The Nucleus:

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Chapter 21

• The Nucleus
• A Chemists View

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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
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Subatomic particle tracks in a bubble charger at
CERN, the European particle physics laboratory in
Geneva, Switzerland.
Source CERN, Geneva, Switzerland
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Figure 21.1 Known nuclides
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DISTRIBUTION OF STABLE NUCLIDES

• Protons Neutrons Stable Nuclides
• Even Even 168
  60.2
• Even Odd 57
  20.4
• Odd Even 50
  17.9
• Odd Odd 4
  1.4

279
99.9
Total
(like table 21.1 , P 980)
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PROPERTIES OF FUNDAMENTAL PARTICLES

• Particle Symbol Charge Mass
• (x10 -19 Coulombs)
  (x10-27kg)
• Proton P 1.60218
  1.672623
• Neutron N 0
  1.674929
• Electron e -1.60218 0.0005486

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NUCLEAR STABILITYModes of Radioactive Decay

• Alpha Decay - Heavy Isotopes - 42He2-?
• 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

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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.
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Emission and Absorption of Light by Atoms
Light
Light
Light
Nucleus of atom
Electron
Light Absorption by an atom moves an electron
to a higher energy level.
Light Emission occurs when an electron drops
from a higher energy level to a lower one.
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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.
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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.
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Figure 12.2 The nature of waves
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Figure 12.3 Classification of electromagnetic
radiation
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Figure 21.7 Schematic representation of a
Geiger-Muller counter
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Alpha Decay -Heavy Elements

• 238U 234Th ?? E
• T1/ 2 4.48 x 10 9 yrs
• 210Po 206Pb ? E
• T 1/ 2 138 days
• 256Rf 252No ? E
• T1/ 2 7 msec
• 241Am 237Np ? E
• T1/ 2 433 days

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Beta Decay - Electron Emission

• N P ?? Energy
• 90Sr
  90Y ?? Energy
• T1/ 2 30 yrs
• 14C 14N ?? Energy
• T1/ 2 5730 yrs
• 247Am
  247Cm ?? Energy
• T1/ 2 22 min
• 131I 131Xe ?? Energy
• T1/ 2 8 days

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Electron Capture - Positron Emission
P e - n Energy
Electron Capture
P n e Energy
Positron Emission
51Cr e - 51V
Energy T1/2 28 days
7Be 7Li ??
Energy T1/2 53 days
177Pt e -
177Ir Energy T1/2 11 sec
144Gd 144Eu ??
Energy T1/2 4.5 min
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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.
Beta decay, e-
60Co
2.405 Mev
1.173 Mev Gamma ray
1.332 Mev
1.332 Mev Gamma ray
Ground state of 60Ni
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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 Pb T1/2 4.5
x 109yrs
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Figure 21.2 Decay series
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Natural Decay series for Uranium 238
238U 234 Th
234Pa 234U 230 Th 226Ra
222Rn 218Po 214Pb


218At 214Bi 210
Tl
214Po 210Pb
206Hg ? decay
210Bi
206Tl ??? decay
210 Po 206Pb
238U -- 8 ?? decays and 6 ? decays leaves you
with -- 206Pb
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Natural Decay series for Uranium 235
235U 231 Th 231Pa
227Ac 223Fr 219At
215Bi 227 Th 223Ra
219Ra 215Po 211Pb

215At 211Bi
207 Tl
211Po
207Pb
?? decay ?? decay
235U -- 8 ? decays and 4 ??? decays leaves you
with -- 207Pb
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Natural Decay series for Thorium 232
232 Th 228Ra 228Ac 228
Th 224Ra 220Rn
216Po 212Pb

212Bi 208Tl

212Po 208Pb
?? decay ?? decay
232 Th -- 7 ?? decays and 4 ??? decays leaves
you with -- 208Pb
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Figure 21.3 The decay of a 10.0 -g sample of
strontium-90 over time.
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Figure 21.4 change in the amount of Molybdenum
- 99 with time
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Figure 21.5 Schematic diagram of a cyclotron
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Physicist works with a small cyclotron at the
University of California at Berkeley.
Source Corbis
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CERN, the world's largest particle accelerator,
lies at the foot of the Jura Mountains near
Geneva, Switzerland.
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Figure 21.6 Diagram of a linear accelerator
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Accelerator tunnel at Fermilab, a high-energy
particle accelerator in Batavia, Illinois.
Source Fermilab Batavia, IL
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Carbon-14 radioactivity is often used to date
human skeletons found at archaeological sites
Source University of Pennsylvania Photo Archives
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Figure 21.8 Consumption of Na131I
Normal Thyroid An
Enlarged Thyroid
Source Visuals Unlimited
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Figure 21.9 Binding energy per nucleon as a
function of mass number.
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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
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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
Mev /
nucleon

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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 - 56.463400 amu -
0.528461 amu
Calculating the binding energy per nucleon
Binding Energy - 0.528461 amu x 931.5
Mev / amu nucleon
56 nucleons

Mev / nucleon
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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

239.98499 amu
Mass defect Actual mass - Theoretical mass
238.050785 amu - 239.98499 amu - 1.934205 amu
Calculating the Binding Energy per nucleon
Binding Energy -1.934205 amu x 931.5 Mev /
amu mucleon
238 nucleons

Mev / nucleon
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Mass and Energy in Nuclear Decay - I
Consider the alpha decay of 212Po T1/2
0.3 ?s
212Po 208Pb ?
Energy
211.988842 g/mol 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 6.022 x 1023 atoms/mol
____________________ J/atom
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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 ev/atom
10.0 x 106 ev 1.0 x 10-6 Mev atom
ev
x
10.0 Mev/atom !!!!!
The decay energy of the alpha particle from 212Po
is 8.8 Mev !!!!
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Figure 21.10 Both fission and fusion produce
more stable nuclides and are thus exothermic.
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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.
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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.
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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.
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Figure 21.14 Nuclear power plant
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Breeder reactor at a nuclear power plant in St.
Laurent-Des Eaux, France.
Source Stock Boston
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A Uranium "button" for use as a fuel in a
nuclear reactor.
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Figure 21.15 Schematic of a reactor core
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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
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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
Energy T1/2 22.3 min 233 Th
233Pa ?? Energy T1/2 27.0 days
233Pa 233U ?? Energy
T1/2 1.59 x 105 yrs Natural Uranium is 238U
which is common in rocks as well. 238U
10n 239U Energy T1/2 23.5
min 239U 239Np ?? Energy
T1/2 2.36 days 239Np 239Pu ??
Energy T1/2 24400 years
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A schematic diagram of the tentative plan for
deep underground isolation of nuclear waste.
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Disposal system
Source AP/Wide World Photos
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Figure 21.16 Plot of energy versus the
separation distance
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Hydrogen Burning in Stars and Nuclear
Weapons
1H 1H 2H ?? 1.4
Mev 1H 2H 3He
5.5 Mev 2H 2H 3He
1n 3.3 Mev 2H 2H
3H 1H 4.0 mev 2H 3H
4He 1n 17.6 Mev
Easiest!

Highest 2H 3He 4He
1H 18.3 Mev cross

section! 1H 7Li
4He 4He 17.3 Mev
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Helium Burning Reactions in Stars
12C 4He 16O 16O
4He 20Ne 20Ne 4He
24Mg 24Mg 4He
28Si 28Si 4He
32S 32S 4He
36Ar 36Ar 4He
40Ca
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Image of a portion of the Cyngus Loop supernova
remnant taken by the Hubble space telescope.
Source NASA
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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-
Energy Two Gamma rays at 180o
511 kev
The two gamma rays come away at 180o.
511 kev
e- B
Common Positron emitting Isotopes 15O, T1/2
122s 18F, T1/2 1.83 hr 11C, T1/2 20.3
min , 13N, T1/2 9.97 min , ETC
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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 origin of the gamma ray to a
precision of 1 cm in a human being or any other
physical object, with out any in vivo
investigation. The detectors must have
a capability of measuring up to 250 ps per
pulse.
_
_
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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
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Examples of Typical Radiation Doses
from Natural and Artificial Sources - I
Source of Radiation
Average adult Exposure
Natural
Cosmic radiation
30 -50 mrem/yr Radiation from the
ground From clay soil and rocks
25 -170 mrem/yr In wooden
houses
10 -20 mrem/yr In brick houses
60 -70 mrem/yr
In light concrete houses
60 -160 mrem/yr Radiation from the air
(mainly radon) Outdoors, average value
20 mrem/yr In wooden
houses
70 mrem/yr In brick houses
130 mrem/yr In light
concrete houses
260 mrem/yr Internal radiation from minerals in
tap water and daily intake of food
40 mrem/yr ( 40K, 14C, Ra)
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Examples of Typical Radiation Doses
from Natural and Artificial
Sources - II
Source of Radiation
Average Adult Exposure
Artificial
Diagnostic x-ray methods
Lung (local)
0.04 - 0.2 rad/film
Kidney (Local)
1.5 - 3.0 rad/film Dental (dose
to the skin) lt 1
rad/film Therapeutic radiation treatment
locally lt 10,000 rad Other sources
Jet flight (4 hrs)
1 mrem Nuclear tests
lt
4 mrem/yr Nuclear power industry
lt 1 mrem/yr Total Average
Value
100 - 200 mrem/yr
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Examples of Typical Radiation
Doses from Natural and
Artificial Sources - III
From Kotz Percell, Freshman Chemistry text
Smoke detectors
1 millirem/year Smoking
Tobacco(1.5 packs a day) 9000
10 Airline flights
3 Airline Crew
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
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Acute Effects of a Single Dose of Whole-Body
Irradiation - I
Dose
Lethal Dose (rem)
Effect Population
() No. of Days
5 - 20 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
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Acute Effects of a Single Dose
of Whole-Body Irradiation -
II
Dose
Lethal Dose (rem)
Effect
Population () No. of Days
300 Permanent sterility in Women
---- --- 500
Serious radiation sickness 50 - 70
30
marrow/intestine destruction 400 - 1000 Acute
illness, early deaths 60 - 95
30 3000 Acute illness, death
in hours 100 2
to days