UNCLASSIFIED

UNCLASSIFIED

RIB-9

Subject Category: INSTRUMENTATION

UNITED STATES ATOMIC ENERGY COMMISSION

SCINTILLATION CRYSTALS

Progress Report for Period January 1, 1956 to April 1, 1956

ByRobert Beadle

April 25, 1956

Engineer Research and Development Laboratories Fort Belvoir, Virginia

Technical Information Service Extension, Oak Ridge, Tenn.

LEGAL NOTICE

This report was prepared as an account of Government sponsored work. Neither the

United Sfates, nor the Commission, nor any person acting on behalf of the Commission:

A. Makes any warranty or representation, express or implied, with respect to the ac curacy, completeness, or usefulness of the information contained in this report, or that the

use of any information, apparatus, method, or process disclosed in this report may not in

fringe privately owned rights} orB. Assumes any liabilities with respect to the use of, or for damages resulting from the

use of any information, apparatus, method, or process disclosed in this report.

As used in the above, "person acting on behalf of the Commission" includes any em ployee or contractor of the Commission to the extent that such employee or contractor prepares, handles or distributes, or provides access to, any information pursuant to his em

ployment or contract with the Commission.

This report has available copy.

been reproduced directly from the best

Printed in USA, Price 20 cents. Available from the Office of Technical Services, Department of Commerce, Wash ington 25, D. C b

AEC, Oak Ridge, Tenn.

RIB-9

MATERIALS BRANCH ENGINEER RESEARCH & DEVELOPMENT LABORATORIES

U. S. ARMYFORT BELVOIR, VIRGINIA

25 April 1956

PROGRESS REPORT ON AEC CONTRACT Oil RESEARCH AND DEVELOPMENT PROGRAM

ON SCINTILLATION CRYSTALS

Period 1 Jan 1956 to 1 April 1956

Submitted by: Approved by:Robert Beadle Arthur W. Van HeuckerothChemistry Section Chief, Materials Branch

This work was performed for the Radiation Instruments Branch, Division of Biology and Medicine, U. S. Atomic Energy Commission, Washington, D. C.

ABSTRACT

This report covers the preliminary literature survey

and the screening of activated cesium iodide and several

alkali halides to qualitatively determine their luminescence,

The crystals or powders were excited by 2$37 A U, V. or

3660 A U. V. light and the fluorescent and phosphorescent

light emission visually observed. Those materials exhibiting

a strong fluorescence will be later quantitatively

evaluated.

The report also includes a proposal pf future work and

a proposed budget for the 195? fiscal year*

PROGRESS REPORT ON A. E. C. CONTRACT -ON RESEARCH AND DEVELOPMENT PROGRAM ON SCINTILLATION CRYSTALS

Period 1 Jan 1956 to 1 April 1956

^» Purpose* The purpose of this research as outlined ift the original proposal is the investigation of inorganic materials of high 2 and low re fractive index for use as scintillation crystals for detection of nuclearradiation.

II. Background. The following table summarizes the efficiencies and Z number for most of the important inorganic scintillators generally used in detectors:

Crystal Conversion Efficiency Density, g/cm^

Nal (Tl) lOJg 3.67Cal (Tl) 7.5 U.50Kl (Tl) 2 3.13Rbl (Tl) 2 3,5$ Lil (Tl or Sn) Thermal Neutrons U.06Ca WQK 5 6.06Cd Wbjj 10 7-90

Tables I-X taken from the literature list most of the inorganic crystals studied by various investigators and the pertinent data obtained relative to their use as scintillation crystals* The following biblio graphy has been prepared to include primarily the work previously done on scintillation crystals* Many of the references are reviews or books which in themselves contain extensive bibliographies* A continuing study of the literature is being made to better understand the mechanism of the scin~ tillation process and keep abreast of new developments in the field,

ni- Method, It is the intent of this research to evaluate all feasible materials, witii or without activation for scintillation charac teristics, The initial phase of this work will be a screening program using 2537 A and 3660 A U. V. light to excite the material to lumines cence. Those materials exhibiting a strong fluorescence will be studied further for relative peak height, decay time, energy response, light emission and efficiency.

Cesium iodide was selected as a starting host material because of its high Z components and ease of crystallization. Hofstader (li,5) reports Csl (Tl) to be about 75/S as efficient as Nal (Tl) . It was

also the opinion of Smakula x and Van Sciver # that properly activated Csl prystals might exceed the efficiency of Nal (Tl). Discussions held with G. F* V. Garlick, University of Birmingham-and R. ,B..Owen, A. E. R. E. Harwell, England indicated that cesium iodide, highly purified and suitably activated merit investigation. Also Dr. Garlick suggested cadmium fluoride, magnesium fluoride and cadmium iodide might prove interesting and worth investigating.

IV. Experimental

! The cesium iodide used was analyzed spectrographically and found to be approximately 99.7$ pure containing traces of aluminum, chro mium, copper, iron, magnesium, potassium, sodium and rubidium* Further purification of this cesium iodide is in progress but not completed at ^his time. Recently cesium iodide of 99*9% purity has been obtained and is being used for comparative purposes. The cesium iodide was activated with 0.1$ by weight of the activator element. The components were inti mately mixed by grinding, melted in either fused silica or Vycor vessels and cooled in air.

The resulting crystalline mass was examined under 25>37 A and 3660 A U.V, light and the fluorescence and phosphorescence visually ob served. If no long persisting phosphorescence was observed the material was listed as fluorescent, if phosphorescence was observed it was noted. As fluorescence and the scintillation process are a similar phenomena, those compounds exhibiting fluorescence will be studied further for rela tive peak height and decay time.

The method of Bridgman as modified by Stockbarger was used to grow small crystals (1/2" diameter) of Csl (Tl), Csl (Mn) and Csl (Cu).

2. Table XI contains a summary of the materials examined, the activator, the salt of the activating element used, and the visual light emission characteristics.

Table XII contains a summary of the three activated cesium iodide crystals grown. No quantitative measure of the degree of fluores cence was made at this time as the response to nuclear radiation will be more definitive,

V. Re suit s» The work covered in this report has not progressed far enough to establish or predict any new scintillation materials. The screening phase does indicate several of the activated cesium iodide materials merit further study. These are the Cu, Co, Mn, Hg, Cd, W and As activated materials.

VI. Future Program and Proposed Work for FY 1957*

1. The screening program will be continued in attempt to

* Private communication.

activate to luminescence materials such as barium fluoride, cadmium fluo ride, magnesium fluoride, cadmium iodide, calcium iodide, thallium chlo ride, lithium fluoride and iodide, lead fluoride and chloride, etc.

2. Suitable techniques will be investigated to produce small crystals for pulse height and decay time measurements.

3. Equipment is being assembled consisting Of a beta source, crystal and necessary colligation coupled to^ a DiMont 6292 photpmultiplier tube and a suitable oscilliscope. The scintillation: characteristic of the materials will be compared to anthracene using a beta source. Any material having a relative peak height of 2J>-£0$ that of anthracene will be studied in great detail*

iu If work progresses far enough, techniques for growing single crystals of the most promising materials will be investigated. Such crystals will be necessary for final quantitative measurements.

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TABLE II

FLUORESCENT AND STIMUIATION PROPERTIES OF CRYSTALS (7)

Crystal

NaCl -i AgCl, \%

Nad + AgCl, \%

NaCl + AgCl, 5$

Csl + Tl #A

Csl + Tl #1

CsBr -f- Tl

KC1 + AgCl

KBr * TlBr, ^

NaCl + Cud, 1$

LiP -t AgCl

CaF

Effective Emitted Fluorescent Stimulated Mass, gs Wavelength Intensity Compared Intensity

to Anthracense by Same Mass 1 min. U.V.

6.5 U.V.

6.5 U.V.

5.7 u.v.

9Ji Bl. Or.

11.0 Bl. Gr.

11.0

10.0

5.7 Near U.V.

5.7

5.7

2 Far U.V.

1.0 56

1.8 27

0.8 20

1.1

1.3

3.0

<0.1 0

1.7 ~U

0.1 --I

0.02 --0

0.7 *1

Crystals irradiated with gamma radiation and stimulated with 3600 A U.V. radiation.

TABLE III

RELATIVE PEAK VOLTAGES FOR VARIOUS SUBSTANCES (7)

Substance

Single crystals

Anthracene

Stilbene

Naphthalene

Kl (Tl)

CsBr (Tl)

K Br (T3)

Csl (Tl)

NaCl ($% AgCl)

NaCl (1$ AgCl)

Powders

ZnS long persistent Ag

ZnS short persistent ZnCd

ZnO

Gamma Ray Irradiation

U2

51

17

13

19

11

20

7

27

12

0

Alpha Particle Irradiation

57

5U

31

U3

U3

2U

88

280

175

25

Noise

Uio

3UO

60

Wavelength of Max. Emission

UUUo £

Uioo

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Uioo

5300

-UUoo

Relative Ray Pulse Ht.

100

60

U8

210

12

75

\ to /# Ratio, %

9

9

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kU- 93

-95

10

TABLE IV

EFFICIENCY OP SEVERAL SCINTILLATORS (8)

Scintillator

Anthracene crystal

Stilbene crystal

Xylene t 5 g/1 terphenyl t- 0.01 g/1 diphenyl hexatriene

Nal (Tl)

Lil (Sn)

Lil (Eu)

100 gms polyvinyl toluene t-h gms terphenyl + O.lg diphenyl-stilbene U8 9

TABLE V

RELATIVE PEAK VOLTAGES FOR SCINTILLATION CRYSTALS (9)

Crystal Decay Mico Sec. Peak Voltage

Nal (Tl) 0.25 100

Csl (Tl) 1.1 t 0.1 22

KC (Tl) 7i.o 19

Anthracene 0.023 t 0.005 52

CsBr (Tl) Not measured 10

Stilbene 0.006 0.001 26

Lil (Tl) 1.2 8

Lil (Tl) 1.2 ± 0.1 8

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0.23

0.12

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12

TABLE VII

(12)

Phosphor Activator EfficiencyFast

Electrons

Slow Electronsor

Soft X-ray

ZuS

ZnS

CdS

ZnS/CdS

CaWOu

KBr

CSBr

Csl

KI

LIP

NaCl

Nal

Anthracene crystal

Anthracene powder

Diphenyl

Ag .0..28

Cu 0.25

Ag 0.23

Cu 0 .12

0.017

0.017

Ag Cl

Ag CL

Tl

0.011

0.006

0.0027

0.135

0.22

0.23

0.18

0.08

0.07

0.23

0.06-0.16

0.02-0.09

0.0055

0.126

0.08-0.22

0.10

0.09

0.031

0.20

0.30

0.15

0.12

O.OU

Phosphor

Naphthalene

Anthracene

Phenanthrene

Terphenyl

Stilbene

Nal (Tl)

KI (Tl)

Csl (Tl)

Lil (Tl)

13

TABLE VIII

FLUORESCENT DECAY TIMES (12)

Gamma Excitation

Dee-ay time x 10"9 Sec

57-87

23-35

8-12

U-12

U.U-12

250*

1000*

1000*

1000*

ZnS (Ag)

Alpha Excitation

1000*

#Decay roughly exponential

TABLE IX

ALKALI HALIDE PHOSPHORS (13)

Phosphor Light Conversion Efficiency (Approx,

Nal (Tl)

H (Tl)

Lil (Tl)

Csl (Tl)

CsF

Ca¥0U

CdWOi.

0.08

0.02

0.01

0.06

0.003

>0.05

0.10

Density , ) gm/cc

3.67

3.13

U,06

U.50

3.59

6.12

7.90

Melting Point Decay C Sec.

651 2.5 x 10-7

582 >10"6

Ul*6 >10"^

621 >10-6

5 x 10-9

~o.5 x 10*6

0.5 x lo"6

This data taken in part from tables in Scintillation Counters, J, B« Birks

Crystal

Activator Concentration, mole %

Color fluorescence

Appearance daylight

Relative pulse ht,, with CS^? and Nal(Tl)

Decay time, per sec

Stability of crystal after canning

TABLE X

Lll(Sn) Lil(Eu) Lil(Sm) Nal(Tl)

l»o.o5

Green

Yellow green

7,5

0.8

Affected by

0.03

Blue

35

1.U

Stable

0.02

Blue

Colorless

3.3

0.25

Deteriorates

0.05

Blue

Colorless

100

0.3U

Stableradiation under

radiation

15

TABLE XI

SUMMARY OF THE LUMINESCENT PROPERTIES OF ACTIVATED CESIUM IODIDE

CompoundActivator Element Salt, 0.1 % Wt.

CslCsl (Tl)Csl (In)Csl (In)Csl (Ga)Csl (Sn) 3 si (Od)Csl (Ag)Csl (Cu)Csl (Mn)Csl (Ce)Csl (Sn)Csl (Pb) Csl (Ni) Csl (Co)Csl (Te)Csl (Ti) Csl (Sb)Csl (Bi)Csl (Zn)Csl (Sr) Csl (Ba)Csl (Cu)Csl (Co)Csl (Ca)Csl (Hg)Csl (Mn)Csl (Mn)Csl (As)Csl (¥)Csl (Ba, Cr)Csl (Bi)Csl (Cu)BaCl2(lln) KI (Tl)KBr (Tl)KC1 (Tl)Nal (Tl)

TilIn MetalIn(NO)3 Ui H20Ga(H03)3Sm(N03 ) 3 6 H^O Cd I 2AglCu SOL 5 H 20MnSC-LCe02Sn ClPbI2 & C1 2 Ni (N03 ) 2 Co MetalTe MetalTi2 3 SbTSetal, 1%Bi Metal, ~L%Zn Cl?Sr(N03 ) 2 Ba C1 2Cu C1 2Co C13 6 H 20Ca SOLHg I 2Mn 02 ) 1%Mn0 2-0.01$AsoO-j¥0)|Ba CrOhBi(N03)3 .5H 20CuOMnSO. TilTl BrTl ClTil

Light Buission 2537A————————3660A

White Fl NoneWhite Fl -NoneWhite Fl NoneWhite Fl NoneNone NoneNone None Pale cream orange Fl NoneNone NonePale Blue NoneGreen NoneBlue White, yellow NoneNone NoneNone NoneNone NoneNone NoneNone NonePale Yellow NoneNone NoneNone NoneNone NoneNone Nonef * Yellow white Fl NoneLt Blue & Pink Fl NonePale blue Fl NonePale yellow Fl None Pale cream yellow Fl NoneBlue Green Fl NonePale blue Fl NonePale yellow Fl NoneBlue white Fl NoneYellow green Fl NoneNone NonePale Blue Fl NonePale pink Fl NoneViolet Fl NoneViolet Fl NoneCream Fl NoneBlue Violet None

Remarks

Phos Phps

Phos

Phos Phos

Phos Phos Phos

good lightPhos

Phos Phos

16

TABLE XII

SUMMARY OF ACTIVATED CESIUM IODIDE CRYSTALS

Crystal %_Wt. Activator Ron arks

Csl (Tl) 1+Q% Til Crystal exhibited whitefluorescence under 2537 A U.V. light, crystal appeared to be single

Csl (Hn) • l.OJg Mn SO^ Crystal exhibited yellow whitefluorescence under 2$37A U.V. light, crystal was browned and opaque

Csl (Cu) 1.0J6 Anhyd* Cu SOj^ Crystal exhibited pale bluewhite fluorescence under 2537 A U.V. light, crystal was dark in color and opaque

In all three crystals there was an excess of the activator at the top of the crystal*

17

BIBLIOGRAPHY

1, Latest Developments in Scintillation Counting Nucleonics 10 , No. 3* Q-952)

2 % Solid and Liquid Scintillation Counting, George T. .Reynolds, Nucleonics 10 No, 7

3% Characteristics of Scintillators, Robert K. Swank Annual Review of Nuclear Science U,, 111-50

U, Detection of Nuclear Particles, W. H. Jordan, Annual Review of Nuclear Science 1, 207-iiO (1952)

5c Hofstader, R. Nucleonics 6, No. 5, 70 (1950)

6. Jordan, W. H«, Bell, P. R. Nucleonics 5 No. U, 30 (19U9)

7. Bittman, L., Furst, M., and Kallman, H., Physical Review, 87, 83 (1952)

8. Recent Advances in Scintillation Phosphors, Theory of, Robert K. Swank, Nucleonics 12, No. 3 (195U)

9. Preparation and Perfomance of Some Scintillation Crystals, J* A. Harshaw, H. C. Kremers, E. C. Stevrart, £• K. Warburton, J* 0. Hay, Sept 10, 1952, N.Y.O. 1577

10. Hofstader, R., physical Review ?U, 100-1 (19li8)

11. Luminescence and the Scintillation Counter, S. C. Curran, Academic Press Inc'.j 1953, Mew Yoik

12. Electron and Nuclear Counters, Korf, S. A., D* Van Nostrand Co., Inc., 2nd Edition 1955

13. Scintillation Counters, J. B. BLrks, McGraw-Hill Book Co., Inc. 1953

lU. Moon, R. J, Physical Review 73, 1210, 19U8

15. Luminescence with Particular Reference to Inorganic Phosphors, British Journal of Applied Physics Supplement No. U3 1955

16. Luminescent Efficiency of Large Crystals of Ca WOi , and Cd WOi , Paul W. Levy, Contract N onr-230(00) NP-536?

17. Scintillation Phenomena in Nal and CsF, Wesley V. Van scriver, April 1955 Contract N6-onr-25ll6

18. The ̂ Luminescence of Alkali Halides, Activated by Heavy Metals - Final Report July 1, 1952 - Dec. 31, 195U, Alien B. Scott, Contract DA-OU- 200-ORD-132 (NP-5505)

18

19. Luminescence of Solids, Humboldt W. Leverenz, John Wiley and Sons-, Inc., New York, 1950

20. Some Lithium Iodide phosphors for Slow Neutron Detection 'British Journal of Applied Physics 6, 10U-6 (1955)