Background Radiation
• 3/4ths of all exposure to radiation comes
from background radiation.
• Most of the remaining ¼ comes from
medical irradiation such as X-rays.
Radiation and Cells
• Radiation is capable of removing electrons
from cells, forming ions; hence the term
ionizing radiation.
• Molecules can also splinter into neutral
fragments called free radicals. Free
radicals can disrupt cellular processes.
Radiation and Cells
• Radiation often affects the fastest growing
cells and tissues such as white blood
cells and bone marrow.
• Ionizing radiation call also disrupt DNA,
causing mutations.
Radiation Damage to Cells
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
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
Nuclear Equations
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.
EXAMPLE 4.1
Balancing Nuclear Equations continued
Exercise 4.1
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.
EXAMPLE 4.2
5
More Nuclear Equations
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?
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
Work examples from hand out
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.
Artificial Transmutation
Bombardment of stable nuclei with alpha
particles, neutrons, or other sub-atomic
particles cause new elements to form.
This process is known as artificial
transmutation.
Uses of Radioisotopes
Tracers: Radioisotopes can be easily
detected through their decay products.
Therefore they can be used to trace their
movement.
– Detect leaks in underground pipes.
– Determine frictional wear in piston rings.
– Determine uptake of phosphorus and its
distribution in plants.
Uses of Radioisotopes
Irradiation of Food: Radioisotopes can destroy
microorganisms that cause food spoilage.
Nuclear Medicine
• Radiation Therapy: Nuclear radiation
can be used to kill cancerous cells.
Radiation is most lethal to fastest growing
cells. Radiation is aimed at the cancerous
tissue. Patients undergoing radiation
therapy often experience nausea and
vomiting, which are early signs of radiation
sickness.
Nuclear Medicine
Diagnostic Uses of Radiation
Nuclear Medicine
• Gamma Ray Imaging or Positron:
Technetium-99m emits gamma radiation. It can
be used to image the heart and other organs
and tissues.
Nuclear Medicine
• Positron Emission Tomography (PET): A patient
inhales or is injected with positron-emitting isotopes such
as carbon-11 or oxygen-15. When positrons encounter
electrons, they emit two gamma rays, which exit the
body in opposite directions. PET scans can be used to
image dynamic processes.
Penetrating Power of Radiation
• Alpha radiation is least penetrating and can
penetrate the outer layer of skin. Alpha radiation
is stopped by a sheet of paper.
• Beta radiation can penetrate through a few cm
of skin and tissue. Beta radiation is stopped by
a sheet of aluminum foil.
• Gamma radiation will pass right through a
body. Gamma radiation requires several cm of
lead to stop.
Penetrating Power of Radiation
Penetrating Power of Radiation
Penetrating Power of Radiation
Two means of protecting oneself from radiation are
distance and shielding.
Distance: Move away from the source. The
intensity of radiation decreases with increasing
distance from the source.
Shielding: Lead is a commonly used shield for
radiation.
Talk about Radon
Energy from the Nucleus
When protons and
neutrons combine to
form a nucleus, a
small amount of mass
is converted into
energy. This is
known as binding
energy.
The Building of the Bomb
Nuclear Fission: Fission occurs when
larger nuclei split into small nuclei.
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.
b.
c.
d.
Sustain the nuclear fission reaction.
Enrich uranium.
Make fissionable plutonium-239.
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