Isotopes
Isotopes = 2 atoms of the
same element (same #
of protons / atomic # )
that have different
numbers of__________.
Since the number of
_________ is different,
the isotopes have
different __________.
The number given after
the element symbol is the
atomic mass.
Examples:
• 3 isotopes of H2O
• Carbon-12 & Carbon-14 (12C & 14C)
• U-235 & U-238
Nuclear Fission
nuclear fission: (fission = to split) a nuclear change
in which certain unstable isotopes of high mass
numbers split into lighter nuclei & ______________
in the process.
Fission of a
uranium–235
nucleus,
initiated by a
neutron.
Half-Life: The amount of time that
it takes half of a radioactive sample
to decay.
Determining amount of radioactive
isotope remaining
1 half-life
2 half- lives
3 half-lives
4 half-lives
½ (1/21)
___ (1/22)
___ (1/23)
___ (1/24)
Formula: N = No (0.5)t
t= number of half-lives
N = amount left No = original amount
Half-life Comparisons
Radioisotope
Half-life
Berillyium-11
13.81 seconds
Iodine-131
8 days
Stronium-85
11 years
Tritium (Hydrogen-3)
12 years
Uranium-235
700 million years
Uranium-238
4.5 billion years
Radioactive Decay
Unstable isotopes undergo decay to form other isotopes,
& in the process energy is emitted in three forms:
• alpha particles: fast–moving, _______________
(= Helium nucleus)
• beta particles: fast–moving, ________________
• gamma rays: high–energy__________________
Alpha Decay
Alpha particles can be blocked most easily, since they
are _________ than beta particles.
Gamma rays are the most difficult form of radiation to
block, since they are not composed of matter, but rather
are high frequency electron radiation.
2 Types of Beta Decay
Beta minus decay: A neutron decays into a
__________________ with the electron emitted.
Beta Minus Decay
Beta Plus Decay
Beta plus decay: A proton decays into a ______
______________with the positron emitted. (Like
an electron, a positron has no significant mass.)
Discuss with your table partner:
Review the type of particles released in alpha, beta
minus and beta plus decay (and what particles
breakdown for beta decay). Determine what new
isotope would be produced in each of the examples of
radioactive decay on the next three slides.
Plutonium-236 (atomic number 94) undergoes alpha decay.
What is the atomic number of the new isotope? ____
What is atomic mass of the new isotope? ____
New isotope: _________________
Magnesium-23 (atomic # 12) undergoes beta plus decay.
What is the atomic number of the new isotope? ___
Why? _______________________
What is atomic mass of the new isotope? ___
New isotope: ___________
Carbon-14 (atomic number 6) undergoes beta minus decay.
What is the atomic number of the new isotope? __
Why? ______________________
What is atomic mass of the new isotope? __
______________
New isotope:
Radioactive Pathway:
A radioactive isotope can undergo
a series of radioactive decay, until
a stable isotope is reached.
Increasing frequency and energy
Increasing wavelength
Gamma Rays are very high energy waves with a short wavelength
Radiation Intensity is inversely related to the
distance from the source:
Intensity α 1/r2 (r = radial distance from source)
Radioactivity Units
Radioactivity Absorbed
Dose
Equivalent
Dose
Common
Units
SI Units
Exposure
Curie (Ci)
rad
rem
Roentgen (R)
Bequerel
(Bq)
Gray
(Gy)
Sievert
(Sv)
Coulomb/
Kilogram (C/kg)
• Some conversions: 1 Curie = 3.7 x 1010 disintegrations/sec
1 millicurie = 37 megabequerel (1 Bq = 1 disintegration/sec)
1 coulomb/kg = 3880 Roentgen
• Average dose per person/year (US) = 360 mrem/yr (millirem/yr)
• International Standard for safe yearly dose = 5,000 mrem/yr =
5 rem/yr (for people who work around radioactivity)
Sources of Radiation:
• Cosmic: from sun and other
stars
• Terrestrial: decay of radioactive
elements in ground. Common
decay product is radioactive
radon gas
• Food has Carbon 14
•Medical: X-rays, CT
scans…
•Coal plants release some
radioactivity
Nuclear Chain Reactions
nuclear chain reaction: multiple fissions
resulting from a _________ feedback loop in
which each fission releases neutrons that cause
more fissions to occur.
A nuclear chain reaction
leads to major release
of energy in the form of
heat (and light).
Nuclear Energy
Nuclear fission reactors produce
electricity from heat released by
the fission of uranium–235 or
plutonium–239.
• controlled rate of fission by
absorbing excess neutrons
with _________ & surrounding
the reaction core with_______;
• built–in safety features are
supposed to minimize the risk
of release of radioactive
substances or an out-of-control
fission reaction.
Nuclear Reactor: Light-Water Reactor
•Small amounts of
radioactive gases
•Uranium
•fuel input
•(reactor core)
•Control rods
•Containment
shell
•Heat
•Waste
exchanger heat
•Turbine
•Steam
•Hot
coolant
•Pump
•Pump
•Shielding
•Pressure vessel
•Generator
•Coolant
•Moderator
•Coolant
passage
•Periodic removal and storage of
radioactive wastes and spent fuel
assemblies
•Pump
•Pump
•Hot
water
output
•Cool
water
input
•Useful electrical
energy
•25%–30%
•Waste heat
•Water •Condenser
•Periodic removal and
storage of radioactive
liquid wastes
•Water source (river,
lake, ocean)
Nuclear Energy Use
In United States, nuclear energy
is declining.
•No new plants since ______ .
Although, first permits in decades
is underway for two plants.
•Existing plants (105) retired by
2030.
Some other countries are
investing increasingly in nuclear
energy.
• France gets about 78% of its
energy from nuclear power
plants.
Nuclear Accidents: Three Mile Island
On March 29, 1979, reactor at the
Three Mile island nuclear plant near
Harrisburg, PA, lost its coolant & the
core suffered a _________________.
• 50,000 people evacuated & another
50,000 fled area;
• unknown amounts of radioactive
materials were released; an
estimated 15-24 curies of I-131
•partial cleanup & payment of
damage claims cost $1.2 billion
so far;
•1997 study concluded that
increased cancer rates were
caused by released radiation.
Nuclear Accidents: Chernobyl
On April 26, 1986, Chernobyl disaster in the Ukraine:
a series of explosions in a nuclear reactor flung
radioactive debris into the atmosphere.
Chernobyl
• About 400,000 people were forced to leave their homes
• According to a UN report, some 160,000 km2 (62,000
mi2) remain contaminated;
• About 35-49 million Curies of I-131 was released
Chernobyl Zone of Exclusion
The zone of exclusion is _________, which is
the size of __________________.
Chernobyl
• In 1998 the Ukrainian
health ministry reported
3,576 deaths.
However, Greenpeace
estimates a total death
toll of about 32,000;
• Over ___________
people were exposed to
dangerous levels of
radioactivity;
• The cost of the incident
is estimated in excess
of $358 billion.
Nuclear Accidents: Fukishima Dai-ichi
• On March 11, 2011, a 9.0 earthquake
hit off the coast of Japan, creating a
13-15 m (43-49 foot) tsunami wave.
• Electricity from Japan’s grid was lost,
but emergency generators came online to power the cooling systems.
• A tsunami flowed over the 5.7 m
seawall at the plant _____________
___________________________.
• The fuel in the reactors began to
over-heat.
• 12 mile exclusion zone
• 80,000 people displaced
• Over 1,600 employees exposed to
high levels of radiation.
Nuclear Accidents: Fukishima Dai-ichi
The explosions
sent large
amount of
radioactive
elements into the
atmosphere
http://www.cbsnews.
com/830118563_16257395780/a-rarelook-at-thefukushima-daiichino-go-zone/
Nuclear Accidents: Fukishima Dai-ichi
The coolant leaking
out of the cores
contaminated
ground water and
ocean water.
The extent of ocean radiation
contamination as of Oct., 2011
Nuclear Fuel Cycle
•Decommissioning
of reactor
•Fuel assemblies
•Enrichment
•Fuel fabrication
of UF6
•Reactor
•(conversion of enriched UF6 to
UO to UO2 and fabrication of
fuel assemblies)
•Conversion
of U3O8
•to UF6
•Uranium-235 as UF6
Plutonium-239 as PuO2
•Temporary storage of spent
fuel assemblies underwater
or in dry casks
•Spent fuel
reprocessing
•Low-level radiation
with long half-life
•Geologic disposal
of moderate- and
high-level
radioactive wastes
•Open fuel cycle today
•Recycling of nuclear fuel
Long Term Storage Issues
After 3 or 4 Years in a Reactor, Spent Fuel Rods
Are Removed and Stored in Water
Storage of Nuclear Waste
• Storing nuclear waste is the ultimate NIMBY situation (Not
In My Back Yard)
• Until a long-term location is opened, nuclear waste remains
stored at ___________________
• Short-term storage involves keeping waste submerged in
open pools of water for as long as 5 years and then
eventually sealing the waste in steel and concrete casks
• In CA, waste is stored near earthquake faults, and most
other plants are located near major water sources, due to
the large amount of water that is required for keeping the
reactor cores cool
• Many feel that it is dangerous to leave the waste ________
_______________ (i.e. it is vulnerable to terrorist attacks,
accidents, or natural disasters)
Long-Term Storage of Waste: Yucca Mt. Controversy
Yucca Mountain National Nuclear
Repository:
• 100 miles NW of Las Vegas on
western edge of the Nevada
Test Site
• Repository would be 1000 ft
below the top of the mountain
and 1000 ft above the ground
water.
Yucca Mountain
• $10 billion has
been spent so far
to build a 5 mile
long tunnel in the
mountain
Yucca Mountain
• 90% of waste from power
plants, 10% from defense
programs
• Waste is currently stored at
facilities in 43 states
Yucca Mountain Lawsuits
• There were many law suits against
Yucca Mountain project. Most cases
were dismissed except for the EPA
lawsuit on the following grounds:
• EPA was required to keep radiation
exposure to safe levels for as long as
National Academy of Sciences’
scientists determined the site would
have unsafe levels of radioactivity
• Scientists determined the site would
be highly radioactive for at least
100,000 years
• EPA would only guarantee site for
10,000 years, and argued that
nothing could be guaranteed for
longer periods.
Yucca Mountain
• In Sept., 2009, the Obama
administration withdrew its application to
have the facility licensed in a way that
would prevent the Yucca Mountain
project from being revived in the future
• _____________________________
________________________________
________________________________
_______________________________.
• The energy utilities want their money
that they paid to build Yucca Mountain
back.
Nuclear Energy
Pros:
• U.S. has major reserves of uranium;
• lower mining impacts than coal;
• ____________________________________
(none in nuclear reactor, some in production of fuel);
• no air pollution/acid-forming emissions;
Cons:
• high cost; some of cost subsidized by government (esp.
_________________________________)
• possible major release of radioactive contaminants;
• mining & processing impacts;
• storage of radioactive wastes;
• possible terrorist attacks
• thermal pollution- which ___________________________
Nuclear Fusion
nuclear fusion: a nuclear change in which two
isotopes of light elements are ______________
to form a heavier nucleus, releasing energy in
the process.
A nuclear fusion of
helium (He) formed
by fusion of two
hydrogen (H)
nuclei is the source
of energy of the
________.