Lecture 64 Nuclear Chemistry III

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Lecture 64 Nuclear Chemistry - III
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Nuclear Fission
92Kr
36
n
unstable 236U
235U
3 1n
0
141Ba
56
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Nuclear Fission

• 1n 235U 141Ba 92Kr 3 1n
• Many other fission pathways exist
• 1n 235U 137Te 97Zr 2 1n

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Nuclear Fission
Fission Yield
70
Mass Number (A)
170
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Nuclear Fission

• Result fission waste contains MANY radionuclides
  which decay
• 90Sr t1/2 28.1 y substitutes for Ca in bones
• 131I t1/2 8.1 d concentrates in thyroid
• 129I t1/2 1.7 x 107 y

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Nuclear Fission
n
235U
235U
235U
235U
235U
235U
235U
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Nuclear Fission
large mass of 235U
small mass of 235U
many neutrons escape, reaction dies
(subcritical)
few neutrons escape, reaction is
self-sustaining (supercritical)
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Nuclear Fission

• subcritical no reaction
• just critical controlled release of power
• supercritical a bomb

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Nuclear Fusion

• Energy of the Sun

protium
deuterium
1
2
3
H H He
1
1
2
3
1
0
4
He H He e
2
1
1
2
All are very exothermic!
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Nuclear Fusion
electrostatic repulsion
d
E
1H 1H
d
nuclear force
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Detecting and Measuring Radioactivity
a, b, g, X-rays, cosmic rays (protons)

molecule or atom
ion e-
Ionizing Radiation
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Detection systems
Window
Geiger Counter
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Detection systems
-
Window

Geiger Counter
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Detection systems
Ar/CH4(g)
-
Window

e-
Ar
to power supply, counter
Geiger Counter
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Detection systems
NaI(Tl)(s)
g
TI TI
TI TI hn
photo- detector
Scintillation counter
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Quantifying Radiation

• 1 Becquerel (Bq) 1 disintegration / s
• 1 Curie (Ci) 3.7 x 1010 disintegrations / s
• ( disintegration rate of 1 g 226Ra)

leave a few lines here!
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for example,

• A sample contains 10-12 g 131I. How many Ci of
  radiation does the sample produce? (t1/2 8.07
  d)
• rate kN
• k 0.693/t1/2 0.0859 d-1
• N (10-12 g / (131 g/mol)) x NAV
• 4.6 x 109 (atoms of 131I)

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for example,

• rate kN
• (0.0859 d-1)(4.6 x 109)
• 3.95 x 108 d-1
• 4570 s-1
• 4750 Bq
• thus, rate 4570 s-1/(3.7 x 1010 s-1 Ci-1)
• 1.24 x 10-7 Ci 0.12 mCi

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Quantifying Radiation

• 1 Becquerel (Bq) 1 disintegration / s
• 1 Curie (Ci) 3.7 x 1010 disintegrations / s
• ( disintegration rate of 1 g 226Ra)
• 1 rad 0.01 J/kg tissue (energy absorbed)
• 1 rem 0.01 J/kg tissue (damage done)

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In terms of damage done,

• 1 rad a gt 1 rad b gt 1 rad g
• but
• 1 rem a 1 rem b 1 rem g

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Short Term Radiation Exposure

• lt 25 rem no problemos
• 25-50 rem temporary loss of white blood
  cells
• 100-200 rem loss of most white blood cells
• gt500 rem say your prayers

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Typical Doses for You (rem)

• A. Natural Sources
• Cosmic radiation 0.050
• From the Earth 0.047
• From building materials 0.003
• In your tissues 0.021
• From inhalation of air 0.005
• TOTAL 0.126

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Typical Doses for You (rem)

• B. Anthropogenic Sources
• Medical X-rays 0.050
• Radiotherapy 0.010
• Nuclear power industry 0.0002
• TV tubes 0.002
• Radioactive fallout 0.004
• TOTAL 0.066
• Grand Total 0.192