RADIOACTIVE DATING
A helpful application of radioactive decay is in the determination of the ages of
substances such as rocks and relics that have bits of organic material trapped in
them. Because carbon-14 has a half-life of about 5,700 years and occurs in the
remains of organic materials, it has been useful in dating these materials. A small
percentage of CO 2 in the atmosphere contains carbon-14. The stable isotope of
carbon is carbon-12. Carbon-14 is a beta emitter and decays to form nitrogen-14:
In any living organism, the ratio of carbon-14 to carbon-12 is the same as in
the atmosphere because of the constant interchange of materials between organism
and surroundings. When an organism dies, this interaction stops, and the carbon-
14 gradually decays to nitrogen. By comparing the relative amounts of carbon-14
and carbon-12 in the remains, the age of the organism can be established. Carbon-
14 has a half-life of 5,700 years. If a sample of wood had originally contained 5
grams of carbon-14 and now had only half or 2.5 grams of carbon-14, its age
would be 5,700 years. In other words, the old wood emits half as much beta
radiation per gram of carbon as that emitted by living plant tissues. This method
was used to determine the age of the Dead Sea Scrolls (about 1,900 years) and
has been found to be in agreement with several other dating techniques.
NUCLEAR REACTIONS
Nuclear fission reactions have been in use since the 1940s. The first atomic
bombs used in 1945 were nuclear fission bombs. Since that time, many countries,
including our own, have put nuclear fission power plants into use to provide a
new energy source for electrical energy. Basically, a nuclear fission reaction is
the splitting of a heavy nucleus into two or more lighter nuclei.
EXAMPLE:
U-235 is bombarded with slow neutrons to produce Ba-139, Kr-94, or other
isotopes and also 3 fast-moving neutrons.
A nuclear chain reaction is a reaction in which an initial step, such as the reaction
above, leads to a succession of repeating steps that continues indefinitely. Nuclear
chain reactions are used in nuclear reactors and nuclear bombs.
A nuclear fusion reaction is the combination of very light nuclei to make a
heavier nucleus. Extremely high temperatures and pressures are required in order
to overcome the repulsive forces of the two nuclei. Fusion has been achieved only