Environmental Science
Introduction to Nuclear Energy
Lecture Notes
Nuclear energy = the energy
trapped inside an atom
• Nuclear energy was first
introduced in 1945, when
two fission bombs were
used against Japan
Little Boy
Fat Man
QUICK REVIEW
ATOMSNUCLEUSPROTONSNEUTRONSELECTRONSELEMENTS
• In most atoms . . .
# Protons = # Neutrons
• Atomic Number =
• Atomic Mass =
*Atomic (Proton) Number vs. *Atomic Mass vs. *Neutron Number
ISOTOPES
• ISOTOPES=
• EXAMPLE:
• Carbon-12 and Carbon-16
• How many protons and neutrons would each atom
contain?
Isotopes Video
Comprehension Check
• Circle each atom at right
that would be an isotope
of the atom below. Look
on the period table, what
element does the atom
below represent?
• Most isotopes of atoms are stable, but, sometimes this is
not the case:
– Radium-226 (the name of the atom is radium, its atomic mass is
226)
• RADIOACTIVITY: the nucleus of Radium-226 is unstable
and breaks down and release energy and atomic subparticles. The release of these particles is
radioactivity.
• When a radium atom breaks down (decays), a sub-atomic
particle flies out of the nucleus at a high speed. This
releases energy.
• Isotopes try to decay to more stable isotopes.
When They Decay, Atoms Emit
One of the Following:
1. Alpha Particles: equivalent to 2 protons + 2
neutrons (He-4 nucleus)
• They travel only a few inches through air and can
easily be stopped with a sheet of paper.
Radioactive Decay Video
2. Beta Particles: electrons
• Beta particles can
travel a few feet
through air and can be
stopped with a few
sheets of aluminum
foil.
3. Gamma Rays: high frequency
photons (electromagnetic wave)
• Gamma radiation is able to
travel many meters in air
and many centimeters in
human tissue. It readily
penetrates most materials
and is sometimes called
"penetrating radiation."
• The half-life of an
isotope is the amount of
time it takes for half of
the atoms to decay into
a more stable form.
• Naturally abundant
isotopes exist around us
because their half-lives
are longer than the age
of the earth.
Calculating Half Life Problems
EXAMPLES:
• Uranium 238 (238U) has a half-life of 4.5
billion years so it is naturally abundant.
• Most isotopes have short half-lives and
must be produced in the laboratory to
study or use.
• Cobalt-60 (Co-60) has a half-life of 5.3
years and is made in a reactor. Co-60 is
used for radiation therapy of cancer
patients.
PROBLEMS
1. How can you tell if you have an isotope?
– See Periodic Table of Elements
– Check Atomic Mass
– If different than Periodic Table, you have an
isotope
•
EXAMPLE: Is Calcium-35 an isotope? If
so, of what atom is it an isotope?
2. How many protons and neutrons does
Calcium-35 contain?
– See Periodic Table of Elements
– Check Atomic Number
– Subtract Atomic Number from Atomic Mass
3. An isotope of cesium (cesium-137) has a
half-life of 30 years. If 1.0 mg of cesium137 decays over a period of 90 years, how
many mg of cesium-137 would remain?