Environmental ScienceIntroduction 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 ATOMSNUCLEUSPROTONSNEUTRONSELECTRONSELEMENTS

• 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 sub-particles. 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.

PROBLEMS1. 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 cesium-137 decays over a period of 90 years, how many mg of cesium-137 would remain?