de l'attraction entre électrons doit se trouver ailleurs, dans l'existence du réseau d'ions ignoré jusqu' ici.

Comme point de départ je vais prendre un point de vue très naïf et classique. Bien que tout ne soit pas complètement exact dans ma description, j'espere cependant que le point essentiel ressortira clairement. Considérons un réseau d'ions. Nous pouvons nous limiter à 2 dimensions; chaque ion ayant une charge -|-Ze, comme le montre la fig. 1. La présence d'un électron en A, dans la fig. 1, aura pour effet d'attirer les ions vers lui, simplement car l'interaction élec-trostatique ion-électron est attractive. Un 2 ième élec-tron arrivant se trouvera effectivement attiré vers la région de densité ionique accrue par rapport a la moyenne; ainsi nous obtenons effectivement une at-traction entre deux électrons.

J'espere que cette description simple rend vrais-semblable la possibilité d'une interaction attractive electron-électron, produite par la polarisation du ré-seau crystallin. Ceci est très important pour la supra-conductivité. Si cette attraction est assez grande pour annuler et dépasser la répulsion coulombienne, alors la condensation se produira.

60 / Physics in Canada

Bien des choses sont fausses dans ce modèle sim-ple, et il ne doit pas être pris trop sérieusement. J'aimerais discuter brièvement de quelques unes de ses limitations pour montrer qu'il vaut mieux être pru-dent et que les choses ne sont pas si simples. En for-mulant mes arguments, j'ai pris les électrons comme localisés, bien que du point de vue de la mécanique quantique je les sache être dans des états représentés par des ondes planes, et il vaudrait mieux parler d'ondes polarisées. De plus, les électrons se propa-gent à la vitesse de Fermi, 10:i fois grande que la vitesse du son qui nous donne la vitesse de réaction du réseau à une variation de densité de charge. L'in-teraction propagée par le réseau doit présenter d'im-portants caractères retardés. Nous avons négligé ceci dans notre description, même si les conséquences peuvent être importantes.

O o o

o

o

o

a

A e -

Gf 'G

O

O

O

O O O Fig. 1 Chaque ion a une charge Ze. L'électron en A attire vers lui les ions de son environnement . Un second électron sera alors attiré vers A en raison de l 'accroisse-ment de la densité d ' ions dans cette région.

Je veux maintenant discuter, avec quelques détails, les facteurs principaux contrôlant la grandeur de l'in-teraction électron-électron propagée par le réseau. Dans un métal, chaque ion est condensé à sa position d'équilibre, et se trouve au fond d'un puits de poten-tiel profond provenant des autres ions et électrons. Lorsque les déplacements hors de la position d'équi-libre sont petits, on peut utiliser l'approximation harmonique, caractérisée par une constante de rap-

grande puissent

pel. Si cètte constante est importante, il sera relative-ment difficile d'obtenir une réponse significative à une fore; d'entraînement. Dans notre cas, cette force provient du potentiel entre un électron de conduction et l'ion. Il va sans dire que dans un réseau d'ions nous avons un système d'oscillateurs harmoniques couplés de telle sorte que les modes normaux de vi-brations du système soient collectifs. Je parlerai néanmoins d'un seul oscillateur harmonique forcé. Plus la force d'entraînement est grande, et plus la constance de rappel est faible, plus la polarisation du réseau elst alors importante et donc plus T(, est grand.

De ce point de vue nous aimerions un réseau mou, très défprmable, et une interaction électron-ion très

de telle sorte que les électrons de conduction réellement secouer le réseau. Bien sûr pour

un métdl déterminé, il va sans dire que ces deux pro-priétés ne peuvent pas être changées indépendamment à volonté. Cependant, ce sont ces 2 propriétés que je veux méttre en lumière.

Commençons par une discussion de la dynamique du réseiu. Nous pourrions essayer un calcul, suivant les pretpiers principles, des constantes de rappel des ions, où bien des modes normaux de vibrations du réseau. Ceci introduirait inévitablement des incerti-tudes. 11 n'est pas nécessaire de procéder ainsi puisque nous pouvons nous servir de la technique de diffusion inélastique de neutrons pour mesurer avec une bon-ne précision les vibrations atomiques. Les neutrons thermiques à notre disposition autour des réacteurs de haut flux sont, pour ceci, idéal. La raison en est que pour une longueur d'onde de neutron égale à la distance entre atomes, l'énergie correspondante du neutron est du même ordre de grandeur que l'énergie typique d'un phonon (c'est à dire quelques meV). Par phonon je veux dire simplement un mode nor-mal de vibration du réseau.

Les neutrons se trouvent couplés aux ions, en rai-son de leur champ nucléaire interagissant avec les noyaux de ces ions. Il n'y a pas de couplage direct entre les neutrons et les électrons de conduction. Donc, quand un neutron se propage a l'intérieur d'un crystal, il peut exciter le réseau directement dans un de ses modes de vibrations. Pour un transfert en mo-ment fixe, les neutrons diffusés peuvent être analysés du point de vue de l'énergie transférée. Lors de cette analyse on trouve un groupe de neutrons bien défini et centré autour d'une énergie identifiable a l'énergie du phonon ainsi excité. La largeur du groupe est, bien sûr, reliée a la durée de vie du phonon. De cette façon les courbes de dispersion des phonons peuvent être déterminées, c'est à dire la courbe de fréquence

ùj en fonction du vecteur d'onde k peut être tracée pour les modes normaux de vibrations.

En pratique, les mesures sont d'habitude limitées aux valeurs de k dans les directions de haute symé-trie du crystal. Bien que celles-ci forment un groupe bien limité par rapport au nombre total, leur con-naissance est souvent suffisante. Les phonons, dans une direction générale, peuvent être déduits des don-nées de haute symétrie. On procède en utilisant une analyse des constantes de force suivant la méthode de Born von Karman. Dans ce modèle, des constan-tes de rappel sont attribués entre chaque atome et ses premiers voisins, 2è m e voisins, 3ème ... etc. En principe, si ces constantes sont connues pour une distance arbitrairement grande entre atomes, la dyna-mique du réseau se trouve complètement déterminée. Pratiquement, on suppose que les forces entre ions ne sont pas à trop longue portée et qu'il est raisonnable de considérer les constantes de rappel au delà du

nème voisin comme suffisamment petites pour être négligées. Ainsi réduit-on le nombre de paramètres à une quantité finie; leurs valeurs sont déterminées par ajustement, au moyen de la méthode des moindres carrés, aux phonons mesurés dans les directions de haute symétrie2.

Ces constantes connues, il n'est pas difficile de dé-terminer les phonons pour n'importe quelle valeur de k. Le problème se réduit à la diagonnalisation d'une matrice 3 X 3 au point k, appelée matrice dynami-que. Les trois valeurs propres de cette matrice sont les fréquences de phonons, à k. et les vecteurs propres sont les vecteurs de polarisation'1. La dynamique du réseau est, ainsi, complètement déterminée. La préci-sion de cette méthode est seulement limitée par la qualité de l'ajustement aux valeurs expérimentales, donc à la précision de ces données expérimentales, et aussi par notre hypothèse de constantes de rappel nulles à longue distance. Dans le Plomb, il y a des évidences pour croire en des forces de longue portée et certains auteurs4 ont suggéré que l'ajustement ac-tuel avec 8 plus proches voisins seulement n'a pas encore convergé. Ceci peut conduire à des erreurs importantes dans le cas des phonons généraux cal-culés avec ce modèle. Dans la plupart des métaux, cependant, cette difficulté n'existe pas et peut donc être ignorée.

Pour terminer cette discussion, j'aimerai encore une fois vous rappeller que si y est une constante de rap-pel moyenne et M la masse de l'ion, une fréquence de phonon typique est co = V ' y /M . Donc pour un réseau mou, facilement polarisable, y sera petit et par conséquent w aussi. Toute autre chose fixée par

La Physique au Canada / 61

ailleurs, plus le nombre de phonons de basse fré-quence sera élevé, mieux ce sera pour la supra-conductivité.

La deuxième quantité importante à examiner est la grandeur de la force d'entraînement, c'est à dire la grandeur de l'interaction électron-ion. L'hypothèse la plus simple est de prendre cette force comme don-née par la charge Z de l'ion, puisque celle-ci déter-mine la force électrostatique électron-ion a longue portée. De ce point de vue, plus Z est grand, plus grande sera l'interaction électron-ion, ce qui est d'au-tant mieux pour la supraconductivité. Bien que ce schéma simple soit partiellement valable, il ignore cependant la structure interne des ions et exagère ainsi la grandeur de l'interaction électron-ion. En passant, mentionnons à ce sujet que les métaux monovalents, comme les alcalins et les métaux nobles, n'ont pas encore été observés dans un état supraconducteur. De tout les métaux élémentaires simples à deux électrons par atome, aucun n'est un supraconducteur de T,. > 1 °K, exception faite du Mercure, qui a cependant une température de Debye exceptionnellement basse indiquant un réseau très mou.

Un autre système à mentionner est la série d'al-liage T1 — Pb — Bi. Dans cette série il est possible de faire varier la charge effective par ion, Z*, sans chan-ger la structure du réseau. Pour les personnes moins habituées à la physique de l'état solide, je mentionne qu'en solution, le Tl a 3 électrons, le Pb 4 et le Bi 5. Expérimentalement5 il est connu que les phonons ne dépendent pas radicalement de Z*. La température critique varie cependant et cette variation dépend directement de la croissance de l'interaction électron-ion avec la croissance de Z*.

Au cours des années précédentes, des progrès ont été accomplis dans la connaissance de la grandeur de l'interaction électron-ion dans les métaux simples, par l'intermédiaire de la théorie du pseudo-potentiel électron-ion. Dans cette théorie on utilise un pseudo-potentiel effectif faible, plutôt que le champ de Hartree de l'ion, qui est fort. C'est une situation très favorable, car on peut alors partir de fonctions d'ondes planes pour les électrons de conductions et traiter la présence des ions comme une faible perturbation.

Je vais simplement donner une brève description des idées à la base du concept du pseudo-potentiel. Considérons un ion Na+. 11 a une configuration de gaz inerte et donc l'addition d'un électron supplé-mentaire pour former un atome ne déformera pres-que pas les orbites internes. Il est alors raisonnable de supposer que l'électron supplémentaire ressent le

62 / Physics in C a n a d a

champ de Hartree de l'ion isolé N a + . La fonction d'onde de cet électron est donc obtenue par solu-tion de l'équation de Schrodinger avec ce champ de Hartree. On ne doit pas oublier que cette fonction d'onde doit avoir un caractère 3s, car les orbites ls et 2s sont déjà occupées. En d'autre mots, on doit choisir une fonction ayant suffisamment de zéros pour la rendre orthogonale aux fonctions internes. Plusieurs zéros impliquent des oscillations importantes, d'où une énergie cinétique importante à l'intérieur de l'ion, qui doit annuler, au moins partiellement, l'at-traction du champ de Hartree. Cette annulation est à la base de la théorie du pseudo-potentiel, et peut être décrite de plusieurs façons. Je vais discuter cette an-nulation pour le cas spécifique d'un métal.

Dans un métal, nous savons que l'approximation des électrons libres est dans un sens valable. Ce modèle donne des fonctions d'ondes planes qui sont plutôt bonnes dans les régions comprises entre les ions, où le potentiel est faible. A l'intérieur d'un ion le potentiel est, au contraire, important, et, comme nous venons de le voir, la fonction doit avoir des oscillations rapides de façon à la rendre orthogonale aux fonctions d'ondes internes. Il paraît alors raison-nable de modifier l'ensemble des ondes planes en projetant, hors de cet ensemble, le sous ensemble des fonctions appartenant aux ions. L'orthogonalisa-tion est ainsi garantie. On appelle la fonction d'onde plane une pseudo-fonction d'onde, dont on obtient la vraie fonction par orthogonalisation. Il est alors possible de reformuler l'équation de Schrodinger or-dinaire pour les pseudo-fonctions d'ondes. La forme de cette équation nouvelle est la même que pour une vraie fonction d'onde, à condition de réinterpréter les parties d'orthogonalisation comme donnant lieu à un potentiel répulsif supplémentaire a l'intérieur de l'ion. Le champ de Hartree additionné à cette partie répulsive donne un faible pseudo-potentiel dont l'effet sur les électrons est traité par la théorie des pertur-bations.

Les pseudo-potentiels peuvent être déterminés par un calcul fondamental, qu'il est difficule de faire avec précision. D'autre part, on peut introduire des para-mètres dans le pseudo-potentiel, que l'on peut alors déterminer par des données expérimentales. Plusieurs modèles de pseudo-potentiel ont été introduits : Heine et Abarenkov® on suggéré une telle paramétrisation. Celle de Ashcroft7 est plus simple et contient un seul paramètre. Le pseudo-potentiel de cet auteur est obtenu simplement en assumant une annulation complète a l'intérieur d'une sphère de rayon R,., et une forme en Ze2 /r à l'extérieur. La valeur de R,. peut être déduite,

par exerfiple, des données de résistivité du métal liquide. Une vérification de consistence est que R,. doit avoir une valeur comparable au rayon de l'ion. Le pseudo-potentiel ainsi obtenu peut être utilisé dans le calcul de la supraconductivité.

Nous avons maintenant décrit toutes quantités né-cessaires pour effectuer avec succès le calcul de Tc. Pour procéder il nous faut cependant une théorie de la supraconductivité reliant les interactions à la gran-deur de T,.. Il existe une très belle et exacte formula-tion de la théorie dite de "pairing"; c'est celle de Eliashberg8. Elle utilise les fonctions de Green ther-modynamiques et représente un progrès par rapport à la théorie de B.C.s. Le travail de Eliashberg est encore pasé sur les idées de "pairing" développées par B.C.S., mais sa nouveauté consiste en un for-malismq suffisamment général pour tenir compte des détails des interactions. En particulier, la nature dy-namique de l'interaction entre électrons, ayant son origine dans la polarisation des ions, est facilement inclue, te qui n'est pas le cas dans le travail de B.C.S.

En effet B.C.S. introduisent un élément de matrice moyen pour décrire d'une façon approximative l'in-teraction effective entre 2 electrons au niveau de Fermi. Mais comme nous l'avons vu les interactions entre électrons sont très complexes, et il y a peu de chance de résumer complètement leur effet en un seul paramètre, qui oublie tout détail. Dans la théorie de Eliashberg, il n'est pas nécessaire d'effectuer quel-que approximation que ce soit au sujet des interac-tions.

Eliashberg utilise un système d'équations intégra-les nori linéaires et couplées, assez complexes. Leurs détails sont sans importance ici et il suffit de savoir que loitsque les noyaux de ces équations sont connus, elles peuvent alors être résolues numériquement et donner une valeur exacte de A ou T,.. Il est impor-tant de réaliser cependant qu'il y a des évidences pour croire que ces équations contiennent toutes les corre-lations importantes. Le problème de la supraconducti-vité est donc réduit au calcul des noyaux de ces équations.

noyaux peuvent être réduits" à une fonction F(a>) se référant à la partie de l'interaction

£ée par les phonons et à une constante, Uc, se rapportant aux répulsions coulombiennes. Permetlez-moi de donner quelques explications. La différence d'énergie entre les phases supraconductrice et nor-male èst très petite. Seul un petit nombre d'électrons au voisinage de la surface de Fermi sont affectés dans une bande d'énergie de quelques meV seule-ment, qui doit être comparée à l'énergie de Fermi ~

3 eV. Dans cette petite région, autour du niveau de Fermi, les répulsions coulombiennes entre élec-trons ne subissent aucune variation importante, car leur échelle est celle de l'énergie de Fermi. Une seule constante peut donc caractériser cette interaction. D'autre part les énergies des phonons sont de l'ordre de quelques meV et, donc, une fonction complète est nécessaire pour décrire leur effet, même à l'inté-rieur de la très petite bande d'intérêt.

Le problème est le calcul de ar(o>) F(w). Tout ce qu'il nous faut pour le résoudre a été exposé. En utilisant la théorie des perturbations dans le traite-ment de l'interaction électron-ion, on peut obtenir une formule donnant a-(w) F(w) avec une bonne exactitude. Cette formule contient le carré du pseu-do-potentiel, ainsi que les fréquences renormalisées et les vecteurs de polarisations des phonons; elle décrit la diffusion d'électrons à la surface de Fermi vers des états finaux arbitraires de cette même sur-face, par échange de phonons virtuels. La limitation de l'espace de phase à la surface de Fermi provient du fait que les énergies des phonons sont négligeables par comparaison à l'énergie de Fermi. Pour une sur-face de Fermi sphérique l'intégrale double de surface déterminant a2(w) F(&/) se réduit à une intégrale triple sur les transferts en moments q entre l'état ini-tial et final de l'électron, qui peut être effectuée nu-mériquement pour obtenir a-'(w) F(w) en fonction de

Je pourrais vous donner une forme explicite de a-(cû) F(ÛJ). Puisque j'ai déjà décrit les aspects im-portants de ce résultat, il n'est pas nécessaire de l'écrire. II est probablement plus fécond d'en voir le sens physique. Très approximativemment on peut interpréter a 2 (w) F(CO) en termes du diagramme don-né par la fig. 2. Considérons la diffusion de 2 élec-trons par échange de phonons virtuels. Comme le montre la fig. 2, a-(co) peut alors être interprété comme donnant la grandeur de couplage au vertex electron-phonon et F(w), densité d'état des phonons, contient les informations concernant les particules échangées.

Les premiers calculs effectués111 dans le cadre que nous venons d'indiquer, l'ont été pour Al et Pb, ainsi que pour Na et K. Nous avons trouvé que, pour Al et Pb, la valeur de T c prédite correspond à la valeur expé-rimentale à 15% près. La différence de valeurs de T,. entre ces 2 métaux correspond a un facteur de 5. La raison en est que le réseau du plomb est plus mou que celui de l'Ai, et que l'interaction électron-ion est plus grande dans le plomb, qui a 4 électrons par atome, que dans l'Ai qui en a 3. En effet, dans le

La Physique au C a n a d a / 6 3

Y y

Fig. 2 Interact ion entre deux électrons par échange de phonons , c 'est-à-dire produi te par l ' in termédiaire de la polarisat ion du reseau, r ( to ) est la densi té d 'é ta t des phonons et a (w) nous donne la g randeur du couplage au vertex é lec t ron-phonon.

plomb F(OJ) est complètement contenu dans l'intervalle w = 0, K) meV. Pour Al c'est plutôt a> = 0, 40 meV. De plus, en amplitude, a-(a>) F(CO) est plus petit dans Al que dans Pb.

De façon à vérifier que ce premier succès ne n'est pas fortuit, d'autres calculs ont été entrepris. La série d'alliages Tl-Pb-Bi a été étudiée en détail. Les courbes de dispersion de phonons sont connues. La distribution des phonons en énergie F(W) est aussi connue11 d'après une analyse des données expérimen-tales suivant la méthode de Born von Karman. D'une façon approximative on peut conclure que les pho-nons sont assez stables pour cette série. Il est vrai qu'il y a une redistribution des modes de vibrations; d'un alliage à l'autre, mais aucun changement systé-matique n'apparaît. Pour cette raison on trouve que les changements de T,.12 dans cette série sont dus essentiellement aux variations de l'interaction élec-tron-ion, introduites par la variation de la charge effective Z*. T,. croît avec Z* et la variation de T,. d'un facteur de 4 au long de cette série est comprise sans difficulté. Dans chaque cas les T,. prédits s'accor-dent aux valeurs expérimentales à 15% près.

A titre de contrôle, des expériences d'effet tunnel12

ont été effectuées dans ces alliages. Cet effet permet un contrôle détaillé de la variation, suivant la fré-quence, prédite pour a2(w) F(co). On peut dire que ceci donne une confirmation très convaincante de l'exactitude de nos résultats. Pour cette raison, j'ai-merais décrire un peu plus ces expériences d'effet tunnel. Des jonctions peuvent être fabriquées, con-sistant en un film supraconducteur, puis une couche d'oxyde et, enfin, un film de métal normal. Même si les électrons ne peuvent pas diffusés à travers cette barrière de potentiel, c'est à dire la couche d'oxyde,

64 / Physics in Canada

il leur est cependant possible de passer, par effet tun-nel, d'un bord a l'autre, à condition que la couche d'oxyde ne soit pas trop épaisse. D'ordinaire cette couche est de quelques À. Les caractéristiques, cou-rant ( I ) - voltage (V) , de cette jonction peuvent alors être étudiées. On trouve que, pour I en fonction de V, il y a une structure13 correspondant à la struc-ture de a2(w) F(w) pour le métal supraconducteur. Ceci ne doit pas surprendre puisque ce sont les phonons qui causent la supraconductivité. Pour certains métaux, comme les alliages Tl-Pb-Bi, cette structure est de résolution suffisante pour en déduire cr(a)) F(w) avec précision. L'effet tunnel nous donne donc une autre méthode pour obtenir des informations sur F(co), d'une façon plus directe que la diffusion des neutrons, et peut être aussi précise.

Dans l'alliage Pb4Tl(!, où il existe des données ex-périmentales précises pour les 2 méthodes, on trouve un accord important quant à la forme de cr(w) F(co) en fonction de co. L'effet tunnel donne cependant un spectre plus étalé qui celui calculé à partir des don-nées de diffusion des neutrons. Les positions des pics sont néanmoins en accord complet14. De plus les différences qui demeurent sont facilement comprises. Dans un alliage, les phonons ont une durée de vie finie, en raison des fluctuations d'ion a ion. Ceci donne directement un étalement des groupes de neu-trons. Une analyse des courbes de dispersion par la méthode Born von Karman ignore cependant ces étalements. Les distributions de phonons F(w) qui en résultent montrent des singularités de Van Hove très prononcées. Les étalements auraient pour effet de les réduire. Il est difficile cependant d'effectuer un calcul tenant compte de ces étalements. Il y a peu de doute15, cependant, que ces étalements soient la source de difference entre a 2 («) F(«), derivée de l'effet tunnel et de la diffusion des neutrons.

Nous avons aussi calculé l'effet de la pression hydrostatique sur TV6'17. Pour les métaux simples, expérimentalement, T,. décroît lorsque la pression croît. Nos calculs montrent que cet effet est dû prin-cipalement à la tendance des phonons à se déplacer vers des plus hautes fréquences sous l'effet de la pression hydrostatique, qui durcit le réseau. Il est vrai aussi que l'interaction électron-ion change sous l'effet de la pression, mais ces changements sont très petits par comparaison à ceux induits dans les fré-quences des phonons. Notre théorie prédit avec pré-cision les changements de T,. observés expérimen-talement, bien qu'ils soient très différents dans le cas de Al et de Pb. D'autre part, pour Pb, nos calculs

nous indiquent que T0 et A varient18 différamment en fonction de la pression. Cet effet est en accord avec l'expérience19.

Nous ^vons encore un autre succès à mentionner20. Nous avons calculé l'effet du spectre des phonons sur l'anisotropie de A. Nous avons trouvé qu'ils sont la source la plus importante d'anisotropie et les valeurs obtenues pour cette anisotropic sont en accord avec l'expérience. Ces résultats ne sont pas encore com-plets, mais je les présente néanmoins comme une: autre évidence de la possibilité d'effectuer des calculs précis et détaillés des propriétés des supraconduc-teurs.

J'ai tenté de vous exposer, en termes les plus sim-ples possibles, les éléments principaux de la théorie moderne de la supraconductivité. J'ai essayé de faire ressortir leurs significations et leurs relations avec T r . J'ai discuté le calcul des paramètres principaux à partir dés données expérimentales concernant les phonons obtenus par la diffusion inélastique des neutrons ainsi qu'à partir de la théorie du pseudo-potentiel. L'effet tunnel a pu aussi nous donner des informations sur ces paramètres. D'une façon géné-rale, ce qu'il ressort, c'est qu'une interaction électron -ion importante, ainsi qu'un réseau mou, sont essentiels pour obtenir des grandes valeurs de T,.. En pratique, cependant, il n'est pas facile d'exploiter ces 2 possibilités au maximum et en même temps. Je pourrais m'étendre abondamment sur ce sujet mais je dois maintenant terminer.

It is a pleasure to thank P. Grangé for invaluable aid in the preparation of this article. Without his ad-vice my task would have been even more difficult. Much of the work described was started with Bob Dynes and continued with Peter Trofimenkoff and Richard Leavens. I have gained much from my inter-actions with them. David Goodings read the manu-script and made some suggestions for which I am grateful.

J . P . C A R B O T T E

McMaster University

REFERENCES

1. J. Bardeen, L. N. Cooper and J. R. Schrieffer. Phys. Rev. 106, 162 (1957); 108, 1175 (1957).

2. B. N- Brockhouse, T. Arose, G. Caglioti, K. R. Rao and A. D. B. Woods. Phys. Rev. 128, 1099 (1962).

3. G. Gilat and L. J.. Raubenheimer. Phys. Rev. 144, 390 (1966).

4. R. C. Dynes, J. P. Carbotte and E. J. Woll. Solid State Corrimun. 6, 101 (1968).

5. S. C. Ng. Ph.D. Thesis McMaster University (1967) 6. V. Heine and T. Abarenkov. Phil. Mag. 9, 451 (1964). 7. N. W. Ashcroft. Phys. Letters 23, 48 (1966). 8. G. M. Eliashberg. Soviet Phys. JETP 11, 696 (1960).

9. D. J. Scalapino, J. R. Schrieffer and J. W. Wilkins. Phys. Rev. 148, 263 (1966).

10. J. P. Carbotte and R. C. Dynes. Phys. Letters 25A, 532 (1967) and Phys. Rev. 172, 476 (1968).

11. B. N. Brockhouse, E. D. Hallman and S. C. Ng. In Magnetic and Inelastic Scattering of Neutrons by Metals, edited by T. J. Rowland and P. A. Beck (Gordon and Breach Science Publishers Inc. New York 1968).

12. R. C. Dynes, J. P. Carbotte, D. W. Taylor and C. K. Campbell. Phys. Rev. 178, 173 (1969).

13. W. L. McMillan and J. M. Rowell, In Superconductivity, p. 561, edited by R. D. Parko (Marcel Dekker, New York 1969).

14. J. M. Rowell. W. L. McMillan and W. L. Feldmann. Phys. Rev. 178, 897 (1969).

15. R. C. Dynes and J. M. Rowell. Phys. Rev. 187, 823 (1969).

16. P. N. Trofimenkoff and J. P. Carbotte. Solid State Com-mun. 7, 661 (1969).

17. P. N. Trofimenkoff. Ph.D. Thesis McMaster University (1969) .

18. P. N. Trofimenkoff and J. P. Carbotte. Phys. Rev. (in press).

19. J. P. Franck and W. J. Keeler. Phys. Rev. Lett. 20, 379 (1968).

20. R. C. Leavens. Private communication.

Report on the Second Annual Meeting of the Corporate Members

The Second Annual Meeting of the Corporate Mem-bers of the CAP., was held at the Ritz Carlton Hotel in Montreal on January 30, 1970. This meeting brought together 85 representatives; from industry (37), and senior physicists from universities (36) , and from government (12), to exchange views on present day needs and problems of mutual concern. Chairmen from physics departments across Canada were present as well as the executive and council of the CAP. and discussions were both lively and useful. The meeting was supported in part by a contribution from the Office of Science and Technology of the Department of Industry. A noon reception was sponsored by Hydro-Quebec and Bell Canada entertained with a reception following the afternoon session. We believe that a meeting of this kind was unique not only to phy-sicists, but to scientific societies in general.

Following introductory remarks by A. G. Lester, Executive Vice-President, Bell Canada, who chaired the morning session and E. W. Vogt, Vice-President CAP., Dr. A. DesMarais, Principal Science Advisor, Science Secretariat outlined the formal organization of

La Physique au C a n a d a / 65

the various groups advising the Government of Cana-da on Science Policy. He pointed out that the Science Secretariat headed by Dr. R. J. Uffen is an organiza-tion within the government responsible for advising the Cabinet confidentially on matters relating to Science policy on a daily basis. The Science Council, chaired by Dr. Solandt, on the other hand is a group outside government who advises on medium- and long-term fundamental issues in Science. It is expectcd that a detailed account of this report can be given in a separate article.

Professor L. Katz, of the Science Council presented a view of Science Policy and Canadian Physics. He in-dicated that past policies (e.g. all scientists in the country meet for decisions) are not adequate for the present nor can they be extrapolated to present and future needs. Can we say today "Support the man not the project"?

The Science Council was founded by parliament fol-lowing recommendations of the Glassco Commission and it consists of 25 members and 4 associate mem-bers, all highly qualified people who serve for periods of one to three years.

Until now the Council has published three kinds of reports. The green cover contains reports prepared by committees appointed by council, the red cover contained the Science Council's official reommended policy and the annual report (blue), ft is expected that future reports will contain all of these in one with the various parts very clearly separated.

The Science Council has suggested that science policies will be relevant if they are tied to national goals, and they have indicated how science and tech-nology can help to achieve these goals.

Two programmes have been proposed following an earlier decision to "choose a few areas and establish major programmes in these areas". They are, space interest and water source management and develop-ment. At least two further suggestions are presently being considered by the Council.

Mr. L. Hynes, president of C.I .L. and a membor of the Science Council presented an Industrialist's View of the Science Council. He reviewed the national goals which are summarized as an improved quality of life for all Canadians, which contain elements in the area of: national prosperity, health, education, freedom (security, unity), leisure and world peace. He noted that these goals cannot be achieved without careful planning. As an example, Mr. Hynes suggested that one cannot simply provide more and better education without proper social and economic planning, other-wise we could have large numbers of trained people

6 6 / P h y s i c s in C a n a d a

underemployed. During his discussion of the evolution of National Science Policy from national goals by an operational type of analysis, he urged more interdisci-plinary training. In formulating Science policy, he in-dicated that a matrix of functions and goals could be used to indicate what is needed and hence what is missing. He emphasized that an industrialist must be a generalist knowing how to integrate specialists.

Dr. Ara Mooradian, Head, Whiteshell Laboratories, A.E.C.L . at Pinawa, Manitoba discussed the develop-ment and operation of a science based research estab-lishment in the present Canadian context. Whiteshell Nuclear Research Establishment (WNRE), is an isolated scientific community, a research and develop-ment centre, attempting to mature in today's environ-ment. It is attempting to demonstrate that research and development are rewarding and necessary activities worthy of public and private support, W N R E , after studying the world nuclear scene found that three con-siderations had dominated all of the significant pro-grammes, namely: capital cost, efficiency of operation and neutron efficiency. Canada's effort, through the insight of Dr. W. B. Lewis, was directed toward the latter and after experience with mature industrial plants, Canada's competitors in this area are now focusing their attention on the neutron economy and efficiency promised by the Sodium cooled fast reactor. In actual operation he noted that the laboratory profits by interdisciplinary intercourse and is presently find-ing that it can profit greatly by being multi-functional as well. The scientist is stimulated to direct even his fundamental programmes along lines which develop him as a valued consultant. The engineer is learning to impose fresh demands on the scientists and not to be slavishly confined to his handbooks. Scientists at W N R E are held responsible for their internal adminis-tration and financial control and are expected to de-velop their executive as well as technical potential. It was pointed out that W N R E was launched in 1959 and is expected to be a fully mature operation by 1974, some 15 years later. When one compares this with the challenge facing Canada, Dr. Mooradian suggested that if we grow too fast we could suffer in quality and waste money and if we grow too slowly we may lose our most precious assets by emigration or disillusion-ment.

The afternoon session dealing with the industrial research environment in Canada was chaired by R. T. E. Gillespie, General Manager, Electronics Compo-nents Division of Canadian General Electric. Four views were presented, then the four speakers as a panel, took part in a general discussion.

F. J. McMulkin, Vice President, Research, DOFASCO

presented the case for a research environment in heavy industry and the picture presented did not flatter pres-ent university programmes. He emphasized that al-though present PH.D. programmes are aimed at basic research, industry requires experience in applied re-search. The four processes of R and D include discov-ery, invention, innovation and imitation and experience in the Stelel industry suggests, the last two are the most important. An immediate research problem is solved by taking it to a commercial research institute or to the appropriate specialist and his instrument. Gene-rally short range work is required, because it is part of a bigger programme being carried out at the plant. This tends to eliminate the use of University or governmènt laboratories because of their long term thinking. Competition seems to be best met by rapid adoption! of available technology and the basic re-search that led up to this is generally well publicized long befdre it is adapted, especially in the steel indus-try. It was stated that the Japanese steel growth, on the technical side has probably been due to their adoption of available technology rather than due to basic dis-covery. Government incentive programmes are not generally effective in heavy industry, since the only cri-terion fqr doing research is: is there an economic in-centive in terms of improving the company's profit position? However, the incentive plans are useful and desirable for small industry trying to obtain bigger markets In his discussion of research manpower Mr. McMulkin stated that the industrial requirement was for a practical type of graduate, and the quality of manpower coming from the universities is a particu-larly frustrating problem. It seems that 95% of the research monies given to the universities is apparently aimed at producing basic research PH.D. 'S which tax-paying Canadian industry cannot use and does not want. How do we turn off the flow?

Another point of view was expressed by D. Chib-holm, Vice President of Northern Electric. He said that ne\|v PH.D. graduates are our most important na-tional resource, but the problem is utilizing them. Few Canadian industries can use them directly. In small companies the new PH.D. finds himself in a strange new environment like a boy scout in his first craps game. He is a hardware specialist, who has avoided dealing with people. In choosing a new PH.D., the research director finds that two things correlate. If he worked with a great man, he is better; if he finished his degree one ye^r sooner than the average, he is more ambi-tious and hence the PH.D. can be used as a sieve to select people with more motivation. When a physicist joins a small company he is never a physicist again, until the company grows bigger. This is a problem for

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the new graduates who have traditionally expected to continue the work contained in their thesis. Another serious problem was expressed by Dr. Chisholm in the form of a question. How do you get specialists in two different fields to communicate with one another?

The Vice-Recteur Université Laval, L. P. Bonneau discussed the supply and demand for PH.D. 'S in Cana-da. An analysis of supply and demand for scientific man power in Canada obtained from a survey taken in August 1968 was presented and it clearly indicated that the supply of PH.D. 'S in pure and applied scien-ces would exceed the demand in 1970 or 1971. After a negative first reaction to these facts, it was felt that the issue was not whether we should surrender the effort to train our best brains but rather how the de-mand can be stepped up. The demand curves indicated that Universities will employ the largest percentage of PH.D. 'S (about 7 0 % ) by 1975, while government will employ 17% and industry only 13%. The problem is clearly the lack of industrial demand and this poses a few questions. How is it that industry has been unable to improve this pattern? By what means can this pic-ture be corrected to ensure a higher demand growth rate for PH.D. 'S in industry? Some factors contributing to the present problems were presented. Witnesses, before the Lamontagne Committee told of subsidiaries of foreign-owned companies importing their techno-logy into Canada and the need to correct this. The re-cent o.E.c.D. report indicated that foreign control over many major firms within Canada leads to initiative and decisions being taken outside Canada. Research staffs often merely lend a prestige clement to the Sales effort and wards off criticism that the parent plant is preventing research development in the Canadian branch plant. This view is popularly held across Cana-da and should not be taken lightly, since this issue stands at the very crux of Canada's concern about the Canadian economy and research and development in Canada. Dr. Bonneau suggested that the federal gov-ernment should place the branch plants on the same footing as an autonomous plant and encourage them to undertake research through liberal fiscal policies. The government could set aside larger sums for indus-trial research to help industry increase its demand for PH.D. 'S . This is important since generally speaking, the rate of growth in the number of PH.D. 'S in pure and applied science is closely related to a country's eco-nomic growth. The PH.D. in pure or applied science is the base unit in the human resource, exercising the most influence on an industrialized country's economy and technology.

S. Wagner, Director General, Office of Science and Technology, Department of Industry Trade and Com-

L a P h y s i q u e a u C a n a d a / 6 7

merce commented on the Federal R & D Incentive Programmes. Although some successes have been re-corded in these programmes, there is some disappoint-ment with the response of industry to increase the growth rate of R & D generally.

David Atherton, Head of Superconductivity Re-search at Ferranti-Packard Ltd. suggested that the dis-appointing growth of Canadian industrial research is due primarily to the poor profitability of our research based industries. As an example of this he quoted the electrical industry and further suggested that if Gov-ernment policy could increase profits or reduce taxa-tion, there would be less need of further research incentives. Present Government incentive programmes allow no profit in Canada, and this constitutes a rea-son for not participating. To encourage industrial re-search in Canada we must encourage profits since every industry exists to make a profit and no company can survive indefinitely without it.

L. Berlinquet, Vice-président à de recherche, Université du Quebec, discussed L'Institut National de la recherche scientifique (INRS) and emphasized the close relationship between this government labora-tory located at Sainte-Foy, and the University of Que-bec. Some students will get graduate degrees while actually doing the research at the institute. The Uni-versity and the Institute will work on practical prob-lems of interest to Quebec. The Institute will play a determining role of a public nature and will call for collaboration, and cooperation with all of the Univer-sities private or public in Quebec.

Lionel Boulet, Directeur, L'Institut de recherche de l'Hydro - Quebec, urged the university teachers to take a critical look at themselves and he suggested that the scientific world has lost contact with the people. Our public relations have been neglected. How can we convince people that technical research promotes the well being of everyone? Scientists have provided tech-nical advantages and ignored the social problems these introduce. Scientists defended their specialty and con-sidered for example that social sciences were worth-less. Scientists have been interested in sophisticated gadgets and now the electrical industry, expanding very rapidly at the present time, cannot find the hard-ware and manpower they need. The Institute has been set up to do basic, and applied research as well as de-velopment and as any good laboratory, employs teams of scientists and engineers working together. A pro-gramme of collaboration, involving the Institute and universities but under the supervision of one univer-sity, is being organized to provide a graduate course in energy designed to meet the demands of the people of Canada. He suggested that it is time the universities

68 / Physics in Canada

rejected the idea that they are the only possible degree granting centres in Canada, and they should seek to find the right men to educate young Canadians in such a way that they will contribute to the development of our country, whether that "right" man be in industry or a government laboratory. Universities at the present time cannot solve industries' problems, even though they have the money and the equipment because the professors do not know the problems. Dr. Boulet sug-gested there should be liberal exchange of personnel between universities and industries.

D. D. Betts, President CAP concluded the afternoon talks with a discussion of CAP programmes. These programmes were grouped under four headings, all member services, encouragement of excellence, plan-ning for the future and physics manpower. The first category includes those things which the CAP does for individual members, and represents direct benefits. These include "Physics in Canada ' containing a wide variety of articles of interest to physicists, and he re-minded members of industry and department chair-men that this is a useful medium in which to advertise. The Annual Meeting includes invited papers as well as contributed papers on a wide variety of interests in physics. Summer Schools are sponsored by the CAP, and some have become an annual event. There are presently seven divisions in the CAP with the prospects of two or three more being formed in the near future. It is possible for CAP members to subscribe to a variety of Journals (7), at reduced rates and it is expected the present list will be expanded considerably in the near future. Charter Flights organized by the CAP will be available to members from time to time. Various divi-sions of the CAP hold Topical Meetings on a regular basis. To encourage excellence, the CAP sponsors High School Prizes in each province as well as University Prize Examinations for graduating honours physics students. Both prizes are highly regarded. The CAP medal is awarded every year to a Senior Canadian Physicist who has made outstanding contributions to physics. The CAP Lectureship programme brings lec-tures of high reputation to deliver a CAP lecture to undergraduate physics students in each Canadian Uni-versity. These lectures are very well received and have done a great deal to promote the understanding of the frontiers of physics to undergraduates. In planning for the future, the CAP has become involved in projects concerned with the future development of physics in Canada. These include feasibility studies on a Particle Physics Programme for Canada, and a Plasma Physics Programme. Other divisions are preparing studies in various areas but they have not yet been submitted.

Canadian Association of Physicists was largely instru-mental in the establishment of SCITEC (See the March 1st, 1970 issue of this bulletin). The CAP is sponsor-ing a study in depth of the teaching of physics and the evolution of enrollment trends under the direction of L. R. McNarry of the NRC. This study will attempt to analyse the extent and implications of apparent wide-spread disenchantment with the physical sciences. Dr. Betts nçted that the CAP must involve itself in the growing problems of information dissemination and it plans to take an active interest in this area. Physics Manpower is the fourth major concern of the CAP and we have cooperated with that government department to provide a survey of highly qualified manpower in Canada A placement service for CAP members has been initiated, but only in a limited way due to finan-cial stringencies. A directory of employers of physi-cists in Canada is available to members on request. At the Annual Meeting lists of employers seeking physi-cists and physicists seeking employment are available.

Dr. Betts concluded his remarks with a comment on the fact that Canada is making very ineffective use of the trained manpower at present available to her arid he cited a specific example of one top graduate who has just completed a post-doctoral year with the lead-ing man in his field and he is unable to find any em-ployment in Canada. There is something gravely amiss in the Canadian utilization of some of its highly educated physicists.

D. E. BRODIE

Research in Physics at the University of Saskatchewan, Saskatoon

Physic^ research at Saskatoon stretches from the lofty heights! of the top of the atmosphere, where balloons and ropkets probe the environment, to the infernal depths of the linear accelerator, whose denizens study the atomic nucleus. Between these extremes is the plasma physics group who keep close to the surface of the earth and the theoretical group who on this scheme of things lie in limbo.

Upper atmospheric research in the department started as long ago as 1932 when B. W. Currie of I he Physic^ staff was given a two year leave of absence to participate in the Canadian programme for the Second

Fig. 1 Final adjus tments to the payload of a research rocket.

International Polar Year (1932-33). In the years following the polar expedition, B. W. Currie and his graduate students managed to maintain an upper at-mospheric programme by analysing results obtained during the expeditions. The improved finances of the postwar years brought staff additions, grants, con-tracts and the loan of equipment from government laboratories. These led to the development of spe-cialized instrumentation and techniques permitting in-vestigations not possible before. In 1957 an "Institute of Atmospheric Physics", attached to the Physics Department was established. In 1965 its name was

La Physique au Canada / 69

changed to "Institute of Space and Atmospheric Studies" in response to the worldwide interest in space research triggered by the first Sputnik. The division of Space Engineering was also established at that time.

The facilities of the Institute include a radio site 27 miles west of Saskatoon where J. B. Gregory and A. Manson use radio wave reflections at 2.2 MHz to investigate atmospheric waves and general dynamical processes in the lower ionosphere. G. Sofko using a polarimeter at 42 MHz studies the characteristics of the ionosphere and radar aurora. The morphology of radar aurora and its relationship to particle precipita-tion are studied theoretically by G. Sofko and A. Kavadas. Magnetic variations and micropulsations are investigated by K. Paulson who uses an array of digital magnetometers and specially developed signal pro-cessing techniques.

The active optical group (Llewellyn, McEwan, Montalbetti and Rundle), which is housed in the physics building has kept the Institute in the forefront of optical research with the study of aurora emissions and their relationship to the source of precipitating electrons, both from the ground and from balloons and rockets. Spectroscopic measurements of upper atmospheric temperatures, dayglow and twilight ob-servations and theoretical investigations of the atmo-spheric photochemistry are actively pursued. The work of this group is greatly assisted by an optics shop capable of building all but the most sophisticated optical systems. D. McEwan who joined the depart-ment last summer is continuing his research on the relationship between the flux and energy distribution of precipitating electrons and aurora using specially developed rocket-borne low energy spectrometers.

The Space Engineering Division, which is housed in a separate building away from the main campus, is supported entirely by contracts and is engaged in the design, construction and check-out of rocket pay-loads. In addition, the division may, under contract with any experimenter, undertake the design or con-struction of any experiment. Thus students from other departments or colleges often use the facility for their post graduate research and this gives it an interdisci-plinary atmosphere.

The Division also has a small research group (J. A. Koehler and A. Kavadas) who, with some collabora-tion with other Universities, study the auroral electro-jet, currents along the magnetic lines and electric fields using specially designed rocket-released probes.

Eleven years ago plasma physics research at the University of Saskatchewan in Saskatoon began in a corner of the basement in the old physics building with

70 / Physics in Canada

Fig. 2 Field-free plasma apparatus .

the construction of a high-field air-cored betatron for the investigation of runaway electrons (fast-streaming electrons) in a plasma. This work was initiated by H. M. Skarsgard and two graduate students - J. V. Gore and L. T. Shepherd. Large currents (up to 2000 Amps) of energetic (up to several keV) electrons have been generated in this and later versions of the experiment. During their brief lifetime the streaming electrons undergo a transformation of their directed energy into intense plasma oscillations, microwave-and X-radiation, and plasma thermal energy, thus obligingly providing a wide range of interesting thesis topics for graduate students. In order to obtain a better understanding of the processes responsible for the rapid slowing down of the streaming electrons, laboratory experiments are now supplemented by

computer simulation experiments aimed at following the evolution in time of the one-dimensional electron distribution function as well as various electrostatic plasma bscillation modes. The plasma betatron appa-ratus is also used to investigate non-linear processes in highly turbulent plasmas, i.e. plasmas characterized by large-amplitude oscillations. Under certain condi-tions rapid heating of the plasma ions is observed.

Nearly four years ago Drs. L. Schott from the Insti-tute for Plasma Physics, Julich, and G. Pocobelli, from the University of Rome, joined the plasma phy-sics group. Dr. L. Schott is investigating Langmuir probes in field-free plasma devices specially con-structed for this purpose. One of these, an 80-cm dia-meter spherical device, whose exterior consists of a shiny stainless steel shell with various ports and ob-

serving windows has prompted visitors to ask when it is planned to send her aloft! Actually "she" is used on the ground in order to investigate current collection by probes in weakly ionized plasmas for conditions rang-ing from collisionless to collision-dominated, as well as the disturbance of the plasma caused by the inser-tion of a probe.

Dr. Pocobelli's research is on the theory of plasma oscillations. He has developed a new technique for integrating the Vlasov-Poisson system when a mono-chromatic electrostatic wave is present in the plasma. The technique is now being employed in an investiga-tion of non-linear plasma phenomena. First results in this direction include the amplitude dependence of the dispersion of an electron plasma wave and the time behaviour of the damping coefficient of an ion wave.

Two years ago plasma physics research was moved to its new home in the modern Physics Addition, where it occupies seven separate areas one of which is an electronics laboratory. Besides the major experi-mental projects already described, there are ex-periments on radiation enhancement at the electron plasma frequency (Skarsgard), metastable atom inter-actions in plasmas (Schott), plasma confinement by a rotating magnetic field (Skarsgard) as well as smaller projects connected with the development of various diagnostic techniques.

In the 1950's the University of Saskatchewan gained world renown as a centre for photonuclear physics. In the past decade the old betatron was super-ceded by the present 140 MeV electron linear accele-rator, which under the direction of Dr. L. Katz has sustained the prestige of the university in the field of nuclear physics. It is hoped that the current decade will see the addition of a storage ring to the linac so that we may remain in the forefront of research in this field.

The work at the linac can be summarized as the study of the atomic nucleus through the electromag-netic interaction. This is a good technique as the electromagnetic interaction is well understood and sufficiently weak to be treated by established theoreti-cal methods. The general heading can be subdivided into three sections. First, the study of photonuclear reaction (Dr. W. Buss); second, the study of electro-disintegration (Dr. Y. M. Shin) and finally the study of electron scattering (Dr. H. S. Caplan).

The photonuclear work is, for the most part, the study of the energy spectra and angular distributions of neutrons emitted by nuclei under photon bombard-ment. The technique adopted is to irradiate the target

La Physique au Canada / 71

under study with a short ( < 10 ns) burst of X-rays and then to determine the energy of the neutrons by measuring the time they take to travel to detectors placed at a fixed distance from the target. At present, we can measure the yield at five angles simultaneously using five large scintillation counters as detectors and an XDS 920 computer to keep track of the events. The purpose of these experiments is to look for shell effects and correlations between nucléons in light nuclei.

In the electrodisintegration experiments the target is irradiated with a well-defined election beam and the charged particles emitted are analysed and identified by a 180 double focusing magnetic spectrometer with an array of semiconductor detectors on its focal plane. This system has been used to make an intensive study of the energy spectra and angular distributions of charged particles emitted from very light nuclei where there is some hope of performing realistic cal-culations.

Finally, in the electron scattering experiments, a magnetic spectrometer and scintillation counters are used to detect electrons scattered elastically or inelas-tically from target nuclei. The elastic scattering gives information on the size of nuclei and recent results are helping to show that the constant density model of nuclei merely indicates the trend of nuclear radii but is not correct in detail. The inelastic scattering has yielded extended information on electromagnetic tran-sition probabilities which provide an excellent means for testing proposed nuclear models.

Most of the theoretical work at Saskatoon is in low energy nuclear structure. To a large extent the prob-lems are associated with one or more of the linac experiments. E. Tomusiak is investigating the a-cluster model of some 4N nuclei to see whether or not cluster wavefunctions give characteristic features in their form factors. T. Brady and E. Tomusiak are in-volved in a theoretical study of the reactions He ' (y ,p)T and He4(y,n)He : !. The interest in this work arose from an experiment by Dr. Shin in which he found that there are pronounced differences be-tween the angular distributions of protons and neu-trons.

E. Tomusiak and R. Skinner are studying group theory together for application to nuclear and particle physics. R. Skinner is continuing his work on collective coordinates with V. Gupta (now at the University of Alberta) and also plans to continue his series of physics texts.

H E N R Y S. CAPI.AN

University of Saskatchewan, Saskatoon

Pictorial Facteria News/Nouvelles

A short course intended to familiarize science students with L I T E R O S C I E N T I C A M I C R O C O S O M M E S known to in-fect scientists.

Beast number 1 : Analogie Specificum: (known colloquially as an ana-logie)

Freshly cauglil analogie

Verbal attrit ion of a pet analogie can cause degenera-tion into a spheroidal verbal blur which has all attri-butes of a cliché.

Degenerate pet analogie

An analogie specificum is a multifaceted polyhedra of verbal origin. Has the useful ability to mirror in concrete terms abstract reality.

Can be housetrained and many people are known to have pet analogies. It should however be realized that most analogies have vicious stings in their tails and too frequent recourse to a specific analogie can result in paralysis of thought from a failure to realize this dan-ger. Pet analogies tend to degenerate in captivity and can become indistinguishable from a cliché.

HOWARD O'BRIAN

Ornery Lecturer in Nomotony Physics Dept. Alias: B. KAYE

Laurentian University

S U M M E R S C H O O L O N " D I F F R A C T I V E

P R O C E S S E S "

The McGill Summer School on "Diffractive Pro-cesses" from July 9 to July 17, 1969 was held on the campus pf McGill University in Montreal under the directorship of Prof. B. Margolis. The main subject of the Summer School was the higher energy diffractive scattering of hadrons on nucléons and nuclei. The subject discussed was of interest to both elementary particle physicists and nuclear physicists. The majority of the 200 or so participants were Canadian. Included among these Canadians were the participants of the Experimental Design Program who attended lectures in the morning and designed experiments at 200 geV in the afternoon. There were many visitors from most parts of Europe and the U.S.A. The nineteen speakers (listed at end of the article) represented different schools of thought in both North America and Europe. This wai a very important factor in making the Sum-mer School the great success that it was. The partici-pants wëre able to compare divergent points of view through the discussion that ensued between the pro-ponents of various viewpoints.

The emphasis of the Summer School was not on for-mal lectures, but on the exchange of ideas and the dis-cussion of difficulties in current research. This was ensured by scheduling the three formal lectures that were delivered each day during the morning hours. The afternoon hours were used for informal seminars which were invariably organized each day to discuss points raised during the formal lectures.

The main topic of the Summer School was diffrac-tive processes. We learned that resonance production reactions, in which the quantum numbers of the va-cuum may be exchanged, are very successfully under-stood iri terms of Pomeranchuk exchange. One of the very interesting points to come out of the Summer School was the idea that experiments with high energy beam and nuclear targets could be used to investigate in a very imaginative way problems in both nuclear physics and elementary particle physics. A typical example is that one could use production of A t in nuclei to determine whether the Ai is a kinematic en-hancement or an elementary particle. Since the nu-cleus acts as a filter the A, has a much better chance of not being absorbed if it is a particle rather than a 7r-p kinematic enhancement. There are many other examples of this type and it became evident that there

exists a large new field of investigation which has hardly been touched, i.e. the field of high energy nu-clear physics. Another topic which commanded the attention of the participants was duality. No definite conclusions were reached, but the adherents of oppo-sing viewpoints were able to learn from each other, a process which does not occur through the exchange of preprints but only through the personal confrontation that a summer school such as the McGill Summer School provided.

The list of speakers was as follows: C. Bemporad (CERN), L. Bertocchi (Trieste), A. Dar (Technion), S. Frautschi (Calif. Inst, of Tech.), R. Glauber (Har-vard), O. Kofoed-Hansen ( C E R N ) , M. Jacob ( C E R N ) ,

J. P. Lebrun (McGill), R. K. Logan (Toronto), B. Margolis (McGill), D. R. O. Morrison (CERN), A. Pagnamenta (Rutgers), M. Ross (Michigan), N. W. Tanner (Oxford), S.C.C. Ting (M.I.T.), J. Trefil (Illinois), W. D. Walker (Wisconsin), C. Wilkin (U. of London), J. Yellin (Berkeley).

In conclusion I would like to express the viewpoint that was shared by my colleagues by saying that the McGill Summer School was a great success and a very enriching experience.

ROBERT K. LOGAN

C A N A D I A N M E T E O R O L O G I C A L S O C I E T Y

The Canadian Meteorological Society will hold its fourth annual congress at Winnipeg on June 17-19, 1970. The meetings will be part of the general Learned Societies Conference, and will take place on the Uni-versity of Manitoba campus. The theme for one day of the meeting will be Education in Meteorology. This part of the program will encompass professional, tech-nical and school aspects of meteorological education and will include a panel discussion in addition to in-vited speakers. The remaining two days will be allo-cated to the presentation of contributed scientific papers.

M C M A S T E R T A N D E M A C C E L E R A T O R

At McMaster University, the tandem accelerator was formally accepted from High Voltage Engineering in February, 1969. At the present time eleven faculty members (Guelph, McMaster and Toronto) are using the facilities of the laboratory. About forty people, including 9 postdoctoral fellows, are using the machine regularly. It has been running at terminal voltages varying from 1.3 to 8.3 megavolts and delivering cur-

L a P h y s i q u e a u C a n a d a / 7 3

rents of various ions to the target as follows: protons and deuterons (up to 2 tjA), 'He (up to 0.4 ^A) Carbon (up to 3 /j,A) and Oxygen ions (up to 1 //.A). One experiment has also been carried out with a :iHe beam. A gas recovery system which will permit beams of :iHe to be used on a routine basis is nearing com-pletion.

PHYSICS AND CHEMISTRY OF SOLIDS U N D E R H I G H P R E S S U R E

An Advanced Study Institute on "Physics and Che-mistry of Solids Under High Pressure" will be held under the sponsorship of NATO at Delft, the Nether-lands, between August 2 and 14, 1970. Topics to be covered include high pressure studies on band struc-ture of semiconductors, electron transfer processes, magnetic properties, phonons, equation of state, phase transitions, sound propagation, metals, dielectrics, superconductors and various high pressure techniques. Further information may be obtained from the direc-tor of the Institute, Professor S. S. Mitra, department of Electrical Engineering, University of Rhode Island, Kingston, Rhode Island 02881.

E D U C A T I O N A L T R U S T F U N D

We are happy to mention that one of our members, who prefers to remain anonymous, has recently made a donation of four hundred ($400.00) dollars to the CAP Educational Trust Fund.

HAVE YOU CHANGED YOUR ADDRESS?

If so, please advise

Canadian Association of Physicists

Suite 903, 151 Slater St.

Ottawa 4, Ontario

Canadian Physicists Physiciens canadiens

AT MEMORIAL UNIVERSITY OF NEWFOUNDLAND ... DRS. C. W. CHO and N. D. FOLTZ attended the Conference on Non-Linear Optics at Queen's University of Belfast, and reported on their research using the gigawatt-pulsed laser ... DR. E. R. DEUTSCH collected rock samples for palaeomagnetic study in Ireland and Britain this sum-mer, and subsequently presented a paper at the meeting of the International Association of Geomagnetism and Aeronomy in Madrid ... DR. T. T. GIEN spent two months at the Centre for Nuclear Studies at Saclay and together with DR. J . D. MCANDREW, attended the McGill Univer-sity Summer School on Diffractive Processes in High-Energy Physics. Dr. McAndrew also participated in McGill's Experiment Design Programme ... DR. M. IRFAN was an invited participant in the International Confe-rence on Nuclear States held at the Université de Mon-tréal ... DR. s. P. REDDY and DR. VARGHESE presented a joint paper at the Symposium on Molecular Structure and Spectroscopy held at Ohio State University in Sep-tember ... During the summer DR. M. G. ROCHESTER gave invited papers at: the NATO Advanced Study Institute on Earthquake Displacement Fields and the Rotation of the Earth, held in London, Ontario, the NASA/MIT Summer Study on the Application of Space Science to Solid Earth and Ocean Geophysics at Williamstown, Massachusetts; and the Symposium on Electromagnetic Problems in Planetary Nanties at the University of New-castle-upon-Tyne. He also presented a paper at the Sym-posium on Geophysical Studies of the Evolution of the Earth's Deep Interior held in Madrid ... (This material was inadvertently omitted from the release that appeared in the November issue).

AT QUEEN'S UNIVERSITY ... DR. DONALD R. TAYLOR (Engi-neering Physics, Queen's 1962, M.A. Toronto 1963, PH.D. Oxford 1967) has joined the solid state group of Queen's Department of Physics to assume the position of Assistant Professor. He will set up a high resolution pulsed microwave spectrometer. From 1967 until Jan-uary 1970, he was associated with the Pure Physics Division of Bell Telephone Laboratories at Murray Hill, N.J., where he conducted a study of maser emission of high frequency sound waves.

AT THE UNIVERSITY OF TORONTO ... PRINCIPAL J . T. WILSON has been awarded the Medal of Service of the Order of Canada ... Four new postdoctoral fellows have recently joined the theoretical molecular and solid state physics group: DR. JOHN FLETCHER, from Nottingham University, has made contributions to the theory of Jahn-Teller effects and acoustic paramagnetic resonance ... DR. EUGENE TONG'S doctoral research was performed at the University of Alberta on Brillouin and Rayleigh scattering in liquids ... DR. JAN VLIEGER, whose perma-nent address is the Lorentz Institute, Leiden University, is perhaps best known for his work on the classical

statistical mechanics of electromagnetic phenomena... DR. KANG-PEI WANG, whose dissertation concerned the elec-tronic structure of alloys, will be working with both the experimental and theoretical solid state physics groups..

AT MCM/LSTER UNIVERSITY ... Recent PH.D.'S (Fall 1969) are: H. IYCKLAMA, now at Bell Labs, New Jersey; A. P. MILLER, now teaching at Brandon University, Brandon, Manitoba; J . F. A. MASON, who has joined the Univer-sity of Windsor; E. D. HALLMAN, now at the Laurentian University; j . R. COOK, now at Armco Steel Corporation Research at Middleton, Ohio; R. j . ATKINSON, now at the Univlersity of Buffalo, and M. A. BUCHANAN, who has gone to Oxford University on a NRC post-doctoral fellowship.

CAP Affairs Affaires de l 'ACP M E E T I N G O F E X E C U T I V E A N D C O U N C I L

R E U N I O N D E L ' E X E C U T I F E T D U

CONSEIL

Placement Service: The 1970 Directory of Employers of Physicists, prepared by the Committee on the Placement Service chaired by D. D. Betts, is now available free of charge to CAP members and at $2.00 per copy to non-members.

Canadian Journal of Physics: Proposals will be pre-pared by the CAP Committee on Publications arid submitted to NRC for the transfer of editorial responsi-bility for the Canadian Journal of Physics from NRC to CAP. Preliminary discussions have already been held between NRC (Dr. C. T. Bishop, Editor-in-chief of the Canadian Journals of Research, and Mr. H. William-son, Manager of the Editorial Department of NRC) and CAP (D. D. Betts, E. W. Vogt and J. L. Meunier).

Committee on the 25th Anniversary of CAP: The committee, chaired by L. Kerwin, submitted many recommendations; the following were adopted: (1 ) a past presidents' dinner to be held during the annual congress; (2) part of the special congress issue will be devoted to the 25th anniversary; (3) a new CAP medal - the Herzberg Medal - will be established to recog-nize outstanding achievement in any field of research by a physicist who, in the year of the award, is not more than 25 years of age; (4) delegates from the American Physical Society and the Sociedad Mexi-cana de Fisica will be invited to attend the banquet; (5) une demande a été faite à Radio-Canada pour la production d'un télé-film sur la physique au Canada;

(6) l'organisation d'une conférence sur l'évolution de la physique au cours des 25 dernières années et d'une autre conférence sur l'évolution possible au cours des 25 prochaines années.

Feasibility Studies: A proposal for a feasibility study on a national programme in plasma physics and tech-nology in Canada was submitted to NRC last January by the Division of Plasma Physics of CAP. Other pro-posals for feasibility studies are expected to be sub-mitted by other Divisions of CAP in the near future.

Lower Fees: Physics teachers joining as affiliate mem-bers will pay the reduced fee of $7.00 per annum for the first year of their membership in CAP, even if they are 30 years of age or older. Graduate students joining as full members will pay the reduced fee of $9.00 per annum, as long as they remain full time graduate stu-dents, even if they are 30 years of age or older.

Division of Atomic and Molecular Physics: The for-mation of this new Division was approved. A. I. Cars-well of York University was appointed pro-tem chair-man of the Division.

White Paper on Taxation: CAP will submit a brief to the Standing Committee of the House of Commons on Finance, Trade and Economic Affairs.

Congratulations to David Spurgeon: Official congra-tulations from CAP were sent to David Spurgeon, Science Writer for the Toronto Globe and Mail and Editor of Science Forum, on the occasion of the award of an honorary degree by Guelph University.

CAP Sponsorship: CAP has accepted to sponsor the three-day seminar on Nuclear Theory to be held at Queen's University at the end of August 1970.

T H E C A P S O C I O - S C I E N T I F I C

R E S E A R C H P R O J E C T O N S T U D E N T

A T T I T U D E S T O W A R D S S C I E N C E

This project has received the endorsation of all of the Provincial Departments of Education and most of the major educational organizations in Canada, as well as individual sociologists, physical scientists, educators, and many others. Yet as M. P. Bachynski has pointed out in the February issue of Science Forum, socio-scientific research is the orphan among the funding agencies.

By now the CAP basket, that has been sheltering this orphan, is becoming rather weather-beaten after sitting on the steps of the various funding agencies for the past eight or nine months.

La Physique au Canada / 75

Conceived in the spring of 1969 as a "Study in the Teaching of Physics and the Evolution of Enrolment Trends in Physics"*, the study has evolved through funding experience and discussion into a "Study of Factors Affecting Student Attitudes Towards Science".

During this evolution the overall concept of the study has not changed. The basic concern of the study from its inception has been to use the knowledge, in-sights and techniques of the social sciences to isolate and examine the factors which influence the attitudes of students towards the natural sciences. The explicit hypothesis, as formulated by McNarry and O'Farrell, is:

"Young people tend to view modern science and tech-nology as either the cause of. or a strong contributing factor to. many of society's current troubles. Conse-quently they tend to reject the natural (physical) scien-ces and instead have turned to the arts, humanit ies and social sciences. Declining enrolment trends in the physi-cal sciences may be used as a measure of this rejection".

It is the purpose of the study to examine this initial hypothesis; to modify it during the design phase of the study, to devise suitable instruments to test it and to validate the instruments in a pilot study.

By far the largest effort in science education to date, has been directed towards curriculum improvement and updating teacher qualifications. This investment, amounting to several hundred millions of dollars in the U.S.A. , appears to have had a relatively small effect on the overall "swing away from science". It would, therefore, seem to be a prudent investment of time and money to attempt to determine the factors that lie behind the observed phenomenon of declining enrol-ments in the physical sciences. In particular, we need to know the situation in Canada.

That physics should be central in this phenomenon is probably due to both the fundamental nature of physics and the involvement of physicists in the appli-cations of science to activities of immense societal con-sequence, e.g. the release and use of nuclear energy.

Funding for the project has been limited to a $7,000 feasibility grant from the National Research Council (November 1969), and a $5,000 contract with the Science Council of Canada (December 1969) to pro-duce a detailed proposal for a study of "How science is currently viewed in Canadian Society".

No further funds appear to be immediately avail-able from agencies such as the Canada Council, the Department of the Secretary of State, the National Research Council. The project cannot now be carried out as planned.

•See Physics in Canada. 25, 63 (1969).

76 / Physics in Canada

The critical path analysis for the Study indicates that the time available for funding at the time of writ-ing is only a few weeks, otherwise a delay of about 5 months will be introduced, even if funding is obtained after the end of March.

In the meantime the CAP Study Group is continu-ing to explore every possible means to obtain the necessary funding.

L. R. MCNARRY

C A P L O C A L S E C T I O N - O T T A W A A N D A R E A

A dinner meeting was held jointly with the Chemical Institute of Canada at the Sampan Restaurant on Tuesday, January 20th with 142 members and wives present. Dr. R. J. Uffen, Chief Science Adviser to the Cabinet, gave a very informative account of "The Evolution of Science Policy in Canada" which was followed by a stimulating question and answer period.

P L A C E M E N T S E R V I C E

Physicists looking for employment can fill the per-sonal information summary which appears as a separate page in this issue of the bulletin, and return it to: OPERATION RETRIEVAL, Department of Manpower and Immigration, 305 Rideau Street, Ottawa, Ontario.

P U B L I C A T I O N S C H E D U L E

Physics in Canada appears on January 1, March 1, May 1, July 1, September 1 and November 1 of each year. A special congress issue appears in late May. Members are invited to submit items for the sections on News, Canadian Physicists and the Calendar of Activities to the Associate Editor at the National Office, two months prior to the date of publication.

A D V E R T I S I N G R A T E S

The rates for advertising in Physics in Canada are as follows :

Full page $150.00 Half page 100.00 Quarter page 65.00 Back cover 175.00

Addit onal information can be obtained from P. C. Eastman, Advertising Editor, Department of Physics, University of Waterloo, Waterloo, Ont.

L I S T o F C A P " C O M M I T T E E S " 1 9 6 9 - 7 0

The following is a list of CAP committees, or the equi-valent of committees, along with the names of the cor-

ng chairmen. The eight subject Divisions and the Ottalwa Local Section of CAP are included in the list for t i e purpose of completeness.

1. Executive Committee : D. D. BETTS

2. Division of Theoretical Physics: N. L. GAUVIN

3. Div sion of Earth Physics: G. F. W E S T

4. Division of Medical and Biological Physics: P. M. BIRD

5. Division of Solid State Physics: J . F . COCHRAN

6. Division of Plasma Physics: R. A. NODWELL

7. Division of Nuclear Physics: G. c. NEILSON

8. Division of Physics Education: w. T H U M M

9. Division of Atomic and Molecular Physics: A. I. CARSWELL

10. Ottawa Local Section : D. A. RAMSAY

11. Nominating Committee: M. P . BACHYNSKI

12. Awards Committee: H. E. J O H N S

13. Editorial Board of Physics in Canada: D. E. BRODIE

14. Publications Committee: E. w. VOGT

15. Finance Committee: L . E . H. TRAINOR

16. Committee on Membership Accreditation: L. E. H. TRAINOR

17. Cotnmittee on Membership Campaign: A. BOIVIN

18. Annual Meeting - Programme Committee: E. w. VOGT

19. Annual Meeting - Local Organization: A. H. MORRISH

20. Committee on Science Policy: D. D. B E T T S

21. Cojnmittee on Summer Schools: A. BOIVIN

22. Copimittee on Placement Service: D. D. BETTS

23. Committee on the Constitution : N. L. GAUVIN

24. Committee on the French version of the Consti-tution: A. BOIVIN

25. Committee on High Energy Physics: E . p. HINCKS

26. Committee on Applied Physics: M. SAY 27. Cohimittee on a Division of Physics and Society:

J . F . COCHRAN

28. Committee on the 200 GEV Proposal: G. M. GRIFFITH

29. Committee on the 25th Anniversary. L . KERWIN

30. Committee on the Meeting of Corporate Mem-bers: E. w. VOGT

La Physique au Canada / 77

31. Committee on the Role of the Annual Meeting: C . C. M C M U L L E N

32. Committee on the Exchange of Scientific Equip-ment: L. K A T Z

33. Committee on the Educational Trust Fund: J. L. M E U N I E R

34. Committee on Student Affairs: M . W . J O H N S

35. Committee on Secondary School Physics Exami-nation: J. s. FRASER

36. Committee on Distinguished Lecture Tour: G. M. V O L K O F F

37. Committee on the brochure: "Physics. A Career. A Vocation": s. B. W O O D S

38. Committee on a Handbook of Graduate Oppor-tunities in Physics: p. R. SMY

39. Steering Committee: Socio-Scientific Study : L. R. M C N A R R Y

40. C A P Study Group: L . R. M C N A R R Y

41. Delegate to Youth Science Foundation: T. F. E M B L E T O N

42. Delegate to I U P A P : D. D. B E T T S

D I R E C T O R Y O F E M P L O Y E R S O F

P H Y S I C I S T S - 1 9 7 0

The 1970 edition of the Directory of Employers of Physicists, prepared by the Committee on the Place-ment Service, chaired by D. D. Betts, is available free of charge to CAP members and at $2.00 per copy to non-members.

M I S S I N G I S S U E S O F " P H Y S I C S I N

CANADA"

We are in the process of assembling complete series of Physics in Canada since its first year of publication. These would have to be ready for binding very shortly so that we may have them on time for our 25th Anni-versary celebrations in June. We are urgently request-ing anyone who can donate issues of Physics in Canada from 1945 through to 1957 inclusively to please forward them to the National Office. Merci.

Calendar / Calendrier June 17-19. Winnipeg

4th Annua l Congress of the Canadian Meteorological Society, ( j . MAYBANK. Program Chai rman, Saskatch-ewan Research Council , Saskatoon, Sask.)

June 2 2 - 2 3 - 2 4 - 2 5 , Winnipeg Annual Meeting. Joint Meeting of CAP with the American Physical Society and the Sociedad Mexi-cana de Fisica. (E. w . VOGT, Depar tment of Physics. U.B.C. )

August 16-28, Banff Summer School organized by the Division of Nuclear Physics and the Division of Theoretical Physics of CAP. (G. c. NEILSON. Nuclear Research Center , Uni-versity of Alberta. Edmonton . Alta.)

August 24-Sep tember 5. Alta Lake, B.C. NATO Advanced Summer Institute on Magnetism in Rare Earth Materials, (R. R. HAERING. Depar tment of Physics. Simon Fraser University, Burnaby 2, B.C.)

October , Edmonton Sixth Annual Undergraduate Physics Conference or-ganized by the Canadian Undergraduate Physics Association.

Books Received The following books have been received recently for review. Space will not permit reviews of all these to be published. Anyone interested in having a part icular book reviewed or in writing a review please communica te with the Book Review Editor. G . E. Reesor, University of Waterloo. Magnetism and The Atom. P. GRUICH, Exposition

Press, 1969. Pp. 24, Price: $3.00 Axiomatization of the Theory of Relativity. HANS

REICHENBACK. University of Cal i fornia Press. 1969. P p . 2 0 8 , P r i c e : $ 7 . 9 5

Men of Physics. Kark Lark-Horovitz (Pioneer in Solid State Physics). V. A. JOHNSON, Pergamon Press, 1969. P p . 2 8 9 , P r i c e : $ 6 . 0 0

Vtli International Congress on A'-Ray Optics and Micro-analysis. G . M O I . L E N S T E D T a n d K . A . G A U K L E R , Springer-Verlag, 1969. Pp. 612, Price: $54.50

Advances in Plasma Physics. S I M O N a n d T H O M P S O N (ed i tors ) , John Wiley & Sons. Vol. II. Pp. 211, Price: $ 1 3 . 5 0 , V o l . I V . P p . 2 4 9 , P r i c e : $ 1 4 . 9 5

The Ocean, (Scientific American Book). W. H. FREEMAN, 1 9 6 9 . P p . 1 4 0 . P r i c e : $ 6 . 5 0 ( $ 3 . 2 5 p a p e r b o u n d )

Experimental Neutron Thermalization. P. A. EGEI.STAFF and N . J. POOLE, Pe rgamon Press, 1969. Pp. 399, P r i c e : $ 1 7 . 5 0

Studies in Statistical Mechanics (Vol. IV) The Maxwell Equations. J. H . DE BOER, John Wiley & Sons, 1969. P p . 1 7 9 , P r i c e : $ 8 . 9 5

Advances in Chemical Physics (Vol. XVI). S. A. RICE and I. PRIGONINE, John Wiley & Sons, 1969. Pp. 419. P r i c e : $ 2 1 . 0 0

Topics in Advanced Math for Electronics Technology. S. P A U L L , 1 9 6 9 . P p . 4 2 0 , P r i c e : $ 1 5 . 0 0

Thermal Physics. G . KITTEL, John Wiley & Sons, 1969. P p . 4 1 8 , P r i c e $ 1 0 . 9 5

Gallium Arsenide Lasers. C. H. GOOCH, John Wiley & Sons, 1969. Pp. 333, Price $14.50

78 / Phys ics in C a n a d a

Cosmic Electrodynamics. J. H. PIDDINGTON, John Wiley & Sons, 1969. Pp. 305, Price $18 .50

Elementary Excitations in Solids. A . A . MARADUDIN and G . F. NARDELLI, Plenum Press, 1969. Pp. 526, Price $ 3 5 . 0 0

Lecture Notes in Physics - Vol. 1. W a r m e l e i t u n g in Kris t -allen, Theoretische Grundlagen und Fortgeschrittene Experimentelle Methoden, J. C. ERDMANN, Springer-Verlag, 1969. Pp. 283, Price $5.50

Lecture Notes in Physics. Vol. 2. T h é o r i e de la renor -malization. K. HEPP, Springer-Verlag, 1969. Pp. 215, Price $5.00

Lecture Notes in Physics. Vol3. Scat ter ing T h e o r y : Un i -tarity, Analyticity and Crossing. ANDRÉ MARTIN, Springer-Verlag, 1969. Pp. 125

Physics In My Generation. MAX BORN, Springer-Verlag, 1969. Pp. 172, Price $3.80

Codata, International Compendium of Numerical Date Project. MARTIN LEWIS, Springer-Verlag, 1969. Pp. 295

Low Frequency Waves and Irregularities in the Iono-sphere. Edited by N. D. ANGELO, Springer-Verlag, 1969. Pp. 218

Progress in Quantum Electronics. Vol. 1. Light P ropaga -tion and Light Shifts in Optical Pumping Experiments. J. H. SANDERS and K. W. H. STEVENS, Pergamon Press, 1970. Pp. 103, Price $3.25

Cosmic Ray Physics. S. HAYAKAWA, John Wiley & Sons, 1969. Pp. 114, Price $39.50

Book Reviews LES PROPRIETES ELECTRONIQUES DES COUCHES MINCES, Presses Universitaires de France, (1969) pp. 165, $7.00

Cette publication de 165 pages est reliée de la même façon que les exemplaires mensuels du Journal de Phy-sique-, elle constitue en fait un supplément aux numéros 2 et 3 du volume 29 de ce Journal (février-mars, 1968). Dans ce supplément se trouvent les 22 exposés présentés au colloque de la Société Française de Physique qui s'est tenu à Orsay les 22 et 23 juin, 1967.

Le Congrès a été d'une nature plus technique que ne le suggère son titre. Tous les exposés, à l'exception de trois, (les phénomènes de transport en surface dans les semi-conducteurs, les propriétés optiques et de transport des couches minces de cuprite, et la magnétorésistance dans une couche électronique d'inversion sur une surface de silicium), concernaient les métaux. La majorité des exposés, se rapporta aux sujets suivants: - Les couches magnétiques (y compris celui de Néel sur

les parois dans les films minces (8 pages), celui de Wade sur la microscopie électronique des structures des domaines (15 pages)).

- Ondes de spin dans les couches minces magnétiques (y compris une revue (13 pages) par Berteaud):

- La superconductivité (y compris une revue (13 pages, 69 sources citées) par J. Clarke se rapportant à des expériences sur l'effet de proximité entre une couche mince normale et une superconductrice).

- Propriétés de transport en général, y compris les effets

dimersionnels (par exemple une revue de 12 pages par Abelès sur les propriétés de transport des couches mincels). Les exposés, ont été faits en français (à l'exception de

3 en anglais) et proviennent de laboratoires situés en France (sauf un exposé provenant d'Angleterre et un de Hollande).

Cette ipublication devrait être sur les rayons des biblio-thèques de chacune des organisations qui se consacrent au travail des couches minces (et devrait être classée avec d'autres fascicules du Journal de Physique). Dans la négative, il faudrait acheter un exemplaire qui coûterait, en moyenne, 4 cents la page.

L. D. REED, UNIVERSITE LAUREN TIEN NE

ADVANCES IN NUCLEAR PHYSICS. Vol . 1, ed by Michel Barangèr and Erich Vogt. P l enum Press, 1968. Pp . 416 . $18.50 U.S.

This is the first volume of a series the aim of which is to provide review articles which "chart the field of nuclear physics with some regularity and completeness". The basic viewpoint of the series is pedagogical with the em-phasis qn physics rather than theoretical or experimental techniques.

There are five articles in this volume: (1) "The Re-orientation Effect" by J. de Boer and J. Eichler, (2) "The Nuclear SU3 Model" by M. Harvey, (3) "The Hartred-Fock Theory of Deformed Light Nuclei" by G. Ripka, (4) "The Statistical Theory of Nuclear Re-actions" by E. Vogt, and (5) "Three-Particle Scattering - A Review of Recent Work on the Non-relativistic Theoryf' by I. Duck. As one would guess from the titles, all except the first deal with theoretical topics.

Thes|e articles are all well written. Each contains ample introductory material and a good bibliography with references up to 1967. Most technical details have been either rtmitted or placed in appendices. A senior graduate studenlj in nuclear physics should have little difficulty with articles (1) to (4), although article (5) could present some problems owing to its somewhat esoteric subject material.

Researchers wishing to keep well informed on aspects of the field other than their speciality should find these articles extremely useful. They are also highly recom-mended to those wishing good introductory material on the various topics before attacking the more detailed literature.

R. J . TURNER, TORONTO

MECHANICS, by Ray Skinner. Blaisdell Publishing Co., . $14.50. pp. 774

This book constitutes the first volume of a planned set of five books on undergraduate physics for students major-ing in Science or Engineering. This volume is designed to cover Newtonian mechanics in an introductory course of fouf or more semesters.

The topics covered are kinematics (including an intro-

La Physique au Canada / 79

duct ion to vectors and calculus) , particle dynamics, con-servation laws, rigid body motion, scattering, and a long chapter on waves including an introduction to Four ier series. T h e book contains a much more extensive discus-sion on inertial reference f rames , their propert ies and availability, than other introductory books commonly used. T h e principle of equivalence is introduced and used to discuss the application of Newton ' s Laws in non-inertial f rames .

T h e approach used by the au thor is mathematical as opposed to phenomenological . Existence and uniqueness theorems for differential equat ions are discussed and are then used to show that the second law combined with a set of initial conditions determines motion in the future . The conservation laws are established using the concepts of homogenei ty of t ime and space and the isotropy of space. The re are many examples and problems inte-grated into the text and answers are given in the back of the book. Most of the problems are of a routine nature and the level of difficulty is not too high.

In summary I feel that the mathemat ical and relatively abstract approach to int roductory physics used by the au thor makes the book unsuitable fo r use in a first course in physics. Also, the book is very lengthy and quite expensive for use in any single course.

T h e book, however, is careful ly and clearly written and the extensive discussions on many subjects will make worthwhile reading for most students and teachers.

J . c. I R W I N , S.F.U.

PRACTICAL W O R K IN E L E M E N T A R Y A S T R O N O M Y , by M. G. J. Minnaert. Springer-Verlag New York . Inc., New York. Pp. xxiv + 247. $9.20.

Prof. Minnaer t is a distinguished as t ronomer at the Utrecht Observatory. H e has also been, fo r many years, a s trong advocate of the teaching of as t ronomy as a discipline in its own right, al though, of course, coupled with a solid background of physics and mathematics . To Prof . Minnaert , practical instruction is an essential part of any as t ronomy course, fo r he shares with many as t ronomers the belief in the impor tance of the "fee l" for the subject that can only come f rom direct observation. This book is a distillation of his teaching experience over 25 years at Utrecht . It is primarily aimed at f reshmen physicists, as t ronomers and mathematic ians . Because, in most English-speaking countries, as t ronomy is rarely taught as such in schools, the book contains some simple experiments of the constellation-recognition type. But, lest the word "e lementary" be misconstrued, it should be emphasized that the book also contains sophisticated experiments such as the determinat ion of the curve of growth of a stellar spectrum, calculations on the three-body problem, and the spiral s t ructure of the Galaxy f rom 21-cm line observations, topics that would not nor-mally be considered fo r the sophomore , let alone the f r e shman year at universities on the American continent.

T h e very breadth of the selection of experiments does, perhaps, make the book ill-matched to most courses of

practical as t ronomy on this continent, since a sophisti-cated experiment or observational reduction should be under taken only when the basic theory has been dealt with in lectures. However, fo r an instructor planning a practical course in as t ronomy, at any level in the univer-sity, this book is a mine of valuable suggestions, and useful hints on organization and teaching techniques. Part icularly interesting are the descriptions of various simple pieces of apparatus, such as a students ' microden-sitometer, which can be made in numbers by a normal all-purpose depar tmental workshop. While the student should be exposed to the potentialities for accurate measurement of modern instruments (even if they be only "black boxes" to him. there is also much value to the student in handling very simple, easily-understood, instruments as well.

N o one who is responsible for the teaching of astron-omy at a university could fail to find this a most st imulating book.

M I C H A E L W . O V E N D E N , U . B . C .

F I E L D S A N D / O R PARTICLES, by D. K. Sen. Academic Press Inc.. London. Pp. 1 39 + x. 5()S.

It is not surprising that physical theories to explain basic phenomena such as gravitation, electricity, should involve concepts such as "wave" and "particle". In the world of every day experience it seems that energy and momen tum can only be transmitted f rom one point to another by "shaking the med ium" or by the t ransfer of matter , and the equations devised to describe the events occur r ing in nature have stressed one or o ther (or both) of these modes of activity.

It is a valuable contr ibution to the student of physics to see an examinat ion of the various theories and a classification of them in terms of the extent to which they lean on one or other of these concepts. But the au thor has done more than this - he gives the theories themselves ( in summary f o r m ) and comments on their successes and failures. The presentation is designed to display the essen-tial s t ructure of each theoretical edifice, calling part icular attention to elements in the structure which seem defec-tive for one reason or another . The hope of theorists appears to have been to escape f rom the field-particle duality (i.e. to clarify, to the point of i l lumination, the relationship between the field and its source) , and the extent to which this has been achieved is clearly displayed in this book.

The fact that so many important theoretical methods are presented in the short space of a few pages is one of the useful features of the book. Of course this involves great condensation and requires the reader to proceed slowly, but anyone competent to read the book with profit should have no trouble whereas the graduate stu-dent would develop excellent skills in struggling with the subject matter . The story unfolds logically and with clarity and the book can be recommended either for a quick reading by a person of experience or for serious study by a student.

w . J . ARCHIBALD, DALHOUSIE

80 / Physics in Canada

DIGITAL ELECTRONICS FOR SCIENTISTS, by H.V. Malm-stadt and C. G. Enko, W. A. Benjamin (1969) pp. 545, $10.75

It was a pleasure to read this well written text in which the authors have covered in a logical sequence a vast amoun t of material ranging f rom Boolean algebra to the organization of the digital computer . All the basic circuits; gates, flip flops, memories, counters etc. and a number of advanced examples of analogue to digital systems such as the digital vol tmeter are very clearly explained with a minimal amount of mathematics . The only prerequisite to appreciate this text is a knowledge of electronic devices and although the authors have tried to overcome this problem by spending about two chapters reviewing diodes, transistors, SCR'S relays and optoelectronic switches, I fear that their t reatment may not be adequate for the newcomer to electronics. The last one-third of the book describes, in detail, experi-ments illustrating the principles and circuits discussed in the first two-thirds of the text. The appara tus for these experiments has been specially developed in con-venient modular fo rm by the Heath Company but many of the experiments, in part icular, the easier ones could be carried out with equipment available in most elec-tronic laboratories.

The introduction of cheap integrated circuits in the last few years has made digital techniques both econo-mically and technically feasible for use in research lab-oratories and this text is ideal fo r teaching the basic principles and circuits.

H. J . SMITH, UNIVERSITY OF WATERLOO

TYPE N SUPERCONDUCTIVITY, by D. Saint-James, G. Sarma and E. J. Thomas, Pergamon Press, 1969, pp. 294. $14.00

Type it Superconductivity has stimulated a t remendous amoun t of interest over the last decade and books which consolidate and review the present state of knowledge are sorely needed. This book helps to fill that need.

T h e work is divided into two sections called Revers-ible Propert ies and Irreversible Properties. The first is primari ly theoretical, the second essentially experi-mental . Al though the material covered in the two sec-tions could very nicely have been juxtaposed to form a single volume, the t reatment in the two parts is so dif-ferent that it would have been better to publish them separately.

One is tempted to compare the first part which was written by D . Saint-James and G . Sarma with the de Gennes text but one finds that the fo rmat is more conventional. The t rea tment is sufficiently different to consider the text as a distinct and worthwhile contribu-tion. particularly in view of the extensive discussion of properties of superconductors in high magnetic fields,

surface superconductivity, gapless superconductivity and thermal properties.

The se cond part by E. J. Thomas is not only marred by proof reading errors (p. 209) which the publisher should htive caught but it also contains unfor tuna te slips such as "Coulomb forces between flux lines" (p. 228) and confusion between potential difference and electric field (p . 2 3 1 ) . The author has been somewhat uncriti-cal in his selection of experimental data and in his dis-cussion of many of the remaining problems. For ex-ample, his discussion of the Hall Effect could have out-lined thç controversy over the mechanism. Instead he gives a \ e r y sketchy account which is confused by intro-ducing guided motion.

Although this reviewer believes the second part is of limited Value to either the scientist who wants to gain an insight into the physics of flux motion and spinning or to one who is interested in applications, the book as a whole ranks as a significant contribution to the field.

P. P. MEINCKE, UNIVERSITY OF TORONTO

THE NEW COSMOS, by Albrecht Unsold, Springer-Verlag, New York Inc. ( 1 9 6 9 ) , pp. 373, $7.00

T h e study of the Universe beyond our planet has prob-ably never before attracted so much critical attention f rom sqientists. At one time knowledge of current ob-servations and theories in as t ronomy would have been basic to a scientific education. The flow of new results, interpretations and techniques in all fields of astro-physics is now too overwhelming for most astrophysi-cists to contend with. There are probably few who could succeed in giving a comprehensive perspective of the subject at a satisfactory scientific level for chemists, physicists and mathematicians. Professor Unsold has none the less been very successful in doing just that in this book which is a translation of his "Der Neue Kosmos" . It is divided into three parts, Classical Astron-omy, Sun and Stars, and Stellar Systems. T h e latter in-cludes discussions of Cosmogony and Cosmology. He assumes a good background in physics and mathemal ics for his readers but gives a thorough introduction to the basic concepts of astrophysics used in each section. Each topic is put in its historical context and there is a critical appraisal of the observational techniques in-volved. The excellent translation is by W. H . McCrea and the text is both clear in content and lay-out. There are 137 figures and an extensive index and bibliography. The book is something more than an introduction to astrophysics for those who would like to continue seri-ous study or research in the subject. It is an excellent refresher course for those long committed to aslro-physici and it penetrates particularly in the later chap-ters to the basic, more philosophical questions which are thç fundamenta l stimulus for the rest of the book.

G. A. H. WALKER, UNIVERSITY OF BRITISH COLUMBIA

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Joint Summer

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Winnipeg, Manitoba

22-25 juin 1970

What is a Nim-Standard

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A Scimitar is a trusty companion, / ^ ^ ^ ^ ^ simple yet sturdy in design. Constructed as a precision instrument, it is / r e w a r d i n g l y easy to use. The clean lines conceal a wealth of engineering artistry in the tempered selection and use of materia s. Scimitars accompany prudent explorers on exotic journeys of discovery. The complete line made by Simtec conforms to NIM-standards ^ ^ ^ ^ set byAEC20893 and was developed in co-operation i ^ ^ ^ H S l l T l t ^ O l t C l with AECL Chalk River Nuclear Laboratories. It is >1 • • ( • U H l ^ S T m W U ' i

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