We have been talking about the activity of a radioactive material in terms of disintegration of the atoms in the material and not about the resulting radiation. This leads us to another distinction among radioactive materials. That is, one disintegration in a radioactive source does not necessarily result in the same amount of radiation emission.

Let's look at an example

In a Cobalt-60 source (Co-60) each atom decays by emitting a beta particle. Almost immediately additional energy adjustments are made in the atom and two gamma rays are emitted. Each of the gamma rays possess a certain energy level that is always the same. Therefore, when a CO-60 source decays, each disintegration of an atom results in two gamma rays. Another example of characteristic decay patterns is that of Thulium-170 (Tm-170). When TM-170 decays, approximately ¼ of its atoms emit beta particles and an associated gamma ray. The other ¾ of the atoms are beta emitters with no associated gamma emission. This decay pattern is always the same for TM-170. The point here is that even though the activities of different isotopes may be the same, the number of gamma rays resulting from decay of their atoms can be different.


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