Ch32!1!3 Nuclear Physics Noor Arda
Transcript of Ch32!1!3 Nuclear Physics Noor Arda
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Chapter 32
Nuclear Physics and
Nuclear Radiation
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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"
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#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
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(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
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32' The Constituents and $tructure of
Nuclei
Nucleus contain positi%ely chared protons andneutral neutrons. Nucleus are characterized by the
number of protons and neutrons they contain.
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The notation for a particular nucleus of
element X is /ritten:
+0amples:
1asses and chares of atomic particles:
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The atomic mass unit u is defined so that the
mass of is e0actly 2 u.
This mass may also be /ritten in terms of
1ec2 usin E 5 mc2:
Careful measurements ha%e related the size ofthe nucleus to its atomic number:
*y contrast the radius of an atom is on the
order of 6'6 m. This means that the density of
the nucleus is e0tremely hih.
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7f the nucleus contains only positi%e chares /hy
doesn8t it fly apart due to their mutual repulsion9
There is another force actin called the stron
nuclear force /hich eeps it toether. 7ts
properties:• The stron force is short rane actin only to
distances of a couple fermis.
; The stron force is attracti%e and acts /ith nearlye<ual strenth bet/een protons and protons
protons and neutrons and neutrons and neutrons.
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$ince the stron
nuclear force is short
rane atoms /ithmore protons must
ha%e proportionally
more neutrons in order
to remain stable.
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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:
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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:
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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
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, 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
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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$31.5 &e'(
0.00061 u 0.57 &e'1 u
c E m c c
= ∆ = = ÷
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, amma ray is emitted /hen an e0cited
nucleus returns to its round state. Nuclei may
become e0cited throuh alpha or beta decay.
The asteris indicates the e0cited nucleus.
&ea%y nuclei decayin %ia alpha emission may
%ery /ell decay to a dauhter nucleus /hich is
also unstable and so on. The decays /ill
continue until a stable nucleus is reached.
?amma )ecay
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This is a diaram of the series of alpha and beta
decays in the decay chain.
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$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:
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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.
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)ifferent nuclei ha%e different decay constants λ.
, larer decay constant means the materialdecays a/ay more rapidly.
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$
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$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
$
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$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: