Nuclear Physics and Radiation Hazards
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FE
covers
Lectures 23 – 36
•
The study guide, formulas, and practice
final exam questions are posted on the
Exam Information Link below.
•
We will review the practice final exam
questions on Wed. Dec. 10, and Friday
Dec. 12.
L 36 Modern Physics - 4
•
Nuclear physics
–
what’s inside the nucleus and what
holds it together
–
what is radioactivity, half-life
–
carbon dating
•
Nuclear energy
–
nuclear fission
–
nuclear fusion
–
nuclear reactors
–
nuclear weapons
2
Radioactivity
•
Some nuclei are unstable and spontaneously
emit particles at random times
–
Alpha particles (helium nucleus)
–
Beta particles – energetic electrons
–
Gammas - energetic photons (higher than x-rays)
•
The beta particles (electrons) come from a
process called
beta decay,
in which a neutron
decays into a proton, an electron and an
antineutrino (note that charge is conserved!)
3
mass =
240.06
units
mass =
239.86
units
The extra mass is converted into kinetic
energy, which is mostly in the neutrons.
Energy is released in the fission (breakup) of a
heavy nucleus by fast neutron bombardment
4
Nuclear reactions: E = mc
2
Biological effects of nuclear radiation
•
Nuclear reactions can produce alphas, betas,
neutrons and gamma radiation (particles or
photons)
•
Nuclear radiation is ionizing radiation, i.e.,
energetic enough to knock electrons out of
atoms or molecules
•
Ionizing radiation
is potentially harmful to
humans because the ionization it produces can
alter significantly the structure of molecules
within a living cell which can lead to alterations
of the cell (make them cancerous) or to the
death of the cell
5
Hazards of radiation
•
The hazards of radiation can be minimized
by limiting overall exposure
•
The effects of absorbed doses or ionizing
radiation is measured in a unit called the
rem.
•
The effects of radiation exposure are
–
Short term or acute effects appearing within a
matter of minutes of exposure
–
Long-term effects that may appear in years,
decades or even in future generations
6
Average radiation doses received
by a
US
resident
Source of radiation
dose in mrem/yr*
Natural Background radiation
Cosmic rays…...............................28
Earth and air……………………….28
Internal radioactive nuclei………..39
Inhaled radon…………………….200
Man-made radiation
Medical / dental x-rays……………39
Nuclear medicine………………….14
*Current federal standards limit exposure to 500 mrem/yr
7
Radiation sickness
•
This is the general term applied to the
acute effects of radiation
•
A dose less than 50 rem causes no short
term ill effects
•
A dose of 50 – 300 rem
at one time
brings
on radiation sickness
•
A whole body dose of 400 – 500 rem is
lethal for about 50% of people exposed
•
Whole body doses greater than 600 rem
results in death for almost all individuals
8
Nuclear Physicists
9
Energy from the nucleus
•
Huge amounts of energy are given off in two
nuclear processes
–
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heavy nucleus in two
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light nuclei into one
10
A lot of energy from a little mass
•
The energies released when a large nucleus
undergoes fission or small nuclei undergo fusion
are enormous compared to chemical energies
(e.g. burning fossil fuel)
•
When Uranium splits apart about 0.1% of its
mass is converted into energy
•
Pound for pound, nuclear reactions release
about 10 million times more energy than
chemical reactions
•
1 pound Uranium
1 million gallons of gasoline
11
Splitting the atom
Nuclear Fission
•
To split a uranium
nucleus apart takes
energy
•
A neutron hitting a
uranium nucleus can
cause it to split
•
A neutron can split U-
235 into Cs-143 and
Rd-90 plus a
few
extra neutrons
12
The nuclear chain reaction
•
When U-235 splits, on
average 2.5 neutrons are
released
•
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This can result in a
catastrophic process
with enormous energy
released.
13
Reactor
or
Bomb
•
If the energy released in a nuclear chain
reaction is allowed to proceed in a
controlled
way, then this can be used as
an energy source
nuclear reactor
•
If the chain reaction occurs in an
uncontrolled
manner then you have
atomic bomb
•
Enrico Fermi produced the first nuclear
reactor under the west stands of Stagg
Field at the University of Chicago in 1942
14
Electricity generation by nuclear power
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Percentage of electricity
produced by nuclear power
France: 77%
Belgium: 54%
Slovakia: 54%
Switzerland: 41%
Sweden: 36%
USA: 19%
Germany: 18%
Japan: 18%
Russia: 18%
UK: 16%
Canada: 15%
Argentina: 7%
China: 2%
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Nuclear reactors
•
The fuel elements contain the
fissile fuel in the form of rods of
1 cm diameter. There may be
thousands of such rods stacked together
in the reactor core
•
The most common fuel is enriched U-235
•
Some type of moderator material is also
used to slow down the neutrons to make
their capture more efficient
16
A nuclear power plant
Nuclear
reactor
Electric
generator
Electric
transmission
17
Reactor operation
•
The reactor is usually operated in the so-
called
critical
state in which each fission
leads to only one additional fission.
•
In the critical state the reactor produces a
steady output of electrical energy
•
The reactor is designed not to go into the
supercritical
state – in this state the
reactor produces an uncontrolled and
increasing amount of energy which can
cause it overheat and lead to meltdown.
18
Controlling the nuclear reactor
•
To keep the reactor in the critical state the
operators adjust the
control rods
•
The control rods can be moved into or out of the
reactor core. They contain an element, such as
cadmium or boron which absorbs neutrons.
•
If the reactor is getting too hot, the control rods
are pushed into the core to slow down the chain
reaction
•
The heat generated within the fuel rods is
carried away by water surrounding the rods
19
Reactor core
•
To start the reactor,
the control rods are
pulled out of the
core
•
To stop the reactor,
the control rods are
pushed into the
core
•
Inside a concrete
containment vessel
20
Pros and Cons of Nuclear energy
ADVANTAGES
•
Plentiful fuel
•
no greenhouse gases
•
no poisonous
emissions
•
non-polluting
•
efficient power
production
DISADVANTAGES
•
must deal with nuclear
waste
•
possibility of
catastrophic accident
with long term effects*
•
expensive to build
•
can be used to enrich
uranium for bombs
* -- US – 1979, Three mile Island, Pennsylvania
-- World- 1986, Chernobyl, Ukraine (80 killed within one week of accident)
-- Japan -2011 caused by Tsunami
negative spin – big disaster – no more nuclear power plants
positive spin – even with Tsunami, no one killed, build more plants
21
22
The atomic (fission) bomb
•
a critical mass of fissionable material is needed
•
Natural uranium contains
238
U and 0.7%
235
U, but
only
235
U is fissionable. In the enrichment process,
the
235
U and
238
U are separated. Weapons-grade
uranium requires enrichment to > 20%.
•
if a critical mass can be achieved than an self-
sustained uncontrolled reaction occurs
•
To achieve critical mass (60 kg), 2 lumps (7 inch
diameter ball ) of a non-critical mass of U-235 are
brought together quickly using a cannon
•
When the U-235 becomes supercritical, a
catastrophic fission will quickly turn into a fireball
23
24
Little Boy (Uranium bomb)
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Nuclear Fusion
Two light nuclei (D & T)
are combined into one
(He) with a large release
of energy
If this is done with a
a large number of nuclei,
the energy is released
catastrophically as
a
Hydrogen Bomb
26
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B
o
m
b
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A fusion bomb releases energy by
fusing deuterium with tritium nuclei
to form helium and neutrons
•
To achieve this, the hydrogen must
be heated to 100 million C using a
fission bomb
thermonuclear
•
Thermonuclear fusion is what
powers the stars
27
H bomb
Effects of a nuclear explosion
•
The released neutrons produce the fireball
by heating everything around them
•
The ultra hot fireball produces an intense
flash of light, x-rays and gamma rays
•
The explosion creates a huge pressure
surge
blast wave that flattens
everything within miles of ground zero
•
Long after the blast there is the fallout
the creation and release of radioactive
nuclei that are carried away in the air
28
Controlled
thermonuclear fusion
•
Nuclear reactor using
nuclear fusion energy
•
Safer than fission reactor
•
Fuel (D, T) can be
obtained from seawater
•
Will heat Tritium gas to
100,000,000 K
•
Test reactor being built in
France; collaboration of
seven countries: EU, IN,
JP, CH, RU, SK, US.
29
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We will review the practice final
exam questions on Wed. Dec. 10,
and Friday Dec. 12.
Exploring the world of nuclear physics, this content covers topics like nuclear reactions, radioactivity, biological effects of nuclear radiation, and hazards of radiation exposure. It delves into the structure of the nucleus, radioactivity processes, nuclear energy, and the biological impacts of ionizing radiation. The content emphasizes the importance of minimizing radiation exposure to mitigate both short-term and long-term effects on human health.
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PHYS:1200 FINAL EXAM FINAL EXAM: Wednesday December 17, 12:30 P - 2:30 P in LR-1 VAN FE covers Lectures 23 36 The study guide, formulas, and practice final exam questions are posted on the Exam Information Link below. We will review the practice final exam questions on Wed. Dec. 10, and Friday Dec. 12. 1
L 36 Modern Physics - 4 Nuclear physics what s inside the nucleus and what holds it together what is radioactivity, half-life carbon dating Nuclear energy nuclear fission nuclear fusion nuclear reactors nuclear weapons 2
Radioactivity Some nuclei are unstable and spontaneously emit particles at random times Alpha particles (helium nucleus) Beta particles energetic electrons Gammas - energetic photons (higher than x-rays) The beta particles (electrons) come from a process called beta decay, in which a neutron decays into a proton, an electron and an antineutrino (note that charge is conserved!) n o 1 4 2 He + + + 1 1 p e 3
Nuclear reactions: E = mc2 Energy is released in the fission (breakup) of a heavy nucleus by fast neutron bombardment 239 94Pu + + + 1 0 239 94 96 38 143 56 1 0 n Pu Sr Ba n mass = 240.06 units mass = 239.86 units The extra mass is converted into kinetic energy, which is mostly in the neutrons. 4
Biological effects of nuclear radiation Nuclear reactions can produce alphas, betas, neutrons and gamma radiation (particles or photons) Nuclear radiation is ionizing radiation, i.e., energetic enough to knock electrons out of atoms or molecules Ionizing radiation is potentially harmful to humans because the ionization it produces can alter significantly the structure of molecules within a living cell which can lead to alterations of the cell (make them cancerous) or to the death of the cell 5
Hazards of radiation The hazards of radiation can be minimized by limiting overall exposure The effects of absorbed doses or ionizing radiation is measured in a unit called the rem. The effects of radiation exposure are Short term or acute effects appearing within a matter of minutes of exposure Long-term effects that may appear in years, decades or even in future generations 6
Average radiation doses receivedby a US resident Source of radiation dose in mrem/yr* Natural Background radiation Cosmic rays ...............................28 Earth and air .28 Internal radioactive nuclei ..39 Inhaled radon .200 Man-made radiation Medical / dental x-rays 39 Nuclear medicine .14 *Current federal standards limit exposure to 500 mrem/yr 7
Radiation sickness This is the general term applied to the acute effects of radiation A dose less than 50 rem causes no short term ill effects A dose of 50 300 rem at one time brings on radiation sickness A whole body dose of 400 500 rem is lethal for about 50% of people exposed Whole body doses greater than 600 rem results in death for almost all individuals 8
Nuclear Physicists Otto Hahn and Lise Meitner discovered fission. Only Hahn won the Nobel Prize. Meitner should also have won. Marie Curie discovered radioactivity. First woman to win a Nobel Prize. Won 2 Nobel prizes in Physics and Chemistry. Enrico Fermi Father of the Atomic bomb Won Nobel prize for discovering new radioactive elements. Edward Teller Father of the Hydrogen bomb Convinced Pres. Reagan to pursue the Star Wars project. 9
Energy from the nucleus Huge amounts of energy are given off in two nuclear processes Nuclear fission: splitting a heavy nucleus in two Nuclear fusion: fusing two light nuclei into one 10
A lot of energy from a little mass The energies released when a large nucleus undergoes fission or small nuclei undergo fusion are enormous compared to chemical energies (e.g. burning fossil fuel) When Uranium splits apart about 0.1% of its mass is converted into energy Pound for pound, nuclear reactions release about 10 million times more energy than chemical reactions 1 pound Uranium 1 million gallons of gasoline 11
Splitting the atom Nuclear Fission To split a uranium nucleus apart takes energy A neutron hitting a uranium nucleus can cause it to split A neutron can split U- 235 into Cs-143 and Rd-90 plus a few extra neutrons 12
The nuclear chain reaction When U-235 splits, on average 2.5 neutrons are released These neutrons can then go on to cause other U- 235 s to split, this resulting in a chain reaction This can result in a catastrophic process with enormous energy released. 13
Reactor or Bomb If the energy released in a nuclear chain reaction is allowed to proceed in a controlled way, then this can be used as an energy source nuclear reactor If the chain reaction occurs in an uncontrolled manner then you have atomic bomb Enrico Fermi produced the first nuclear reactor under the west stands of Stagg Field at the University of Chicago in 1942 14
Electricity generation by nuclear power Percentage of electricity produced by nuclear power France: 77% Belgium: 54% Slovakia: 54% Switzerland: 41% Sweden: 36% USA: 19% Germany: 18% Japan: 18% Russia: 18% UK: 16% Canada: 15% Argentina: 7% China: 2% Nuclear Power Plant Steel and Concrete Containment vessel 15
Nuclear reactors The fuel elements contain the fissile fuel in the form of rods of 1 cm diameter. There may be thousands of such rods stacked together in the reactor core The most common fuel is enriched U-235 Some type of moderator material is also used to slow down the neutrons to make their capture more efficient 16
A nuclear power plant Electric transmission 17 Electric generator Nuclear reactor
Reactor operation The reactor is usually operated in the so- called critical state in which each fission leads to only one additional fission. In the critical state the reactor produces a steady output of electrical energy The reactor is designed not to go into the supercritical state in this state the reactor produces an uncontrolled and increasing amount of energy which can cause it overheat and lead to meltdown. 18
Controlling the nuclear reactor To keep the reactor in the critical state the operators adjust the control rods The control rods can be moved into or out of the reactor core. They contain an element, such as cadmium or boron which absorbs neutrons. If the reactor is getting too hot, the control rods are pushed into the core to slow down the chain reaction The heat generated within the fuel rods is carried away by water surrounding the rods 19
Reactor core To start the reactor, the control rods are pulled out of the core To stop the reactor, the control rods are pushed into the core Inside a concrete containment vessel 20
Pros and Cons of Nuclear energy ADVANTAGES Plentiful fuel no greenhouse gases no poisonous emissions non-polluting efficient power production DISADVANTAGES must deal with nuclear waste possibility of catastrophic accident with long term effects* expensive to build can be used to enrich uranium for bombs * -- US 1979, Three mile Island, Pennsylvania -- World- 1986, Chernobyl, Ukraine (80 killed within one week of accident) -- Japan -2011 caused by Tsunami negative spin big disaster no more nuclear power plants positive spin even with Tsunami, no one killed, build more plants21
The atomic (fission) bomb a critical mass of fissionable material is needed Natural uranium contains 238U and 0.7% 235U, but only 235U is fissionable. In the enrichment process, the 235U and 238U are separated. Weapons-grade uranium requires enrichment to > 20%. if a critical mass can be achieved than an self- sustained uncontrolled reaction occurs To achieve critical mass (60 kg), 2 lumps (7 inch diameter ball ) of a non-critical mass of U-235 are brought together quickly using a cannon When the U-235 becomes supercritical, a catastrophic fission will quickly turn into a fireball 23
Nuclear Fusion Two light nuclei (D & T) are combined into one (He) with a large release of energy If this is done with a a large number of nuclei, the energy is released catastrophically as a Hydrogen Bomb 26
The Hydrogen (thermonuclear fusion) Bomb A fusion bomb releases energy by fusing deuterium with tritium nuclei to form helium and neutrons To achieve this, the hydrogen must be heated to 100 million C using a fission bomb thermonuclear Thermonuclear fusion is what powers the stars H bomb 27
Effects of a nuclear explosion The released neutrons produce the fireball by heating everything around them The ultra hot fireball produces an intense flash of light, x-rays and gamma rays The explosion creates a huge pressure surge blast wave that flattens everything within miles of ground zero Long after the blast there is the fallout the creation and release of radioactive nuclei that are carried away in the air 28
Controlled thermonuclear fusion Nuclear reactor using nuclear fusion energy Safer than fission reactor Fuel (D, T) can be obtained from seawater Will heat Tritium gas to 100,000,000 K Test reactor being built in France; collaboration of seven countries: EU, IN, JP, CH, RU, SK, US. International Thermonuclear Experimental Reactor (ITER) 29
We will review the practice final exam questions on Wed. Dec. 10, and Friday Dec. 12. 30
