Measurement of gamma ray dose from a moderated 252Cf source

The fraction of dose equivalent due to gamma rays from a moderated 252Cf source was determined using three types of dosimetry system. Two A-150 tissue-equivalent (TE) plastic ionisation chambers and a TE proportional counter (TEPC) were used to measure tissue dose, from which the neutron dose equivalent was computed. The ratio of gamma ray dose equivalent to the neutron dose equivalent was determined by using a relatively neutron insensitive Geiger-Mueller (GM) counter and thermoluminescence dosemeters (TLD). In addition, the event-size spectrum measured by the TEPC was also used to compute the gamma ray dose fraction. The average value of the ratio of gamma ray dose to neutron dose equivalent was found to be 0.18 with an uncertainty of about +- 18%. (author)