Nuclear Chemistry
a.k.a. Radiation
AAAAHHHHH NOOOOO!
Duck and cover!
What do you know?
• All nuclear materials remain highly
toxic for thousands of years.
false -Some radioisotopes have-lives
of seconds or days, while others like
plutonium-239 has a half-life of 2.4 x
104 years.
What do you know?
• Man-made radiation is more toxic to
humans than naturally occurring
radiation even if the dose is the same.
false - The body makes no
distinction; it sees radiation as
deposited energy regardless of its
source.
What do you know?
• The human body has the capability to
repair damaged caused by exposure to
radiation.
true - Many of the DNA lesions induced by
ionizing radiation are similar to identical to
those induced as a consequence of normal
metabolic activity. DNA repair mechanisms
can act to reduce the consequences of this
damage.
What do you know?
• In the US, most cases of cancer in
humans are known to be caused by
man-made radiation.
false - Most cancers have an
unknown cause or etiology.
What do you know?
• I would rather live within a 50 mile
radius of a coal-burning plant than a
nuclear power plant.
false - Actually a coal burning plant
gives off slightly more radioactivity
due to the thorium and uranium
content in coal. But in both cases the
levels are extremely low.
What do you know?
• One of the chief dangers from nuclear
power plants is that they can explode
like a nuclear bomb.
false - There's a big difference between a
nuclear core and a nuclear bomb. After
detonation, the density of uranium (or
plutonium) atoms in a bomb is incredibly
high, enough for fissions to take place and
energy to be released in a hundred
millionth of a second! So it flies apart. The
density of atoms in a nuclear core is much
less, and, even in a meltdown situation
would generate heat at a much slower rate
than is necessary to fly apart. The act of
meltdown actually terminates the explosive
process, because when a core "melts
down" it spreads out and goes sub-critical.
What do you know?
• It is safer to drive behind a tanker truck
carrying gasoline than a truck load of
spent nuclear fuel.
false - People occasionally die in
gasoline truck accidents, but the DOE
and the nuclear industry claim that no
one has died or been hurt by a
radiation release due to a nuclear
waste transportation accident.
What do you know?
• On average, people are exposed to
more radiation from nuclear power
plants than from radon gas in homes.
false - An individual gets about 200
millirems of radiation per year from
naturally occurring radon. A normally
functioning nuclear power plant
exposes a person to about.01
millirem, if the person lives within 50
miles of the plant.
What do you know?
• Since the construction of the first
nuclear power plant, man-made
radiation in known to have resulted in
new species of plants and animals.
false - New species don't occur any
more frequently today than before
nuclear plants were built.
What do you know?
• The fact that nuclear power plants have
elaborate evacuation plans for the
surrounding area indicates they are
inherently more dangerous than other
types of plants.
What do you know?
false - Evacuation plans have only been
around since 1980 and are an example of
"regulatory ratcheting" by the Nuclear
Regulatory Commission. Other countries
do not have these plans. Chemical plants
do not have evacuation plans even though
evacuations in their vicinity are more likely
to be necessary than around a nuclear
power plant. Most evacuations are due to
rail or truck accidents involving toxic
chemicals.
The Nucleus
• Remember that the nucleus is comprised of
the two nucleons, protons and neutrons.
• The number of protons is the atomic number.
• The number of protons and neutrons together
is effectively the mass of the atom.
Isotopes
• Not all atoms of the same element have
the same mass due to different
numbers of neutrons in those atoms.
• There are three naturally occurring
isotopes of uranium:
Uranium-234
Uranium-235
Uranium-238
Radioactivity
• It is not uncommon for some nuclides of
an element to be unstable, or
radioactive.
• We refer to these as radionuclides.
• There are several ways radionuclides
can decay into a different nuclide.
Types of Radioactive Decay
Alpha Decay
Loss of an -particle (a helium nucleus)
4
2
238
92
U

He
234
90
4
2
Th+ He
Types of Radioactive Decay
Beta Decay
Loss of a -particle (a high energy electron)
0
−1
131
53
I

0
or −1
131

54
e
Xe
+
0
−1
e
Types of Radioactive Decay
Positron Emission
Loss of a positron (a particle that has the
same mass as but opposite charge than
an electron)
0
1
11
6
C
e
11

5
B
+
0
1
e
Types of Radioactive Decay
Gamma Emission
Loss of a -ray (high-energy radiation that
almost always accompanies the loss of a
nuclear particle)
0
0

Page 4
• Homework Read Page 5 and answer
page 6 in packet.
Stable Nuclei
• There are no stable nuclei with an
atomic number greater than 83.
• These nuclei tend to decay by alpha
emission.
Radioactive Series
• Large radioactive
nuclei cannot stabilize
by undergoing only
one nuclear
transformation.
• They undergo a series
of decays until they
form a stable nuclide
(often a nuclide of
lead).
Nuclear Fission
• How does one tap all that energy?
• Nuclear fission is the type of reaction carried
out in nuclear reactors.
Nuclear Fission
• Bombardment of the radioactive nuclide with
a neutron starts the process.
• Neutrons released in the transmutation strike
other nuclei, causing their decay and the
production of more neutrons.
• This process continues in what we call a
nuclear chain reaction.
Nuclear Fission
• If there are not enough radioactive nuclides in the
path of the ejected neutrons, the chain reaction
will die out.
• Therefore, there must be a certain minimum
amount of fissionable material present for the
chain reaction to be sustained: Critical Mass.
Nuclear Reactors
In nuclear reactors the heat generated by the
reaction is used to produce steam that turns a
turbine connected to a generator.
Nuclear Reactors
• The reaction is kept in
check by the use of
control rods.
• These block the paths of
some neutrons, keeping
the system from reaching
a dangerous supercritical
mass.
Nuclear Fusion
• Fusion would be a superior
method of generating power.
 The good news is that the
products of the reaction are
not radioactive.
 The bad news is that in order to achieve fusion, the
material must be in the plasma state at several million
kelvins.
 Tokamak apparati like the one shown at the right show
promise for carrying out these reactions.
 They use magnetic fields to heat the material.
Nuclear Transformations
Nuclear transformations can be
induced by accelerating a particle
and colliding it with the nuclide.
These particle accelerators are enormous, having
circular tracks with radii that are miles long.
Page 8 & Page 10
Nuclear Equations
• Page 16
• Just like a math
equation.
• Both sides must
equal.
Half Life
(no,not middle age)
Read Page 17
The half-life of a radioactive nuclide
is the amount of time it takes for
half of that nuclide to decay into a
stable nuclide.
The half-life of Carbon-14 is 5730 years
•After 5730 years, ½ the mass of an original
sample of Carbon-14 remains unchanged.
•After another 5730 years, ¼ (half of the half) of
an original sample of Carbon-14 remains
unchanged.
•The half-life of a radioactive nuclide cannot be
changed.
Regents Question:
As a sample of the radioactive isotope 131I decays,
its half-life
(1) decreases
(2) increases
(3) remains the same
How to determine how much of a
radioactive isotopes remains
unchanged after a period of time.
• Determine how many half-lives have
gone by (Time/half-life)
• Halve the mass of the starting material
for each half-life period that goes by.
How much of a 20.g sample of 131I remains
unchanged after 24 days?
The half-life period is 8 days so 24 days is
3 half-lives. Half the mass three times.
20.g
10.g
8 days
5.0g
8 days
2.5g
8 days
Regents Question:
Exactly how much time must elapse before 16
grams of potassium-42 decays, leaving 2 grams
of the original isotope?
(1) 8 x 12.4 hours
(2) 2 x 12.4 hours
(3) 3 x 12.4 hours
(4) 4 x 12.4 hours
16  8  4  2
Page18 . . .
Benefits of
Radioactive isotopes
• Tracers – are used to follow the course of
chemical (organic) or biological reactions
(C-14)
• Medical – isotopes (radioactive), with short
half-lives are quickly eliminated from body
 Technetium-99: pinpoints brain tumors
 Iodine-131: diagnosis and treatment of thyroid
disorders
 Radium and Cobalt-60: treatment of cancer
Benefits of
Radioactive isotopes
• Food can be stored longer because
radiation kills bacteria, yeast and molds
• Radioactive dating:
Geologic dating is based on half-life.
Uranium-238 occurs naturally in rock, it
decays to lead-206.
Dating living materials (organisms that
were previously alive). The ratio of C-14 to
C-12 can determine the age of a sample of
wood, bone, animal skin, or fabric.
Benefits of
Radioactive isotopes
• Nuclear Power – produce electricity
• Industrial Measurement – a beam of
subatomic particles (alpha, beta or
gamma) is blocked by a metal of a
certain thickness. Measuring the
fraction of the beam that is blocked
determines the thickness of the metal.
Risks of
Radioactive isotopes
• Biological Damage: exposure to
radiation can damage cells, or an
organism. When sex cells are
damaged, offspring may be affected.
• Long term storage: it is not known if
storing radioactive isotopes is safe.
• Accidents: cause fuel to escape
nuclear reactors (earthquake in Japan).