Nuclear Medicine Blog

Nuke-Tek by Ann Marie Alessi

Exposure Filters on a Geiger-Müller (GM) Counters for Alpha Particles

January 23, 2013
Ann Marie Alessi, BS, CNMT, NCT, RT(N), FSNMMI-TS, Product Sales Manager, Nuclear Medicine, Biodex Medical Systems, Inc.

Nuclear Catalog #119The survey meter is an essential resource a technologist has to determine the presence of radiation contamination in typical surveys such as during routine area surveys, checking incoming packages, testing after spills or other radiation incidents and measurement of waste held for decay-in-storage prior to disposal.  A literature review of incident and overexposure reports indicate that a majority of these events occurred because a radiation worker did not have or did not use a survey meter. With the development of new radiotracers for therapy using alpha and beta emitters, it is important that the proper equipment is used to survey for contamination.

     As you may know, a GM pancake probe detector has a significant overresponse at lower energies between approximately 20 to 160 keV seen with alpha particle emitters (see red line on graph below).  Any exposure or dose measurements taken with an unfiltered GM pancake detector would thus have unacceptable errors at these lower energies. Using this filter while surveying for contamination from alpha particles, flattens the energy response to within ± 20% referenced to 137Cs (662 keV) over an energy range of 33 keV to 1.2 MeV.  >>



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