Download Review of Nuclear Chemistry

Review of Nuclear Chemistry:
This is not a complete list, only an outline. Review your notes, study sheet #5, text (Chapt. 6, pp. 465-471 & pp.
606-613) and quizzes for a more compete summary.
Notation:
Example:
Roetgen 1895 (pronounced Rentkin) discovers X-rays.
Soon after Becquerel discovers U spontaneously emits radiation.
Marie & Pierre Curie study radioactivity materials.
Marie Curie coins the term "radioactivity;" also she isolates Po and Ra.
Memorize:
Table 1
Symbol
Particle Name
Charge
Mass
(amu)
alpha
2
4
beta
-1
0
gamma
0
0
You should know how penetrating and the relative speeds of the particles in Table 1.
An alpha particle is the largest radiation particle; while a gamma particle is the fastest.
A gamma particle is the most dangerous form of radiation outside the body, while an alpha particle is the most
dangerous inside the body.
During an alpha decay, a radioactive element's mass number decreases by 4 while its atomic number decreases by 2.
During a beta decay, a radioactive element's mass number does not change while the number of protons increases by
one. This is because beta particles are thought to form when a neutron becomes a proton in the nucleus.
You should know how to balance a nuclear reaction.
When an element under goes decay of a particle listed in Table 1. The original element is listed as a reactant and the
particles and resulting element(s) is (are) listed as products.
Examples:
Plutonium-239 undergoes alpha decay:
Tritium undergoes beta decay:
.
There are two types of decay series natural and artificial.
There are 3 natural decay series:
.
The double arrow means that more than reaction/decay occurs before the final product is produced. Note all three
reactions begin with species found in nature and end with isotopes of lead. If you can determine which isotope is
formed, you can determine the starting material.
In nature uranium-238 is much more common (99.3%) than uranium-235 (0.7%).
Uranium-235, unlike uranium-238, can undergo a sustained chain reaction. Because it can do this we call uranium235 fissionable.
Carbon dating:
Carbon dating can be used to determine the age of objects (usually greater than 1000 years old) that contain carbon.
The way it works is that living organic matter contains a ratio of carbon-14 to carbon-12 (1: 1 x 1012). Carbon-14
undergoes beta decay:
to give nitrogen. So over time carbon-14 becomes nitrogen. The half-life of carbon-14 is 5730 years. A new element
that contains carbon gives off more beta counts per hour than an older object, because the older object is depleted of
carbon. The formula to calculate the fraction of carbon-14 remaining is:
F = Fraction of carbon-14 remaining = Error!
=,
where n = the number of half-lives (note: n is not the half-life of the element!).
If you know the number of beta counts from the new and old objects, you can calculate the number of half-lives.
From the number of half-lives you can calculate the age of the object. Remember as an object ages it gives off fewer
beta particles (see above).
If you know the number of half-lives that have passed, you can calculate the fraction of carbon-14 remaining.
Also note: this formula works for compounds other than carbon-14, but the length of the half-live will be
different for different elements.
Radiation Exposure
The majority of exposure to radiation comes from natural sources, such as radon (Rn), cosmic rays, food, rocks and
soils. The bulk of this natural radiation comes from radon gas. Radon gas is an alpha emitter, so the concern is that
we will breathe radon into our lungs, where it can cause harm. Radon is a uranium daughter, meaning that it is
formed by the natural decay of U-238.
On average, exposure from radiation from nuclear power plants and global nuclear fall out is small, when compared
to natural sources.
Radiation has been used effectively for medical treatment and diagnosis.
Living at altitude in Colorado, we are exposed to more radiation (via cosmic rays) than people living a sea level.
FISSION
In 1934 E. Fermi bombards U-238 to make plutonium.
In 1938 Hahn & Strassman repeat Fermi's experiment, but use U-235 and obtain new products and lots of neutrons.
They call this process "nuclear fission." The multiple neutrons produced can sustain a chain reaction if a critical
mass of U-235 is present.
The change in mass = 0.184 amu. This mass is changed into energy. In fission (and in fusion) reactions, matter (or
mass) is changed to energy:  E =  m c2 , where E is energy, m is mass, and c is the speed of light.
It did not take long for scientists to realize that a fission reaction could be used in a nuclear bomb, but there were
huge engineering problems to overcome.
To address these problems, the Manhattan Project in 1942 was established. U-235 and plutonium were needed to
make nuclear bombs. Uranium has to be enriched (converted from U-238 to U-235) to 90% to make a bomb. Any
type of plutonium is weapons grade.
Nuclear power plants
"Controlled fission"
Nuclear power plants use fuel rods containing 3% U-235. These fuel rods have a life of about 3 years. A core of a
nuclear power plant is composed of several hundreds of these rods. To control the heat generated by the fission
reaction in the fuel rods, control rods (which absorb neutrons, and thus slow the speed of the chain reaction) can be
moved in or out of the reactor.
Idea: fission reactions make heat, the heat boils water, which turns a turbine, which powers a generator, and then the
energy is put on the grid.
There are about 100 nuclear reactors in the US. On average, a nuclear power plant has a lifetime of about 30 years.
The world's supply of U-235 is diminishing and for this reason, there is an interest in Breeder Reactors.
Nuclear Power Plant Accidents
1979: Three-Mile Island (TMI), near Harrisburg, PA
The core of unit 2 lost cooling water due to confusion in the control room. This confusion was due to conflicting
signals and poor training of the technicians. The temperature in the core reached 2000 C. The core was heavily
damaged due to this release of heat, but a much more serious disaster was averted because the containment building
held. Because the containment building did not melt, there was not a major release of radioactive species. There was
a release of some radioactive noble gases. Unit 1 at TMI is still operating.
1986: Chernobyl, Ukraine
Problem: the Soviet RBMK design of nuclear power plants is unstable at low power and they lack an adequate
containment building.
A test of the plant was conducted to see how the reactor performed at low power (30 % of total power). The reactor
power dropped to 1%. In order to continue with the test an operator at the plant shut off the emergency shut down
procedure, removed all by 6 control rods (by remote control) and tried to control the temperature in the core by
manually controlling the flow of cooling water.
These factors led to the MELTDOWN:
Tcore > 3000  C
Building melted.
Lid was blown off the reactor core, and then there was an explosion of hydrogen gas.
The radioactive dust in the sarcophagus remains a potential problem and has implications for those living far beyond
the Ukrainian boarder.
FUSION:
The combining of two small nuclei to make one new nucleus.
Fusion is what powers our sun!
In fission reactions the nucleus was split apart, in fusion nuclei come together.
More energy per unit mass is created.
Ex.
Mass: H = 1.0073 amu, n = 1.0087 amu , He= 4.0015 amu ,  mass = 0.0305 amu .
Questions you should be able to answer:
What is a radioisotope?
What is radiation?
What is a transuranic element? Who was the first to make such an element? How did he do it?
What is ionizing radiation?
What are some common sources of radiation that one can be exposed to on a yearly basis?
During the cold war, what was the role of the plants at Oak Ridge, Tennessee; Hanford, WA; Los Alamos, NM; and
Rocky Flats, CO?
How does the enriching process for uranium work? What technique is used? What is the starting material and what
is achieved in the process?
What are the aftereffects of Chernobyl?
What are some of the benefits of nuclear chemistry and what are some of the drawbacks?
How do breeder reactors work? Why are they cooled with liquid sodium? Why are they popular is some countries
and not others? Why do peace groups oppose them?
What is the difference between fission and fusion?
What is an atomic bomb (A-bomb) and how does it differ from a hydrogen (H-bomb)? Which is more powerful?
What is the bonding energy of the nucleus?
What is the difference between high level and low level waste?
What does it mean if waste is vitrified? When is this done and why? (See p. 609 of your text)
What is type of wastes are scheduled to be shipped to WIPP? Yucca Mountain?
You should also be prepared to answer questions about Rocky Flats and what would happen during a "nuclear
winter."