Chapter 21
The Nucleus:
A Chemist’s View
Chapter 21: The Nucleus: A Chemists View
21.1 Nuclear Stability and Radioactive Decay
21.2 The Kinetics of radioactive Decay
21.3 Nuclear Transformations
21.4 Detection and Uses of Radioactivity
21.5 Thermodynamic Stability
21.6 Nuclear Fission and Nuclear Fusion
21.7 Effects of Radiation
Subatomic particle tracks in a bubble charger
at CERN, the European particle physics
laboratory in Geneva, Switzerland.
Source: CERN, Geneva, Switzerland
Figure 21.1:
Known nuclides
DISTRIBUTION OF STABLE
NUCLIDES
• Protons Neutrons
•
•
•
•
Even
Even
Odd
Odd
Stable Nuclides
Even
Odd
Even
Odd
Total =
(like table 21.1 , P 980)
168
57
50
4
279
%
60.2
20.4
17.9
1.4
99.9%
PROPERTIES OF
FUNDAMENTAL PARTICLES
• Particle Symbol Charge
Mass
•
(x10 -19 Coulombs) (x10-27kg)
• Proton P
+1.60218
1.672623
• Neutron N
• Electron e
0
-1.60218
1.674929
0.0005486
NUCLEAR STABILITY
Modes of Radioactive Decay
•
•
•
•
•
•
•
•
Alpha Decay - Heavy Isotopes - 42He+2-
Beta Decay - Neutron Rich Isotopes - e - -
Positron Emission -Proton Rich Isotopes -
Electron Capture - Proton Rich Isotopes
x - rays
Gamma-ray emission(  - Decay of nuclear
excited states
Spontaneous Fission - Very Heavy Isotopes
Comparison of Chemical and Nuclear Reactions
Chemical Reactions
Nuclear Reactions
1. One substance is converted to
1. Atoms of one element typically
another,but atoms never change
change into atoms of another.
identity.
2. Orbital electrons are involved as 2. Protons, neutrons, and other
bonds break and form; nuclear
particles are involved; orbital
particles do not take part.
electrons take part.
3. Reactions are accompanied by
3.Reactions are accompanied by
relatively small changes in energy relatively large changes in
and no measurable changes in mass. energy and often measurable
changes in mass.
4. Reaction rates are influenced by
4. Reaction rates are affected by
temperature, concentration,
number of nuclei, but not by
catalysts, and the nature of the
temperature, catalysts, or the
chemical substance.
nature of the chemical substance.
Emission and Absorption of Light by Atoms
Light
Light
L
i
g
h
t
Nucleus of atom
Electron
Light Emission occurs when an
electron drops from a higher
energy level to a lower one.
Light Absorption by an
atom moves an electron
to a higher energy level.
Absorption and Emission of Light by The Nucleus
Excited state
Ground state
Protons and Neutrons in the nucleus are moved up to excited states
by the absorption of large amounts of energy, and they move from
excited states back to the ground states by the emission of large
amounts of energy! This energy is normally 106 times larger than
the energy emitted by electron transfers around atoms, and is in the
Gamma ray region of the electromagnetic spectrum.
Figure 12.1: Electromagnetic radiation has
oscillating electric (E) and magnetic (H) fields in
planes perpendicular
to each other and to the direction of propagation.
Figure 12.2: The nature of waves
Figure 12.3: Classification of
electromagnetic radiation
Figure 21.7: Schematic representation
of a Geiger-Muller counter
Alpha Decay -Heavy Elements
•
238U
+  + E
T1/ 2= 4.48 x 10 9 yrs
•
210Po
206Pb
234Th
++E
T 1/ 2= 138 days
•
256Rf
252No
++E
T1/ 2= 7 msec
•
241Am
237Np
T1/ 2= 433 days
++E
Beta Decay - Electron
Emission
P+ +  + Energy
• N
•
90Sr
90Y
+  + Energy
T1/ 2= 30 yrs
14N +  + Energy
• 14C
T1/ 2= 5730 yrs
247Am
247Cm +  + Energy
•
T1/ 2= 22 min
131Xe +  + Energy
• 131I
T1/ 2 = 8 days
Electron Capture - Positron Emission
P+ + e -
P+
51Cr
n + Energy = Electron Capture
n + e+ + Energy = Positron Emission
+ e-
51V
+ Energy
T1/2 = 28 days
7Be
7Li
+  + Energy
T1/2 = 53 days
177Pt
+ e-
177Ir
+ Energy
T1/2 = 11 sec
144Gd
144Eu
T1/2 = 4.5 min
+  + Energy
Gamma Ray Emission, the Nuclear Particles in the Nucleus dropping from excited
states to their ground states. Example is the decay of cobalt – 60 to excited states in
nickel – 60, which then decay to the ground state of 60Ni.
60Co
Beta decay, e-
2.405 Mev
1.173 Mev Gamma ray
1.332 Mev
1.332 Mev Gamma ray
Ground state of
60Ni
Natural Decay Series of Existing Isotopes
40K
40Ar
T1/2 = 1.29 x 109yrs
232 Th
208 Pb
T1/2 = 1.4 x 1010yrs
235U
207 Pb
T1/2 = 7 x 108yrs
238U
206
T1/2 = 4.5 x 109yrs
Pb
Figure 21.2:
Decay series
Natural Decay series for Uranium 238
238U
234 Th
234Pa
234U
230 Th
226Ra
222Rn
218Po
218At
214Pb
214Bi
214Po
=  decay
=  decay
238U
210 Tl
210Pb
210Bi
210
Po
-- 8  decays and 6  decays leaves you with --
206Hg
206Tl
206Pb
206Pb
Natural Decay series for Uranium 235
235U
231 Th
231Pa
227Ac
227 Th
223Fr
223Ra
219Ra
219At
215Po
215Bi
211Pb
=  decay
215At
211Bi
207 Tl
=  decay
211Po
235U
207Pb
-- 8  decays and 4  decays leaves you with -- 207Pb
Natural Decay series for Thorium 232
232
228Ra
Th
228Ac
228 Th
224Ra
220Rn
216Po
=  decay
212Pb
212Bi
208Tl
=  decay
212Po
232 Th
208Pb
-- 7  decays and 4  decays leaves you with -- 208Pb
Figure 21.3: The decay of a 10.0 -g
sample of strontium-90 over time.
Figure 21.4: change in the amount of
Molybdenum - 99 with time
Figure 21.5: Schematic diagram of a
cyclotron
Physicist works with a small cyclotron
at the University of California at
Berkeley.
Source: Corbis
CERN, the
world's largest
particle
accelerator,
lies at the foot
of the Jura
Mountains
near Geneva,
Switzerland.
Figure 21.6: Diagram of a linear accelerator
Accelerator
tunnel at
Fermilab, a highenergy particle
accelerator in
Batavia, Illinois.
Source: Fermilab Batavia, IL
Carbon-14
radioactivity is
often used to
date human
skeletons found
at
archaeological
sites
Source: University of
Pennsylvania Photo
Archives
Figure 21.8: Consumption of Na131I
Normal Thyroid
Source: Visuals Unlimited
An Enlarged Thyroid
Figure 21.9: Binding energy per nucleon
as a function of mass number.
Units used for Nuclear Energy Calculations
electron volt - (ev)
The energy an electron acquires when it moves through
a potential difference of one volt:
1 ev = 1.602 x 10-19J
Binding energies are commonly expressed in units
of megaelectron volts (Mev)
1 Mev = 106 ev = 1.602 x 10 -13J
A particularly useful factor converts a given mass defect
in atomic mass units to its energy equivalent in electron
volts:
1 amu = 931.5 x 106 ev = 931.5 Mev
Binding Energy per Nucleon of
Deuterium
Deuterium has a mass of 2.01410178 amu.
Hydrogen atom = 1 x 1.007825 amu = 1.007825 amu
Neutrons = 1 x 1.008665 amu = 1.008665 amu
2.016490 amu
Mass difference = Theoretical mass - actual mass
= 2.016490 amu - 2.01410178 amu = 0.002388 amu
Calculating the binding energy per nucleon:
Binding Energy
-0.002388 amu x 931.5 Mev / amu
=
Nucleon
2 nucleons
=
Calculation of the Binding Energy per
Nucleon for Iron- 56
The mass of Iron -56 is 55.934939 amu, it contains 26 protons and
30 Neutrons
Theoretical Mass of Fe - 56 :
Hydrogen atom mass = 26 x 1.007825 amu = 26.203450 amu
Neutron mass = 30 x 1.008665 amu = 30.259950 amu
56.463400 amu
Mass defect =Actual mass - Theoretical mass:
55.934939 amu - 56.46340 amu = - 0.528461 amu
Calculating the binding energy per nucleon:
Binding Energy = - 0.528461 amu x 931.5 Mev / amu
nucleon
56 nucleons
=
Calculation of the Binding Energy per
Nucleon for Uranium - 238
The actual mass of Uranium - 238 = 238.050785 amu, and it has
92 protons and 146 neutrons
Theoretical mass of Uranium 238:
Hydrogen atom mass = 92 x 1.007825 amu = 92.719900 amu
neutron mass = 146 x 1.008665 amu = 147.265090 amu
239.984990 amu
Mass defect = Actual mass - Theoretical mass:
238.050785 amu - 239.984990 amu = - 1.934205 amu
Calculating the Binding Energy per nucleon:
Binding Energy = -1.934205 amu x 931.5 Mev / amu
mucleon
238 nucleons
=
Mass and Energy in Nuclear Decay - I
Consider the alpha decay of 212Po
212Po
211.988842 g/mol
208Pb
T1/2 = 0.3 s
+  + Energy
207.976627 g/mol + 4.00151 g/mol
Products = 207.976627 + 4.00151 = 211.97814 g/mol
Mass = Po - Pb +  = 211.988842
211.97814
0.01070 g/mol
E = mC2 = (1.070 x 10-5 kg/mol)(3.00 x 108m/s)2
= 9.63 x 1011 J/mol
9.63 x 1011 J/mol
-12J/atom
=
1.60
x
10
6.022 x 1023 atoms/mol
Mass and Energy in Nuclear Decay - II
The Energy for the Decay of 212Po is 1.60 x 10-12J/atom
1.60 x 10-12J/atom
1.602 x 10-19 J/ev
1.00 x 107 evx
atom
= 1.00 x 107 ev/atom
1.0 x 10-6 Mev = __________________ !!!!!
ev
The decay energy of the alpha particle from 212Po is = 8.8 Mev !!!!
Figure 21.10: Both fission and fusion produce
more stable nuclides and are thus exothermic.
Figure 21.11: Upon capturing a neutron, the
235U nucleus undergoes fission to produce
two lighter nuclides, free neutrons (typically
three), and a large amount of energy.
Figure 21.12: Representation of a fission
process in which each event produces two
neutrons, which can go on to split other
nuclei, leading to a self-sustaining chain
reaction.
Figure 21.13: If the mass of the fissionable
material is too small, most of the neutrons escape
before causing another fission event; thus the
process dies out.
Figure 21.14: Nuclear power plant
Breeder reactor
at a nuclear
power plant in
St. Laurent-Des
Eaux, France.
Source: Stock Boston
A Uranium "button" for use as a fuel
in a nuclear reactor.
Figure 21.15: Schematic of a reactor core
Neutron Induced Fission Bombs and Reactors
There are three Isotopes with sufficiently long half-lives and a
significant fission cross-sections that are known to undergo
neutron induced fission, and are useful in fission reactors, and
Nuclear weapons. Of these only one exists on earth ( 235U which
exists at an abundance of 0.72% of natural Uranium)and that is the
isotope that we use in nuclear reactors for fuel and some weapons.
The three isotopes are:
233U
T1/2 = 1.59 x 105 years
sigma fission = 531 barns
235U
T1/2 = 7.04 x 108 years
sigma fission = 585 barns
239Pu
T1/2 = 2.44 x 105 years
sigma fission = 750 barns
Breeding Nuclear Fuel
There are two relatively common heavy Isotopes that will not undergo
neutron induced fission, that can be used to make other Isotopes that
do undergo neutron induced fission, and can be used as nuclear fuel in
a nuclear reactor.
Natural Thorium is 232 Th which is common in rocks.
232 Th
+ 10n
233 Th
233Pa
233 Th
+ Energy T1/2 = 22.3 min
233Pa +  + Energy
T1/2 = 27.0 days
233U +  + Energy
T1/2 = 1.59 x 105 yrs
Natural Uranium is 238U which is common in rocks as well.
238U
239U
239Np
+
1
0n
239U
+ Energy T1/2 = 23.5 min
239Np +  + Energy T
1/2 = 2.36 days
239Pu +  + Energy T
1/2 = 24400 years
A schematic
diagram of the
tentative plan
for deep
underground
isolation of
nuclear waste.
Disposal
system
Source: AP/Wide
World Photos
Figure 21.16: Plot of energy versus
the separation distance
Hydrogen Burning in Stars and
Nuclear Weapons
+  + 1.4 Mev
1H
+ 1H
2H
1H
+ 2H
3He
2H
+ 2H
3He
2H
+ 2H
3H
+ 1H + 4.0 mev
2H
+ 3H
4He
+ 1n + 17.6 Mev
2H
+ 3He
4He
+ 1H + 18.3 Mev
1H
+ 7Li
4He
+ 4He + 17.3 Mev
+ 5.5 Mev
+ 1n + 3.3 Mev
Easiest!
Highest
cross
section!
Helium Burning Reactions in Stars
12C
+ 4He
16O
16O
+ 4He
20Ne
20Ne
+ 4He
24Mg
28Si
32S
36Ar
+ 4He
+ 4He
24Mg
28Si
32S
+ 4He
36Ar
+4He
40Ca
Image of a
portion of the
Cyngus Loop
supernova
remnant taken
by the Hubble
space telescope.
Source: NASA
Positron Emission Tomography (PET) – A new and
Important Tool in Imaging Research
In the technique of positron Tomography, a positron emitting isotope
Is included into a molecule that is incorporated into a chemical reaction.
The positron emitted during the decay of the isotope will analite with an
Electron and emit two 511 kev gamma rays that can then be detected,
and the location of the decaying isotope isolated accurately.
B+ + e-
Two Gamma rays at 180o
Energy
511 kev
e-
+
B+
Common Positron emitting Isotopes:
11C,
511 kev
15O,
The two gamma
rays come away
at 180o.
T1/2 = 122s ; 18F, T1/2 = 1.83 hr
T1/2= 20.3 min , 13N, T1/2 = 9.97 min , ETC
Positron Emission Tomograph
The Tomograph is an
instrument that is a ring
of gamma ray detectors
that react very fast to
gamma rays, and by
measuring the time each
detector receives the signal
one can locate the point of
_ 1 cm in a
origin of the gamma ray to a precision of +
human being or any other physical object, without
any in vivo investigation. The detectors must have a
_ 250 ps per pulse.
capability of measuring up to +
Units of Radiation dose
rad = radiation - absorbed dose
the quantity of energy absorbed per kilogram of
tissue 1 rad = 1 x 10-2 J / kg
rem = roentgen equivalent for man, the unit of radiation
dose for a human:
1 rem = 1 rad x RBE
RBE = 10 for 
RBE = 1 for x-rays,  -rays, and ’s
Examples of Typical Radiation Doses
from Natural and Artificial Sources - I
Source of Radiation
Natural
Cosmic radiation
Radiation from the ground
From clay soil and rocks
In wooden houses
In brick houses
In light concrete houses
Radiation from the air (mainly radon)
Outdoors, average value
In wooden houses
In brick houses
In light concrete houses
Internal radiation from minerals in
tap water and daily intake of food
( 40K, 14C, Ra)
Average adult Exposure
30 -50 mrem/yr
~ 25 -170 mrem/yr
10 -20 mrem/yr
60 -70 mrem/yr
60 -160 mrem/yr
20 mrem/yr
70 mrem/yr
130 mrem/yr
260 mrem/yr
~ 40 mrem/yr
Examples of Typical Radiation Doses from
Natural and Artificial Sources - II
Source of Radiation
Artificial
Diagnostic x-ray methods
Lung (local)
Kidney (Local)
Dental (dose to the skin)
Therapeutic radiation treatment
Other sources
Jet flight (4 hrs)
Nuclear tests
Nuclear power industry
Total Average Value
Average Adult Exposure
0.04 - 0.2 rad/film
1.5 - 3.0 rad/film
< 1 rad/film
locally < 10,000 rad
~ 1 mrem
< 4 mrem/yr
< 1 mrem/yr
100 - 200 mrem/yr
Examples of Typical Radiation Doses from
Natural and Artificial Sources - III
From Kotz & Percell, Freshman Chemistry text
Smoke detectors
Smoking Tobacco(1.5 packs a day)
10 Airline flights
Airline Crew
1 millirem/year
9000
“
3
“
160
“
Hazards equivalent to the radiation dose of 10 mrem/year
3250 km travel by car
600 km travel by velocipede
150 km motorcycle
25 liters of wine
100 cigarettes smoked
1 diagonistic x-ray
Acute Effects of a Single Dose of Whole-Body Irradiation - I
Dose
(rem)
5 - 20
Effect
Lethal Dose
Population (%) No. of Days
Possible late effect; possible
--chromosomal aberrations
20 - 100 Temporary reduction in
--white blood cells
50+
Temporary sterility in men
--(100+ rem = 1 yr duration)
100-200 “Mild radiation sickness”:
vomiting, diarrhea, tiredness
in a few hours
Reduction in infection resistance
Possible bone growth retardation
in children
-------
Acute Effects of a Single Dose of
Whole-Body Irradiation - II
Dose
(rem)
Effect
Lethal Dose
Population (%) No. of Days
300+
Permanent sterility in Women
----
500
“Serious radiation sickness”:
marrow/intestine destruction
50 - 70
30
60 - 95
30
100
2
400 - 1000 Acute illness, early deaths
3000+
Acute illness, death in hours
to days
---