Relationship between Induced Indium Activity and Count Rates of Survey Meters Used to Screen Personnel Exposed in Criticality Accidents

*Small pieces of indium foil have been universally adopted by many nuclear facilities for the purpose of screening personnel exposed in criticality accidents because any neutron-induced activity of indium foil can be measured with survey meters. The authors performed experiments in which the counting efficiency of a survey meter to radiation from activated indium foil was evaluated using a 252 Cf neutron source. In those experiments pieces of indium foil were irradiated outside an aluminum tube containing a 252 Cf source, all of which was placed inside an annular PMMA cylinder moderator. The count rates to indium activity were then measured with a portable GM survey meter. Reference values of the activity of 115m In and 116m In were evaluated using measurements with a germanium detector and MCNP-4C2 calculations, resulting in the counting efficiency of a survey meter being evaluated to be 0.6 %. This result then allowed appropriate doses to be converted from the count rates to be applied in the screening procedure.