Physical Science
Nuclear Physics
Slides subject to change
Atoms

Each chemical element is composed of
tiny, indivisible particles called atoms,
which are identical for that element but
different (masses and chemical properties)
from atoms of other elements.

Consists of negatively
charged electrons and a
small positively charged
nucleus.
Planetary Model
Nucleus



Nucleus consists of positively charged
protons and, electrically neutral neutrons.
Protons and neutrons are collectively called
nucleons.
Relative size - a marble in a football
stadium.
Atom
diameter
Nucleus
diameter
1x10-10 m
1x10-14 m
Labels
Each element is assigned a chemical
symbol. This symbol usually originates
from its name or its Latin name.
 H = Hydrogen
 He = Helium
 C = Carbon
 Number of protons Z is the atomic
number. All the atoms of an element have
the same atomic number.

Mass Number
Number of protons is the atomic
number, Z.
 Number of protons plus neutrons
is the mass number, A.

Mass
Number
A
Z
X
Atomic Number, or
number of protons
In General
238
Element
92
U
Uranium
Details on a Uranium Nucleus
How many protons? 92
 How many neutrons? 238 – 92 = 146
 Mass number? 238

238
92
U
Uranium
Background on Uranium
Discovered in 1789, named after planet
Uranus discovered 8 years earlier.
 Common element in Earth’s crust. One of
the radioactive elements responsible for
molten layer between Earth’s crust and
core (more uranium in Earth’s crust than
silver).
 First radioactive material discovered in
1896.

Isotopes
Forms of an element with different
numbers of neutrons.
 Have same chemical properties, may have
different physical properties.

238
92
U
Uranium 238
plentiful in
nature, 99.3%
235
92
U
Uranium 235 rare in
nature but needed for
power/weapons, 0.7%
Strong Nuclear Force
Overcomes Coulomb
repulsion force.
 Short range, only nearest
neighbor nucleons involved.
 Large nucleus becomes
very unstable.
 When over 83 protons,
nucleus is subject to
spontaneous disintegration.

Nucleus of U-235:
protons in red,
neutrons in grey.
Radioactivity

Some nuclei spontaneously
decay.
Discovered in 1896 by Henri Becquerel
studying fluorescence and
phosphorescence, and working with
uranium salts and photographic plates.
 The spontaneous process of nuclei
undergoing a change by emitting particles
or rays is called radioactive decay.

An Alpha Decay Process
Alpha particles: He nuclei (2 protons, 2
neutrons)
 Mass numbers and atomic numbers add
up and match. Uranium decays to thorium.

+
238
92
U
234
90
4
Th + He
2
+
Beta Decay
Beta particles: Electrons. A neutron decays
in the nucleus to a proton and a neutron.
 Atomic mass and atomic numbers add up
and match.
 Example is Cobalt-60. Decays to an
unstable nickel atom.

60
27
60
0
28
-1
Co Ni* + e
Gamma Decay
Gamma rays consist of high energy photons
with energies above about 100,000 eV
(>1019 Hz).
 Due high energy content, gamma rays can
cause serious damage when absorbed by
living cells (photons strike DNA).

60
27
Ni* Ni + γ
60
27
Uranium
Pitchblende ore
contains uranium
Lisbon Valley, UT
Commercial
Uranium :
“Yellow Cake”
Radium
Discovered by Pierre and
Marie Curie in 1898. Discovered mixed
with uranium. Shared 1903 Nobel Prize
with Henri Becquerel.
 Million times more radioactive than
uranium.
226


Radium dust mixed with water
and glue used to make
radioluminescent paint during
1920’s: watch dials, instruments.
88
Ra
Early Application
When a radium atom decays, one of the
particles it ejects (an alpha particle) hits a
phosphor molecule in the surrounding
paint that the manufacturer used to paint
the watch dial's numbers.
 Then the phosphor glows a
faint blue-green light.


The radium, however, does
not glow; only the phosphor
glows.
Radium Girls
U.S. Radium Corporation
Orange, NJ, ca.1920
Radium Girls
The employees hired to paint the dials were
mostly young women. Paint was applied
with a small brush.
 The women "pointed" the brushes on their
tongues between applications, and ingested
a small quantity of radium each time.


“But everyone knew the stuff was harmless. The
women even painted their nails and their teeth to
surprise their boyfriends when the lights went out.
Danger to Radium Girls
Radium is chemically similar to calcium,
and is therefore a “bone seeker.” It emits
alpha-particles.
 226Ra that accumulated in the bone marrow
irradiated nearby tissue, and produced
bone cancer and other genetic damage.
 Curie herself died of radium poisoning in
1934.


The right of individual workers to sue for damages from corporations
due to labor abuse was established as a result of the Radium Girls
case. See article.
Products of Radioactivity

Decay in three common ways:
 Emit alpha particles:
Helium nuclei (2 protons, 2
neutrons).

Emit beta particles:
Electrons.

Emit gamma rays:
High energy photons.
α
β
γ
Half-Life
Half-life is the time it takes for half of the
nuclei of a sample to decay.
 Radioactive isotopes have characteristic
half-lives.

50 g of
other atoms
100 g of X
First half life
75 g of
other atoms
Second half life
50 g of X
25 g of X
Example Half-Lives
Carbon-14
5,730 years
Cobalt-60
5.26 years
Strontium-90
29.12 years
Radium-226
1600 years
α decay to 222Rn (radon)
Uranium-238
4.46 billion years

Uranium-235
703 million years
After cigarettes,
radon is the
second leading
cause of lung
cancer. − EPA
Amount of substance, in %
Quantity of Radioisotope
100
50
25
0
Years, in half-lives
Lise Meitner
Fission
1
0
Otto Hahn

Large unstable nucleus splits into two
intermediate-size nuclei, emits neutrons.

Example: Uranium-235 fission. Bombard
with one low-energy “thermal” neutron
(Otto Hahn and Lise Meitner experiment).
235
142
92
56
n+ U
92
1
36
0
Ba + Kr +2 n
- one of several U-235 decay processes
U-235 Fission
142
Missing Mass
Element or
Particle
Before
After
U-235
n
Ba-142
Kr-92
2n
Mass Difference
Mass
Total
(in units of amu,
1.660x10-27 kg)
235.043924
1.008665
141.916453
91.926156
2.017330
236.052589
235.859939
–0.19265 amu
~3.2x10–28 kg
How Masses Add Up
Resulting masses are lighter.
 Where did the mass go?


Lise Meitner proposed that it goes into
energy from Einstein’s equation E = mc2.
Mass Difference =
mc2 = (0.19265)c2 =
–3.2x10–28 kg
–180 MeV
Summary
One neutron absorbed by U-235,
momentarily becomes U-236, unstable,
and splits into smaller atoms with
tremendous kinetic energy (Coulomb
repulsion) (~200 MeV) plus a few
neutrons.
 Visualize with Niels Bohr water drop
model.

Fission
Critical Mass
When the process is self-sustaining, the
sample has a critical mass.
 For every 2 or 3 neutrons released, at
least one must strike another uranium
nucleus.
 If less than 1, then the reaction will die
out.
 Greater than one it will grow unless
controlled (chain reaction).

Controlled Reaction

Slow Fission Down!
 A control rod (neutron-absorbing element
boron or cadmium) absorbs a large
number of neutrons in the reaction.

Speed Fission Up!
 Fission works best with slow neutrons.
 Need a moderator (e.g., graphite, water)
to slow down high-speed neutrons that
are created.
Warnings
Aug 2, 1939
Einstein to
FDR.
 Possibility
that Nazis
were
developing an
atomic bomb.

First Controlled Fission
December 2, 1942.
 Enrico Fermi, University of Chicago.
 Natural uranium, cadmium control rods.
 315 tons of graphite used as a moderator
to slow down the neutrons.

Manhattan Project
In an atomic bomb, a mass of fissile
material greater than the critical mass
must be assembled instantaneously.
 Held together for about a millionth of a
second to permit the chain reaction to
propagate before the bomb explodes

Manhattan Project
Hiroshima
“Little Boy,” dropped on Hiroshima, Japan,
August 8, 1945.
 Explodes 1,900 feet above city.
 140,000 people die immediately.
 Equivalent to 13 kilotons of dynamite.
 Used 60 kg (132 lbs) of U-235.
 August 15, 1945, Japan announces
surrender, ending WWII. (Germany had
surrendered May 7, 1945)

Hiroshima
Nuclear Tests in Nevada
 Interview
Controlled Nuclear Power
Three-Mile Island,
Middletown, PA
Nuclear Power Plant
Light and Heat
Energy
Mechanical
Energy
Nuclear
Energy
Thermal
Energy
Electrical
Energy
Nuclear Fuel Life Cycle
Uranium
enrichment
centrifuges
Enrichment
Ore Processing
Uranium Mine
Cameco Corp.'s uranium mine in
northern Saskatchewan
Fuel Production
Power Reactor
Used Fuel Disposal
Road transport of spent fuel in
Japan
Nuclear Waste
Percent
Radioactive
Waste
Percentofof
Radioactive
Worldwide
Waste
Worldwide
High Level
3%
Percent of Total
Radioactivity
Low Level
1%
Intermediate
Level
7%
Low Level
90%
High Level
95%
Intermediate
Level
4%
High-Level Waste
Thermally hot, highly radioactive, and
potentially harmful used nuclear reactor
fuel.
 Converted into granules and mixed with
molten glass and stored. Licensees must
safely store this fuel at their reactors.
 Disposal of high-level radioactive waste
was defined by the Nuclear Waste Policy
Act of 1982.

High-Level Waste

Nuclear Waste Policy Act of 1982: Dispose highlevel waste at Yucca Mountain, Nevada.






80 miles northwest of Las Vegas, NV.
No official date for opening the $12 billion facility.
3/7/09 Obama proposed budget closed the
facility. Satisfies Harry Reid (D-Nev).
What to do with existing 57,000 tons of highly
toxic waste at 121 above-ground sites?
Existing plants create 2,000 tons each year.
DOE study underway to find an alternative.
Low-Level Waste
Slightly radioactive.
 Includes things like protective clothing,
laboratory equipment, paper towels,
gloves, etc. Hospital, industry waste.


Compacted using a high
force compactor. Bury in
shallow pits.
WIPP
Forbes, 2/13/12 p. 91.

Waste Isolation Pilot Project
(WIPP), Carlsbad, NM, is
the nation’s only permanent,
deep geologic repository for
nuclear waste.

Storage for radioactive
drums with the plutoniumladen detritus of America’s
nuclear weapons program.

3,000-ft salt layer.
Clean Nuclear Process?
Are there heavier elements that can be
fused into a lighter element (so missing
mass goes off as E=mc2 energy)?
 Fusion energy would be “clean.” No
radioactive waste products.

n
Binding Energy per Nucleon
Isotopes of Hydrogen

Hydrogen
1
1

Deuterium
 “Heavy hydrogen D2O.”
 Abundant in oceans (1
in 6,500 molecules is
“heavy water.”
2
1
H
D
Fusion
n
Candidate Fusion Equation
Isotopes of Hydrogen
 Deuterium
D

2
1
2
3
1
2
D+ D
1
He + n
0
Fusion Process
Element or
Particle
Before
After
Deuterium
Deuterium
Helium-3
n
Mass
Difference
Δmc2
Mass
Total
(in units of amu,
1.660539x10-27 kg)
2.014103
2.014103
3.016029
1.008665
4.028206
4.024694
-0.003512
amu
-3.3 MeV
Example Construction
Lithium and Deuterium
H-Bomb.
 Must overcome
Coulomb repulsion, get
close enough for
strong nuclear force to
take over.
 Fission bomb provides
energy to bring them
close to each other.

Castle Bravo Test
15 Megatons (equivalent of dynamite).
 February 28, 1954, Bikini Atoll in South
Pacific.

 “One
of the atolls has been totally
vaporized, disappearing into a gigantic
mushroom cloud that spread at least 100
miles wide and dropping back to the sea
in the form of radioactive fall-out.”
15 Megatons.
February 28, 1954, Bikini Atoll in South Pacific.
Big Ivan
Tsar Bomba
“Big Ivan,” the largest bomb ever tested,
October 30, 1961
 Commissioned by Nikita Kruschev.
 Exploded with 50-Megaton force.
 Burst at 13,000 feet, fireball reached the
Earth.
 Designed so delivery aircraft could safely
fly 25 miles away before detonation.
 Film

Controlled Fusion
Need kinetic energy to overcome Coulomb
repulsion.
 National Ignition Facility




Inertial confinement fusion experiments.
Implode a microcapsule simultaneously
irradiated by 192 giant lasers.
Facility certified to operate March 27, 2009.
NIF: Recipe for a Small Star






Hollow, spherical plastic capsule about two millimeters in
diameter (about the size of a small pea)
Filled with 150 micrograms of a mixture of deuterium and
tritium, the two heavy isotopes of hydrogen.
Take a laser that for about 20 billionths of a second can
generate 500 trillion watts – the equivalent of five million
million 100-watt light bulbs.
Focus all that laser power onto the surface of the
capsule.
Wait ten billionths of a second.
Result: one miniature star.
Controlled Fusion
International approach under construction.
 International Thermonuclear Experimental
Reactor (ITER), located in southern France.
 Magnetic confinement fusion
experiments.
 Contain plasma in
magnetic fields while
energy is added.

Impact on Humans

Dosimeters – used to measure radiation.
Radiation Impact on Humans
Passage of an
energetic charged
nuclear particle
through a cell
produces a region of
dense ionization
along its track.
 Destroys or
damages DNA.

DNA Radiation Damage
– artist concept
Radiation Dosage
Radiation dosage is the energy deposited
per kilogram of living tissue.
 Traditional U.S. unit is rad (radiation
absorbed dose), 0.01 J per kilogram of
living tissue.
 Does not make a distinction between
various types of radiation and the resulting
damage.

RBE Damage to Humans
RBE (relative biological effectiveness).
 Photon (x-ray and γ-ray) radiation and β
radiation are assigned the base value of 1.
 RBE for neutron radiation has the value of
10.
 RBE for alpha-particle radiation has the value
of 20.
 Thus, 1 rad of alpha radiation is 20X more
damaging than 1 rad of X-rays.

Radiation Therapy
Injure or destroy cells in the area being
treated (the “target tissue”) – damage their
genetic material, making it impossible for
these cells to continue to grow and divide.
 Damages both cancer cells and normal
cells –most normal cells can recover from
the effects of radiation.
 Radiation therapy – damage as many
cancer cells as possible, while limiting
harm to nearby healthy tissue.

Treatment Types

External radiation therapy
 X-rays and gamma rays.
 Particle beams.

LLUMC“Proton Treatment Center.”
 Proton treatment deposits energy in
very small region, protecting organs in
front of and behind the target.
Treatment Types
Radioactive implants are devices that are
placed directly within cancerous tissue or
tumors, in order to deliver radiation
therapy intended to kill cancerous cells.
 With use of radioactive implants, tumor is
subjected to radioactive activity over a
longer period of time, as compared to
external beam therapy.

Permanent Brachytherapy
Doctor implants radioactive (iodine125 or palladium-103) seeds into
the prostate gland. Anywhere from 40 to
100 seeds are commonly implanted.
 The implants remain in place permanently,
and become biologically inert (no longer
useful) after a period of months. This
technique allows a high dose of radiation
to be delivered to the prostate with limited
damage to surrounding tissues.

Isotopes of Hydrogen
Hydrogen (in “light water”
H2O)
 Deuterium
 “Heavy hydrogen.”
 Stable isotope
 Tritium
 Radioactive isotope of
hydrogen.
 Half-life = 4,500 days

1
1
2
1
H
H
3
1
H
Paper can block
Use aluminum to
block
Use lead to block
A Nuclear Decay Chain

The natural decay chain of uranium-238 is as follows:














decays, through alpha-emission, with a half-life of 4.5 billion years to thorium-234
which decays, through beta-emission, with a half-life of 24 days to protactinium-234
which decays, through beta-emission, with a half-life of 1.2 minutes to uranium-234
which decays, through alpha-emission, with a half-life of 240 thousand years to thorium-230
which decays, through alpha-emission, with a half-life of 77 thousand years to radium-226
which decays, through alpha-emission, with a half-life of 1.6 thousand years to radon-222
which decays, through alpha-emission, with a half-life of 3.8 days to polonium-218
which decays, through alpha-emission, with a half-life of 3.1 minutes to lead-214
which decays, through beta-emission, with a half-life of 27 minutes to bismuth-214
which decays, through beta-emission, with a half-life of 20 minutes to polonium-214
which decays, through alpha-emission, with a half-life of 160 microseconds to lead-210
which decays, through beta-emission, with a half-life of 22 years to bismuth-210
which decays, through beta-emission, with a half-life of 5 days to polonium-210
which decays, through alpha-emission, with a half-life of 140 days to lead-206, which is a
stable nuclide.
- Wikipedia
Carbon Dating
Carbon Dating
Trace amounts of Carbon-14 are present in
all organic materials.
 Created by the Sun in Earth’s upper
atmosphere and mixed through atmosphere
in CO2.
 Absorbed by all living things. When the living
body dies, the amount in the body is “fixed.”
 Half-life of 14C is 5,730 years.
 Measure the ratio of 12C to 14C to estimate
age.

Example

Bones were found in Texas that had only
25% of their carbon-14 left. Estimate their
age.
Half was lost in the first 5,730
years: down to 50%
 Half of what was left was lost in
the next 5,730 years, down to
25%.
 Total elapsed time is
approximately 11,460 years.

Example Carbon−14
Carbon-14
5,730 years
Cobalt-60
5.26 years
Strontium-90
29.12 years
Radium-226
1600 years
Uranium-238
4.46 billion years
Uranium-235
703 million years
14C
Decay
β decay to 14N