ch32!1!3 nuclear physics noor arda

8/18/2019 Ch32!1!3 Nuclear Physics Noor Arda

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Copyright © 2010 Pearson Education, Inc.

Chapter 32

Nuclear Physics and

Nuclear Radiation




For Chapter 32:Please emphasize on 32.2 and 32.4:

The students should be able to

determine the mass number and atomic number for parent

and dauhter nuclei in alpha and beta decay and amma

radiation. !32.2"

explain the terms binding energy and binding energy per nucleon

!32.4"




#nits of Chapter 32

• The Constituents and $tructure of Nuclei

• Radioacti%ity

• &alf'(ife and Radioacti%e )atin

• Nuclear *indin +nery

• Nuclear Fission

• Nuclear Fusion

• Practical ,pplications of Nuclear Physics




(esson -utcome

At the end of the class, student should beable to

• Define Proton, Neutron, Nucleons, atomicNumber, mass number and atomic mass unit

• Explain properties of alpha, beta and gammaradiation.

• Define Radioactivity• Explain Alpha Decay, eta Decay and !amma

Decay




32' The Constituents and $tructure of

Nuclei

Nucleus contain positi%ely chared protons andneutral neutrons. Nucleus are characterized by the

number of protons and neutrons they contain.




The notation for a particular nucleus of

element X is /ritten:

+0amples:

1asses and chares of atomic particles:


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The atomic mass unit u is defined so that the

mass of is e0actly 2 u.

This mass may also be /ritten in terms of

1ec2 usin E 5 mc2:

Careful measurements ha%e related the size ofthe nucleus to its atomic number:

*y contrast the radius of an atom is on the

order of 6'6 m. This means that the density of

the nucleus is e0tremely hih.



7f the nucleus contains only positi%e chares /hy

doesn8t it fly apart due to their mutual repulsion9

There is another force actin called the stron

nuclear force /hich eeps it toether. 7ts

properties:• The stron force is short rane actin only to

distances of a couple fermis.

; The stron force is attracti%e and acts /ith nearlye<ual strenth bet/een protons and protons

protons and neutrons and neutrons and neutrons.



$ince the stron

nuclear force is short

rane atoms /ithmore protons must

ha%e proportionally

more neutrons in order

to remain stable.



32'2 Radioacti%ity

. ,lpha particles /hich consist of t/o neutronsand t/o protons.

2. +lectrons and positrons also called =for

historical reasons> beta rays. Positrons ha%e

the same mass as electrons but are positi%ely

chared.

3. ?amma rays /hich are hih'enery photons.

#nstable nucleus can either decay into a stable

nucleus or can return to the round state.

arious emissions that result are no/n as

radioacti%ity:



α rays can barely penetrate a sheet of paper.

• β rays =both β' and β@> can penetrate a fe/

millimeters of aluminum.

• γ rays can penetrate se%eral centimeters of

lead.

Penetratin abilities:



Ahen a nucleus decays by emittin an alpha

particle it loses t/o protons and t/o neutrons

$ymbolically:

&ere X is the parent nucleus

and Y is the dauhter.

,lpha )ecay



, nucleus that decays %ia beta decay emits

an electron and positron.

There is a third particle emitted /hich has noelectric chare and little called the neutrino.

*eta )ecay



The follo/in nuclei are obser%ed to decay by

emittin a B' particle. Arite out the decay

process for each of these nuclei and determinethe enery released in each reaction.

35 35 –

16 17 C! e υ → + +

i

"

3#.$6$033 u

3#.$6%%53 u

3#.$6%%53 u 3#.$6$033 u 0.0001%0 u

m

m

m

=

=

∆ = − = −

22 2$31.5 &e'(

0.0001%0 u 0.16% &e'1 u

c E m c c

= ∆ = = ÷

212 212 –

%2 %3P) *i e υ → + +

i

"

211.$$1%% u

211.$$1272 u

211.$$1272 u 211.$$1%% u 0.00061 u

m

m

m

=

=

∆ = − = −

22 2$31.5 &e'(

0.00061 u 0.57 &e'1 u

c E m c c

= ∆ = = ÷



, amma ray is emitted /hen an e0cited

nucleus returns to its round state. Nuclei may

become e0cited throuh alpha or beta decay.

The asteris indicates the e0cited nucleus.

&ea%y nuclei decayin %ia alpha emission may

%ery /ell decay to a dauhter nucleus /hich is

also unstable and so on. The decays /ill

continue until a stable nucleus is reached.

?amma )ecay



This is a diaram of the series of alpha and beta

decays in the decay chain.



$ome nuclei decay more rapidly than others. The

rate of decay the number of decays per second

is called the acti%ity.

The curie =and the millicurie and microcurie>

are most commonly used.

T/o units of acti%ity:



32'3 &alf'(ife and Radioacti%e )atin

Nuclear decay is a random process in that /e

do not no/ /hich nucleus /ill decay at /hat

time. &o/e%er if /e ha%e a lare number ofsimilar nuclei /e can predict the rate at /hich

they decay <uite /ell.

The number that decay /ithin a i%en timeinter%al is al/ays the same fraction of the total

number at the beinnin of the inter%alD this is

e0ponential decay.



)ifferent nuclei ha%e different decay constants λ.

, larer decay constant means the materialdecays a/ay more rapidly.



$




$ummary

• 1ass of is e0actly 2 u.

•

• Nuclear radius:

• Nuclear density is appro0imately constant

• $tron nuclear force holds nuclei toether

• Radioacti%ity is the emission from the decay of

an unstable or e0cited nucleus

$



$ummary

• ,n alpha particle =helium nucleus> is t/o

protons and t/o neutrons.

• ,lpha decay:

• *eta decay:

• ?amma decay occurs /hen an e0cited nucleus

decays to its round state.

• ,cti%ity is the number of decays per second:

ch32!1!3 nuclear physics noor arda

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