Chapter 1 Structure of matter Chapter 2 Nuclear transformation.
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Transcript of Chapter 1 Structure of matter Chapter 2 Nuclear transformation.
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Chapter 1 Structure of matterChapter 2 Nuclear transformation
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The nucleus
isotope same Nproton, different Nneutron
isotone same Nneutron, different Nproton
isobar same (Nneutron+ Nproton), different Nproton
isomer same Nproton, same Nproton,
different nuclear energy state
XAZ
A the mass number (Nproton+ Nneutron)Z the atomic number (Nproton )
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Charts of isotopes
Z=N
Isotope
Isobar
Isotone
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Atomic mass and energy units
1 amu = mass of =1.6610-27 kg 1 eV =1 V1.602 10-19 C =1.602 10-19 JEinstein’s principle of equivalence of mass and energy
C12612
1
MeV0.511
m/sec103kg109.12831
2
2
cm
mcE
e
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Decay constant ()
Nt
NN
t
N
or
teN
N
tNN
NC
Nt
CtN
dtN
dN
0
0
0
0
lnln
ln
ispresentnumberthe,0If
ln
teNN 0
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Activity
1 Ci =3.71010 disintegrations/sec =3.71010 dps =3.71010 Bq
teAA
Nt
NA
0
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The half-life (T1/2) & the mean life (T)
The half-life (T1/2) The mean life (T)
2/1
0
2ln2
12
1
2/1
T
e
NN
T
693.02ln
2/1 T
00 NNT
2/12/1 44.1
693.0
1T
TT
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Radioactive equilibrium
22112
011
NNdt
dN
eNN t
teN
N )12(
12
0112 1
)(
teA
A )12(
12
112 1
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Transient equilibrium
T1>T2 (1<2)
Transient equilibrium
time
activ
ity
112
22 AA
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Secular equilibrium
T1>>T2 (1<<2)
A2 = A1
Secular equilibrium
time
activ
ity
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particle decay
Q = the disintegration energy
= the difference in mass between the parent nucleus and product nuclei
E 510 MeV (discrete energy)
QHeYX 42
4A2Z
AZ
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Negatron(-) emission
An excessive number of neutrons or a high neutron-to-proton (n/p) ratio
anti-neutrino Q = the difference in mass between and the
sum of the masses of and the particles emitted.
QνYX AZ
AZ
~011 β
~
XAZ
YAZ 1
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Positron(+) emission
A deficit of neutrons or a low n/p ratio
neutrinoAnnihilation
QνYX AZ
AZ β011
ν
+positron
free electron
0.511 MeV photon
0.511 MeV photon
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The -ray spectrum
The average energy of the particles is approximately Emax/3.
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Electron capture
The unstable nuclei with neutron deficiency may increase their n/p ratio by EC.
An alternative process to the positron decayK capture characteristic x-rays
(L or M capture) Auger electrons
ν nep 10
01
11
QνYeX AZ
AZ 1
01
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K
LM
hole
Characteristic radiation
An empty hole in a shell is filled by electron from outer shell with an emission of characteristic radiation.discrete energy
h=EK - EL
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K
LM
hole
Auger Electrons
The absorption of characteristic x-rays by orbital electrons and reemission of the energy in the form of monoenergetic electronsdiscrete energy
E=h-EM=EK – EL-EM
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Nuclear reactions (1)
The , p reaction– – Threshold energy– AX (, p) A+3Y
The , n reactionProton bombardmentDeuteron bombardment
QYX AZ
AZ
HHe 11
42
31
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Nuclear reactions (2)
Neutron bombardment– Neutron, no electric charge effective in penetrating the nuclei and producing nuclear reactions– – n, reaction
Photon disintegrationFission– Chain reaction
Fusion
HeLinB 42
73
10
105
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Activation of nuclides
The yield of a nuclear reaction– The number of bombarding particles– The number of target nuclei– The probability of the occurrence
• Cross-section– 1 barn = 10-24 cm2
The growth of activity– Saturation activity
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Thank you for your attention!