Radioactivity
Not all Isotopes are stable. Isotopes with atomic numbers
greater than 92 are unstable. Americium used for moisture
measurement in the nuclear gauge has an atomic number of
95. It is a by-product from neutron bombardment of Plutonium
to produce weapons materials. All 13 isotopes of Americium
that have been identified are radioactive.
Some isotopes of lower atomic number are also unstable;
Cesium-137 used in the nuclear gauge for density
measurement has an atomic number of 55. Of 22 isotopes
identified, Cesium-133 found in nature is stable, while Cesium-
137, a by-product of making atomic weapons materials, is not.
By nuclear reactions, man has produced a large number of
unstable isotopes not found in nature.
Any unstable isotope that gives off energy—while decaying to
a stable isotope—is defined radioactive. Like other forms of
energy, radiation can be useful or harmful depending upon its
use.
Alpha, Beta, Neutron, and Gamma Radiation
Sources used in the nuclear gauge are composed of four types
of radiation: Alpha particle, Beta particle, Photons (gamma
rays), and Neutrons.
Alpha Particles travel only about an inch in air and are stopped
by a sheet of paper or the skin tissue. In the nuclear gauge,
alpha particles are used to produce neutrons.
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