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Nuclear Equations
In nuclear equations, we balance
nucleons (protons and neutrons). The
atomic number (number of protons) and
the mass number (number of nucleons)
are conserved during the reaction.
Nuclear Equations
Alpha Decay
Nuclear Equations
Beta Decay
Nuclear Equations
Beta Decay
Nuclear Equations
Positron Emission: A positron is a particle
equal in mass to an electron but with opposite
charge.
Nuclear Equations
Electron Capture: A nucleus absorbs an
electron from the inner shell.
Nuclear Equations
EXAMPLE 4.1 Balancing Nuclear Equations
Write balanced nuclear equations for each of the
following processes. In each case, indicate what new
element is formed.
a. Plutonium-239 emits an alpha particle when it
decays.
b. Protactinium-234 undergoes beta decay.
c. Carbon-11 emits a positron when it decays.
d. Carbon-11 undergoes electron capture.
Write balanced nuclear equations for each of the
following processes. In each case, indicate what new
element is formed.
a. Radium-226 decays by alpha emission.
b. Sodium-24 undergoes beta decay.
c. Gold-188 decays by positron emission.
d. Argon-37 undergoes electron capture.
Exercise 4.1
EXAMPLE 4.1 Balancing Nuclear Equations continued
In the upper atmosphere, a nitrogen-14 nucleus absorbs
a neutron. A carbon-14 nucleus and another particle are
formed. What is the other particle?
EXAMPLE 4.2
5
More Nuclear Equations
Half-Life
Half-life of a radioactive sample is the
time required for ½ of the material to
undergo radioactive decay.
Half-Life
Half-Life
Fraction Remaining = 1/2n
Half-life
T1/2 = 0.693/ k(decay constant)
If you know how much you started with and
how much you ended with, then you can
determine the number of half-lives.
If you also know the start and end time, you
can divide the time by the number of half-
lives to give you the T1/2.
Half-life
To determine starting amounts or ending
amounts:
ln(Nt/No) = -kt
Nt is the number of radioactive nuclei at your
ending
No is the number of radioactive nuclei at the
start
K is the decay constant
Radioisotopic Dating
Radioisotopic Dating
Carbon-14 Dating: The half-life of
carbon-14 is 5730 years. Carbon-14 is
formed in the upper atmosphere by the
bombardment of ordinary nitrogen atoms
by neutrons from cosmic rays.
Radioisotopic Dating
Tritium Dating: Tritium is a radioactive
isotope of hydrogen. It has a half-life of
12.26 years and can be used for dating
objects up to 100 years old.
Nuclear Chain Reaction
Fission of one
nucleus produces
neutrons that can
cause the fission of
other nuclei, thus
setting off a chain
reaction.
Manhattan Project
The Manhattan Project was launched by
President Roosevelt in 1939. It consisted
of 4 separate research teams attempting
to:
a. Sustain the nuclear fission reaction.
b. Enrich uranium.
c. Make fissionable plutonium-239.
d. Construct a fission atomic bomb.
Manhattan Project
Replicas of “Little Boy”
(dropped on Hiroshima)
and “Fat Man”
(dropped on Nagasaki).
Manhattan Project
Mushroom cloud over
Nagasaki from the
detonation of “Fat
Man,” August 9, 1945.
Radioactive Fallout
Many radioactive isotopes are produced in a nuclear
bomb blast. Some are particularly harmful to humans.
Among these are strontium-90 and iodine-131.
Strontium-90: Half-life = 28.5 years, chemically similar to
calcium. Obtained from dairy and vegetable products
and accumulates in bone.
Iodine-131: Half-life = 8 days. Concentrates in the thyroid
glands.
Nuclear Power Plants
Civilian nuclear power plants use less
enriched uranium (2.5-3.5% uranium-235
rather than 90% for weapons-grade).
The nuclear chain reaction is controlled
for the slow release of heat energy. The
heat is used to make steam, which turns a
turbine to produce electricity.
The Nuclear Age