Model 3440-L B–3
B. RADIATION THEORY
RADIATION THEORY
Radioactivity is the spontaneous breakdown of unstable nuclei
(radioisotopes) with the resulting emission of radiation. The basic unit of
radiation used in the U.S.A. is the curie (Ci). The curie is defined as 3.7 x
10
10
disintegrations of nuclei per second. In the “Special Form”
encapsulated sealed sources used in the 3440-L gauge, the unit of measure
is the millicurie (1/1,000 of a curie). The SI unit of radiation is the
becquerel (Bq). The becquerel equals one disintegration per second.
Therefore, one curie equals 3.7 x 10
10
becquerel.
The strength of radioactive material is measured by its activity, or rate of
decay. This activity decreases with time. The length of time it takes a given
amount of radioactive material to decay to half of its original strength is
referred to as the half-life. The Am-241:Be source in the Model 3440-L has
a half-life of 432 years, while the half-life of the Cs-137 source is thirty
years.
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