Chapter
22
Nuclear Chemistry
Brain images with 123I-labeled (γ-emitter) compound
Use of 131I (β-emitter) in detecting Hyper- or hypo- thyroidism
Chapter 22
Slide 2
Henri Becquerel March 1, 1896 :
Chapter 22
© 2003 John Wiley and Sons Publishers
Slide 3
Nuclear Reactions
01
Animation
Chapter 22
Slide 4
Alpha Decay:
Chapter 22
Slide 5
Beta Decay
 A beta particle
 Is an electron
emitted from the
nucleus.
 Forms when a
neutron in the
nucleus breaks
down.
1n
0e + 1P
0
-1
1
Chapter 22
Slide 6
Learning Check
Write the nuclear equation for the beta
decay of Co-60.
60Co
27
Chapter 22
Slide 7
Solution
Write the nuclear equation for the beta decay
of Co-60.
60Co
60Ni
27
28
+ 0e
1
beta particle
Chapter 22
Slide 8
Positron Emission:
Loss of a positron (a particle that has the same
mass as but opposite charge than an electron)
0
1
11
6
C
e
11

5
Chapter 22
B
+
0
1
e
Slide 9
Gamma  Radiation
•
•
Gamma radiation is energy emitted from an
unstable nucleus indicated by m.
In a nuclear equation for gamma emission,
the mass number and the atomic number are
the same.
99mTc
43
99Tc
43
+ 
Chapter 22
Slide 10
Electron Capture (K-Capture)
Addition of an electron to a proton in the nucleus
As a result, a proton is transformed into a neutron.
1
1
p
+
0
−1
e
1

0
Chapter 22
n
Slide 11
Nuclear Reactions
01
4
2
He
• Alpha () Radiation: Are helium nuclei, 2
that
contain two protons and two neutrons.
•
Alpha () emission reduces the mass number by 4
and the atomic number by 2.
Chapter 22
Slide 12
Balancing Nuclear Equations
1. Conserve mass number (A).
The sum of protons plus neutrons in the products must equal
the sum of protons plus neutrons in the reactants.
235
92 U
+ 10n
138
55 Cs
+
96
37 Rb
+ 2 10n
235 + 1 = 138 + 96 + 2x1
2. Conserve atomic number (Z) or nuclear charge.
The sum of nuclear charges in the products must equal the
sum of nuclear charges in the reactants.
235
92 U
+ 10n
138
55 Cs
+
96
37 Rb
+ 2 10n
92 + 0 = 55 + 37 + 2x0
Chapter 22
Slide 13
212Po
decays by alpha emission. Write the balanced
nuclear equation for the decay of 212Po.
4
alpha particle - 42He or 2
212Po
84
4He
2
+ AZX
212 = 4 + A
A = 208
84 = 2 + Z
Z = 82
212Po
84
1
1
p
+
4He
2
0
−1
e
+ 208
82Pb

Chapter 22
1
0
n
Slide 14
Chapter 22
Slide 15
Nuclear Reactions
•
06
Write balanced equations for:
1. Alpha emission from curium-242
2. Beta emission from magnesium-28
3. Positron emission from xenon-118
4. Electron capture by polonium-204
•
What particle is produced by decay of thorium-214
to radium-210?
Chapter 22
Slide 16
Radioactive Decay Rates
Chapter 22
01
Slide 17
Radioactive Decay Rates
•
01
Radioactive decay is kinetically a first-order process.
Decay Rate = k x N
N is number of radio active nuclei in the sample
The integrated form of the first-order rate law is:
[A]0
ln
[A]
=k t
Nt
ln
 kt
N0
Chapter 22
Slide 18
Amount of Radioactive Material
Remainig and half life
ln
[A]0
=k t
[A]
t½ = ln2
k
ln
[A]0
[A]
K = ln2
t1/2
= ln2 t
[A]0 = k1 . N0
t1/2
N0
ln
 ln 2(t / t 1/2 )
Nt
[A] = k1 . Nt
Nt
ln
  ln 2(t / t 1/2 )
N0
Chapter 22
Slide 19
Radioactive Decay Rates
Radioactive decay is a first-order process.
Radioactive Decay Rates
•
02
Half-Life: Radioactive
decay is characterized
by a half-life, t1/2, the
time required for the
number of radioactive
nuclei in a sample to
drop to half its initial
value.
ln 2
t1 
k
2
Chapter 22
Slide 21
Radioactive Decay Rates
Chapter 22
03
Slide 22
Chapter 22
Slide 23
Chapter 22
Slide 24
Chapter 22
Slide 25
How do you measure rate constant k ?
Nt
ln
 kt
N0
Chapter 22
Slide 26
Chapter 22
Slide 27
Chapter 22
Slide 28
Chapter 22
Slide 29
0.1813 /day
Chapter 22
Slide 30
Chapter 22
Slide 31
Chapter 22
Slide 32
Chapter 22
Slide 33
Chapter 22
Slide 34
Chapter 22
Slide 35
Chapter 22
Slide 36
Chapter 22
Slide 37
Chapter 22
Slide 38
Chapter 22
Slide 39
Chapter 22
Slide 40
Chapter 22
Slide 41
Chapter 22
Slide 42
Chapter 22
Slide 43
Carbon Dating
01
Carbon-14 is produced in the upper atmosphere by
the bombardment of nitrogen atoms with neutrons:

14
N + 1 n  14 C + 1 H
7
0
6
1
Radioactive 14CO2 is produced, which mixes with
ordinary 12CO2 and is taken up by plants during
photosynthesis.
Chapter 22
Slide 44
Radiocarbon Dating
14N
7
+ 01n
14C
6
14C
6
14N
7
+ 11H
+-10b
t½ = 5730 years
Uranium-238 Dating
238U
92
206Pb
82
+ 8 24 + 6-10b
Chapter 22
t½ = 4.51 x 109 years
Slide 45
Carbon Dating
02
• During an organism’s life, 14CO2 and 12CO2 are in a
dynamic equilibrium at a ratio of 1 part in 1012.
• When an organism dies, the 14C/12C ratio decreases
as 14C undergoes b decay to 14N.
• Measuring the 14C/12C ratio determines the age of
the sample with a high degree of certainty.
• Ages of 1000–20,000 years are commonly
determined. The half-life for 14C is 5730 years.
Chapter 22
Slide 46
Carbon Dating
04
• The carbon-14 decay rate of a sample obtained from
a young live tree is 0.260 disintegrations s–1 g–1. or
15.6 counts per minutes.
• Another sample prepared from an archaeological
excavation gives a decay rate of 0.186
disintegrations
Nt
ln
  ln 2(t / t 1/2 )
N0
s–1 g–1.
• What is the age of the object?
Chapter 22
Slide 47
Nuclear Stability
Neutron-Proton Ratios
•
•
•
Any element with more than one
proton (i.e., anything but
hydrogen) will have repulsions
between the protons in the
nucleus.
A strong nuclear force helps
keep the nucleus from flying
apart.
As the nuclei get heavier more
neutron is needed to provide a
stable nucleus.
Chapter 22
Slide 49
Neutron-Proton Ratios
•
•
Neutrons play a key role
stabilizing the nucleus.
Therefore, the ratio of neutrons
to protons is an important factor.
Chapter 22
Slide 50
Neutron-Proton Ratios
For smaller nuclei (Z 
20) stable nuclei have
a neutron-to-proton
ratio close to 1:1.
Chapter 22
Slide 51
Neutron-Proton Ratios
As nuclei get larger, it
takes a greater
number of neutrons to
stabilize the nucleus.
Chapter 22
Slide 52
Stable Nuclei
The shaded region in
the figure shows what
nuclides would be
stable, the so-called
belt of stability.
Chapter 22
Slide 53
Stable Nuclei
•
•
Nuclei above this belt have
too many neutrons.
They tend to decay by
emitting beta particles.
1n
0
0e
-1
+ 1P
1
Chapter 22
Slide 54
Stable Nuclei
Nuclei below the belt have
too many protons.
They tend to become more
stable by positron emission.
•
•
11
6
C
11
5

B
+
0
1
e
Alpha emission
212Po
84
4He
2
+ 208
82Pb
or electron capture:
1
1
p
+
0
−1
e

1
0
n
Chapter 22
Slide 55
Nuclear Stability
•
Radioactive products of
a radioactive decay will
undergo further
disintegration.
•
Some nuclei undergo a
whole series of
disintegrations called a
decay series, leading to
nonradioactive species.
Chapter 22
05
Slide 56
Binding energy
01
•
Since neutrons act as “glue” by overcoming
proton–proton repulsions, the strength of these
forces should be measurable.
•
However, the activation energy required to force
elementary particles close enough for reaction is
very high and requires temperatures of about 107 K.
•
Using Einstein’s equation ∆E = ∆mc2, we can
attempt to calculate energies.
Chapter 22
Slide 57
Binding energy
•
02
Consider the formation of a helium-4 nucleus:
Total theoretical mass of 2n + 2p
= 4.031 88 amu
Observed mass of helium-4 nucleus = 4.001 50 amu
Mass difference
•
= 0.030 38 amu
Mass difference is called the mass defect of the
nucleus. It results from combination of protons and
neutrons. It is converted to energy during reaction
and is a direct measure of nucleon binding energy.
Chapter 22
Slide 58
Energy Changes
•
Using the Einstein equation, we can calculate the binding energy for a
helium-4 nucleus:
•
The mass defect = 0.030 38 amu = 0.030 38 g/mol = 3.038 x 10–5
kg/mol.
•
∆E = ∆mc2 = (3.038 x 10–5 kg/mol) (3.00 X 108 m/s)2 (1J/(1
Kg.m2/s2)(1KJ/1000J)= 2.73 x 109 kJ/mol. (released energy)
(H2(g) + 1/2 O2 -> H2O (l),
•
03
ΔH = -2.858 x 10-2 kJ/mol)
The binding energy for helium-4 nucleus is 2.73 x 109 kJ/mol. Which
means that 2.73 x 109 kJ/mol is released when helium-4 nucleus
formed.
Mass loss of sun is 1010 Kg/sec, in 100 years it loses 6.6 PPT
Chapter 22
Slide 59
Energy Changes
04
•
Binding Energies are usually expressed on a per–
nucleon basis using the electron volt (eV) as the
energy unit.
•
1 eV = 1.60 x 10–19 J and 1 MeV = 1.60 x 10–13 J.
•
Helium-4 binding energy:
 2.73  1012 J/mol 
 1 nucleus 
1MeV




He  4 binding Energy 
 4 nucleons 
 6.022  1023 nuclei/mol 

13
J

 1.60  10
He  4 binding Energy  7.08 MeV/nucleo n
Chapter 22
Slide 60
Chapter 22
Slide 61
Chapter 22
Slide 62
Chapter 22
Slide 63
Chapter 22
Slide 64
Chapter 22
Slide 65
(
Chapter 22
1J/(1 Kg.m2/s2
)
Slide 66
(
Chapter 22
1J/(1 Kg.m2/s2
Slide 67
)
(See slide 60)
Helium-6 is radioactive
Chapter 22
Slide 68
Chapter 22
Slide 69
Chapter 22
Slide 70
Chapter 22
Slide 71
Chapter 22
Slide 72
Chapter 22
Slide 73
Nuclear Fission and Fusion
•
01
Nuclear Fission is the fragmentation of heavy
nuclei to form lighter, more stable ones.
Chapter 22
Slide 74
Nuclear Fission and Fusion
02
•
Nuclear Fission is the fragmentation of heavy
nuclei to form lighter, more stable ones.
•
Neutrons released in the fission of 235U can induce
three more fissions, then nine, and so on leading to
a chain reaction.
•
Critical mass is the mass required for the chain
reaction to become self-sustaining.
Chapter 22
Slide 75
Chapter 22
Slide 76
Chapter 22
Slide 77
Chapter 22
Slide 78
Chapter 22
Slide 79
Chapter 22
Slide 80
Chapter 22
Slide 81
Chapter 22
Slide 82
Nuclear Fusion
•
Fusion involves the combination of small nuclei
to form a larger nucleus.
Chapter 22
Slide 83
Nuclear Fusion
Nuclear Fusion
Among the processes thought to occur in the Sun:
1
1
1
1
2
1
H +
2
1
H+ H
3
2
He
3
2
He + He
4
2
3
2
4
2
1
1
3
2
H+ H
1
1
He + H
Chapter 22
0
1
e
1
1
He + 2 H
0
1
He + e
Slide 84
Nuclear Fusion
04
•
Nuclear Fusion is the formation of heavier nuclei
by the joining of lighter ones.
•
Fusion products are generally not radioactive.
•
Fusion requires high energies (temperatures over
107 K) to overcome the nuclear repulsions. The
highest temperature obtained in The Large Hadron
Collider LHC (CERN) is 4X1012
•
Fusion reactions are also called thermonuclear.
http://www.pppl.gov/projects/pages/tftr.html
Chapter 22
Slide 85
Chapter 22
Slide 86
Chapter 22
Slide 87
Nuclear Fission and Fusion
•
05
Nuclear Reactors “control” the fission of 235U and use the
energy
produced to
heat water
that drives
steam
turbines.
Chapter 22
Slide 88
Composition of the Spent Fuel
The spent nuclear fuel contains about 93%
uranium (mostly U-238)
• about 1% plutonium
• less than 1% minor actinides (neptunium,
americium, and curium)
• 5% fission products
•
Global Nuclear Wastes
•
Typical reactor will generate 20 to 30 tons of high-level
nuclear waste annually
•
The global volume of spent fuel is ,290,000 tons , and is
growing by approximately 10,000 tons annually.
•
Despite billion of dollars of investment in various disposal
options, the nuclear industry and governments have failed
to come up with a feasible and sustainable solution.
U-238 decay chain (main branch)
•
•
•
•
•
•
•
•
Uranium-238 (half-life: 4.46 billion years) alpha decay ==>
Thorium-234 (half-life: 24.1 days) beta decay ==>
Protactinium-234m half-life: 1.17 minutes) beta decay ==>
Uranium-234 (half-life: 245,000 years) alpha decay ==>
Thorium-230 (half-life: 75,400 years) alpha decay ==>
Radium-226 (half-life: 1,600 years) alpha decay
==>
Radon-222 (half-life: 3.82 days) ==> followed by radon
decay products (polonium, bismuth, lead isotopes)
Thorium-232
Thorium-232 is, like U-238, has its own decay
chain
• Dangerous decay products build up relatively
quickly in Th-232
• They are thorium-228, actinium-228 (a betaemitter), radium-228, and radium-224
• Radium-224 gives off radon-220 (which is similar to
radon-222)
•
Repository capacity
•
Three isotopes, which are linked through a decay
process (Pu241, Am241, and Np237), are the
major contributors to the estimated dose for
releases from the repository, typically occurring
between 100,000 and 1 million years, and also to
the long-term heat generation that limits the
amount of waste that can be placed in the
repository
Composition of the Spent Fuel
The spent nuclear fuel contains about 93%
uranium (mostly U-238)
• about 1% plutonium
• less than 1% minor actinides (neptunium,
americium, and curium)
• 5% fission products
•
Composition of the Spent Fuel
The spent nuclear fuel contains about 93%
uranium (mostly U-238)
• about 1% plutonium
• less than 1% minor actinides (neptunium,
americium, and curium)
• 5% fission products
•
Nuclear Fission & POWER
•
Currently* about 103
nuclear power plants
in the U.S. and about
442 worldwide. There
65 currently under
construction
•
17% of the world’s energy
comes from nuclear.
* 12-03-12
Chapter 22
Slide 96
Nuclear Fission and Fusion
© 2003 John Wiley and Sons Publishers
Courtesy US Department of Energy
Size of a fission bumb
Chapter 22
Slide 98
© 2003 John Wiley and Sons Publishers
The plutonium was produced in Hanford Nuclear reservation
Chapter 22
Slide 99
Nuclear Transmutation
•
Nuclear Transmutation
is the change of one
element into another.
•
Achieved by bombarding
atoms with high-energy
particles in a particle
accelerator.
•
Transmutation can
synthesize new elements.
Chapter 22
01
Slide 100
Nuclear Transmutation
02
•
Cyclotrons consist of D-shaped electrodes (dees)
with a large, circular magnet above and below the
vacuum chamber.
•
Particles are accelerated by making the dees
alternatively positive and negative.
•
When the particles are moving at sufficient velocity
they are allowed to escape the cyclotron and strike
the target.
Chapter 22
Slide 101
Nuclear Transmutation
Elements beyond 92 (transuranium) made
starting with an n, reaction
238 U
92
+
239 U
92
239 Np
93
1
239 U
92
+ 
--->
239 Np
93
+
0 b
-1
--->
239 Pu
94
+
0 b
-1
0n --->
Chapter 22
Slide 102
Nuclear Transmutation
Nuclear Transmutation: The change of one element
into another.
Plutonium-241 can be made by bombarding uranium-238
with alpha particles:
238
92
4
2
241
94
U + He
1
0
Pu + n
Plutonium-241 decays into americium-241:
241
94
241
95
Pu
Chapter 22
0
-1
Am + e
Slide 103
Nuclear Transmutation
Nuclear Transmutation: The change of one element
into another.
Cobalt-60 is used in radiation therapy for cancer patients.
The overall preparation process can be written as:
58
26
1
0
60
27
Fe + 2 n
Chapter 22
0
-1
Co + e
Slide 104
Radioisotopes in Medicine
•
1 out of every 3 hospital patients will undergo a nuclear
medicine procedure
•
24Na,
•
131I,
t½ = 14.8 hr, b emitter, thyroid gland activity
•
123I,
t½ = 13.3 hr, ray emitter, brain imaging
•
18F,
t½ = 1.8 hr, b emitter, positron emission tomography
•
99mTc,
t½ = 14.8 hr, b emitter, blood-flow tracer
t½ = 6 hr, ray emitter, imaging agent
Brain images
with 123I-labeled
compound
Chapter 22
Slide 105
Detecting Radioactivity
01
•
Matter is ionized by radiation.
•
We can detect radiation by measuring its ionizing
properties.
•
Ionizing radiation includes  particles, b particles, 
rays, X rays, and cosmic rays.
•
 ray & X rays are high-energy photons (l = 10–8 to
10–11 m). Cosmic rays originate in interstellar space.
Chapter 22
Slide 106
Detecting Radioactivity
02
•
A Geiger counter determines the amount of
ionization by detecting an electric current.
•
A thin window is penetrated by the radiation and
causes the ionization of Ar gas.
•
The ionized gas carried a charge and so current is
produced.
•
The current pulse generated when the radiation
enters is amplified and counted.
Chapter 22
Slide 107
Detecting Radioactivity
04
•
Scintillation counters use a substance called
phosphor (sodium iodide & thallium iodide), which
emits a flash of light when struck by radiation.
•
Flashes can be counted electronically and
converted to an electric signal.
Chapter 22
Slide 108
Application of Radioisotopes
05
•
Radiotracers (radio-labels) are used to follow an
element through a chemical reaction.
•
Photosynthesis has been studied using 14Ccontaining carbon dioxide:
14
614CO2 + 6H2O sunlight
C6H12O6 + 6O2
chlorophyll
•
The carbon dioxide is said to be 14C-labeled.
Chapter 22
Slide 109
Biological Effects of Radiation
01
•
The penetrating power of radiation is a function of
its mass: -rays > b-particles >> -particles.
•
When ionizing radiation passes through tissue it
removes an electron from water to form H2O+ ions.
•
The H2O+ ions react with another water molecule to
produce H3O+ and a highly reactive •OH radical.
•
Free radicals generally undergo chain reactions,
producing many radicals in the biomolecules.
Chapter 22
Slide 110
Biological Effects of Radiation
•
02
-rays are particularly harmful
because they penetrate in the
same way as X rays.
•
-particles interact with the
skin and b-particles interact
up to 1 cm into the tissue
•
-particles are particularly
dangerous when ingested or
inhaled.
Chapter 22
Slide 111
Radiation Measurement
•
•
•
The Curie measures the number of atoms that
decay in one second. Curie: 1 Ci = 3.7 x 1010
distintegrations/s
The rad* (radiation absorbed dose) measures the
radiation absorbed by the tissues of the body.
The rem (Roentgen equivalent for man (rem) )
measures the biological damage.
*1 Rad = 2.58 x 10-4 Coulombs /kg air. The exposure rate expresses the rate of charge production per unit mass of air and
is commonly expressed in roentgens per hour (R/h) or milliroentgens per hour (mR/h).
Chapter 22
Slide 112
Biological Effects of Radiation
Radiation absorbed dose (rad)
1 rad = 1 x 10-5 J/g of material
Roentgen equivalent for man (rem)
1 rem = 1 rad x Q
Quality Factor
-ray = 1
b=1
 = 20
Curie: 1 Ci = 3.7 x 1010
distintegrations/s
SI unit is the becquerel:
Bq = 1 distintegrations/s
Chapter 22
Slide 113
Units of Radiation Measurement
Chapter 22
Slide 114
Background Radiation
•
A person is exposed to
radiation from naturally
occurring radioisotopes
and medical X rays.
Chapter 22
Slide 115
Biological Effects of Radiation
Chapter 22
08
Slide 116
Biological Effects of Radiation
Chapter 22
07
Slide 117
Biological Effects of Radiation
Chapter 22
Slide 118
Applications of Nuclear Chemistry
Dating with Radioisotopes
The half-life of carbon-14 is 5730 years:
14
14
0
14
7
-1
C
N + e
The measured ratio of carbon-14/carbon-12 after
death can determine how long ago the organism died.
Chapter 22
Slide 119
Applications of Nuclear Chemistry
Dating with Radioisotopes
Geologic age can be determined by analysis of
potassium-40:
40
19
0
-1
40
18
40
19
40
18
K + e
K
Ar
0
1
Ar + e
Potassium-40 has a half life of 1.25 billion years. Mass Spectroscopy
is used to measure Ar-40 in a sample of molten rock to calculate the
age of the rock.
Chapter 22
Slide 120
Bone scan Using Radiactive Technetiun-99
Bone scan