Measuring and Predicting Gamma Radiation from Radioactive Glass-Filled Canisters

Measurement and prediction of outside surface exposure rates and measurement of gamma photon spectra from radioactive sources are described. The sources were 30-cm-diam canisters filled with borosilicate glass to a height of ∼100 cm. Each canister contained up to 237 kCi of ¹³⁷ Cs and 159 kCi of ⁹⁰Sr. Exposure rates on the outside surfaces ranged from 26 000 to 320 000 R/h, chiefly from decay of ¹³⁷ Cs. The radiation field around the canisters was modeled using two codes based on point kernel theory (ISOSHLD-II and QAD-CG) and a transport theory code (ANISN). It was found that the point kernel codes overpredicted surface exposure rates for the radioactive canisters by a factor of ∼2. The surface exposure rates calculated by the transport theory code were ∼25% higher than the measurements. Spectral measurements indicate that most exposure is associated with gamma radiation in the 0.1- to 0.5-MeV range.