Download - Chapter 27 Nuclear Physics

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PHYSICS

PHYSICS

NUCLEAR

PHYSICS

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

NUMBER LEARNING OUTCOME

i U n d e r s t a n d t h e s t r u c t u r e o f t h e a t o m .

ii L e a r n t h e s i m p l e m o d e l o f t h e m o d e r n a t o m .

iii U n d e r s t a n d t h e d i f f e r e n c e b e t w e e n t h e t e r m s p r o t o n

n u m b e r a n d n e u t r o n n u m b e r.

iv L e a r n w h a t a r e n u c l i d e s a n d h o w a r e n u c l i d e s r e p r e s e n t e d .

v W h a t a r e i s o t o p e s ?

vi U n d e r s t a n d n u c l e a r p r o c e s s e s i n t e r m s o f w h a t i s

c o n s e r v e d .

vii L e a r n w h a t i s m e a n t b y t h e t e r m s p o n t a n e o u s a n d r a n d o m ,

i n t e r m s o f n u c l e a r p r o c e s s e s .

viii L e a r n t h e c h a r a c t e r i s t i c s a n d b e h a v i o u r o f α , β a n d γ

r a d i a t i o n .

S T R U C T U R E O F T H E ATO M

• The discovery of the electron by J.J Thompson• The discovery of the electron by J.J Thompsonprompted him in 1898 to suggest the plumpudding model for the atom.

• In this model, it was suggested that atomsconsist of positively charged lumps of matter,with negatively charged electrons embeddedin them.

Figure 4.1, page 120, Concepts of

Modern Physics, Beiser, 6th

edition, The McGrawHill

Companies, New York, 2003,


• In 1911, Hans Geiger and Ernest

�2�

• In 1911, Hans Geiger and ErnestMarsden, under the advise of ErnestRutherford, probed the atomic structureby performing the gold foil experiment.

• In this experiment, a stream of α (alpha)particles was shot at a thin gold foil. Thealpha particles are the nucleus of aHelium atom and have a charge ofmagnitude�2�.


• If Thompson’s model was correct, the• If Thompson’s model was correct, thedeflection of the alpha particles wereexpected to be less than 1°.

• However, what was observed was:

1. A large percentage of the α particlesdeviated at small angles (less than 1°).

2. A small fraction of the alpha particlesdeviated at large angles.

3. A tiny fraction were actually scatteredbackwards.


Source of image:

http://wiki.chemeddl.org/mediawiki/images/4/43/Chapter_4_page_17.jpg


• Rutherford proposed that there must be a• Rutherford proposed that there must be anucleus at the centre of the atom, where thepositive charges and mass are concentrated at.The rest of the atom is just empty space, withelectrons in it.

• Evidence:1. Majority of α particles pass through empty

space and get deviated at a very small angle.2. The α particles that pass through the atom

closer to the centre of the atom are eitherscattered at a large angle or scatteredbackwards.


Source of image:

http://wiki.chemeddl.org/mediawiki/images/7/7a/Chapter_4_page_18.jpg

S I M P L E M O D E L O F T H E

N U C L E A R ATO M

S I M P L E M O D E L O F T H E

N U C L E A R ATO M• The small concentrated positive charge at the• The small concentrated positive charge at the

centre of the atom is known as the nucleus,and the positive charges that inhibit thenucleus are known as protons.

• In addition to the protons, there are alsoneutral neutrons that occupy the nucleus.Collectively, the neutrons and protons areknown as nucleons (inhabitants of thenucleons).

• Negatively charged electrons orbit thenucleus.

PROTON NUMBER

• The proton number of an element gives• The proton number of an element givesthe number of protons in the nucleus ofan atom of the element.

• For example, the proton number of theelement carbon is 12. This means thatthere are 12 protons in the nucleus of acarbon atom.

• The proton number is denoted by the symbol Z.

NUCLEON NUMBER

• The nucleon number gives the total• The nucleon number gives the totalnumber of protons and neutrons in thenucleus of the element’s atom.

• For example, carbon has a nucleonnumber of 24. This means that thenucleus of the carbon atom has 12neutrons in addition to the 12 protons.

• The nucleon number is given the symbolA.

N U C L I D E R E P R E S E N TAT I O N

• Nuclides are a particular species of• Nuclides are a particular species ofan element with a specified numberof protons and neutrons.

• Nuclides are represented as �� ,

where is the element’s symbol,is the nucleon number, and is theproton number.

N U C L I D E R E P R E S E N TAT I O N

• Table 43.1, page

1441, Sear’s and

Zemansky’s

University

Physics, Young

and Freedman,

13th edition,

Pearson

Education, San

Francisco, 2012.

ISOTOPES

• The isotope of an element is the• The isotope of an element is thenucleus of that element that has thesame proton number but a differentnucleon number.

• This means that isotopes have thesame number of protons butdifferent number of neutrons.

ISOTOPES

• E.g.• E.g.

• The diagram shows the three isotopes ofoxygen. The proton number is thesubscript while the nucleon number issuperscript.

• Besides oxygen, other elements likecarbon and hydrogen also have differentisotopes.

E X A M P L E S

Oct/Nov 2009, Paper 11, question 40.

E X A M P L E S


E X A M P L E S

Oct/Nov 2010, Paper 22, question 7 (cont’d).

H O M E W O R K

1. May/June 2008, Paper 1, question 39.1. May/June 2008, Paper 1, question 39.

2. Oct/Nov 2008, Paper 1, question 38.


4. May/June 2009, Paper 1, question 36.





H O M E W O R K




NUCLEAR DECAY

• Nuclear decay occurs when the• Nuclear decay occurs when theunstable parent nuclei ofradioactive elements emitparticles and / or electromagneticradiation, leaving daughternuclei, which may be eitherstable or unstable.

NUCLEAR DECAY

• In the reaction ��

��

�


��

�

, the parent nuclide

uranium – 234 decays into thedaughter nuclide thorium – 230,giving off an α – particle (�

� )and gamma radiation.• The daughter nucleus will next

decay in series of steps toproduce a stable nuclide.

NUCLEAR DECAY

• In a nuclear reaction, such as nuclear• In a nuclear reaction, such as nucleardecay:

I. the proton number,

II. the nucleon number,

III. mass – energy, and

IV. momentum are

conserved.

NUCLEAR DECAY

• In the reaction �

�

��

��

• In the reaction �

�

��

�� , for example:

I. proton number before reaction =proton number after reaction = 9,

II. nucleon number before reaction =nucleon number after reaction =18.

NUCLEAR DECAY

• In the reaction �� → ��

��


�� → ��

��

, for example:I. proton number and nucleon number

is conserved, andII. an ��

� alpha (α) particle is emitted.III. gamma (γ) radiation, a form of EM

energy, is emitted. Some of thebinding energy in the parent nuclideis released.

NUCLEAR DECAY

• Binding energy is the energy that is• Binding energy is the energy that isstored in the nuclide to bind thenucleons together.• Evidence of binding energy: The mass of

the nucleus is more than the sum of themasses of all the nucleons. This effect isknown as the mass defect.• A certain amount of this mass defect is

converted into energy based on themass – energy equivalence principle.

NUCLEAR DECAY


��

��


��

��

, for example:

I. proton number and nucleonnumber is conserved, and

II. γ – radiation and a � particle(electron) are emitted.

NUCLEAR DECAY

• Nuclear decay process is classified as a• Nuclear decay process is classified as aspontaneous and random process.• It is spontaneous because its

occurrence is independent of anyexternal or environmental factors.• It is random because we cannot predict

which nucleus in a sample will decay.However, there is a constant probabilitythat the nucleus will decay in any fixedperiod of time.

E X A M P L E S

May/June 2008, Paper 1, question 40.

E X A M P L E S


H O M E W O R K

1. Oct/Nov 2008, Paper 2, question 8.1. Oct/Nov 2008, Paper 2, question 8.








H O M E W O R K

9. Oct/Nov 2010, Paper 11, question 40.9. Oct/Nov 2010, Paper 11, question 40.








H O M E W O R K





B E H AV I O U R O F R A D I AT I O N

• The three forms of radiation• The three forms of radiationassociated with nuclear decay are:I. α (alpha) radiation,II. β- (beta - minus) radiation, andIII. γ (gamma) radiation.

• We will look at the properties andbehaviour of these three radiationunder the influence of magnetic andelectric fields.


Source : http://webs.mn.catholic.edu.au/physics/emery/assets/the_co17.gif.


Source:

http://www.cyberphysics.co.uk/graphics/diagrams/radioactivity/electric_field_radiatio

n.gif.

E X A M P L E S


E X A M P L E S

May/June 2008, Paper 2, question 7 (cont’d).

H O M E W O R K

1. May/June 2009, Paper 21, question 8.1. May/June 2009, Paper 21, question 8.








Download - Chapter 27 Nuclear Physics

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