Answer to Question #4510 Submitted to "Ask the Experts"

Regarding the emission strength of beta radiation, how would you describe a "weak" emitter, a "soft" emitter, and a "pure" emitter? I am researching information about tritium and promethium-147. I have read that tritium is a "weak" emitter and promethium is a "soft" emitter.

In reference to beta-emitting radionuclides, the terms "weak" and "soft" are often used interchangeably. Both are intended to convey the fact that the energies of the beta particles emitted by the radionuclide of interest are low in energy. What constitutes low energy is somewhat subjective, depending on the observer’s own interests and perspective, but most people concerned with beta radiation would likely agree that a radionuclide that emitted beta radiation with a maximum beta energy less than a few hundred keV could be characterized as a low-energy beta-emitter, or as a "weak" or "soft" beta-emitter. While some individual authors may attempt to distinguish low-energy beta-emitters, such as tritium or nickel-63, from other somewhat higher energy emitters, such as promethium-147, through the use of words such as "weak" and "soft," I am aware of no formal distinction in the use of these words for such a purpose. The reference to a "pure" beta-emitter, refers to the fact that the radionuclide of interest emits no radiations other than beta particles during its decay.

George Chabot, PhD, CHP