Passive Gamma Ray Measurements for a Simple Determination of Radioactivity of Uranium in Waste Drums

Abstract

Intending to apply to radioactive waste drums for trench disposal, we have developed a new analysis method on measuring radioactivity of uranium filled in waste drums using passive γ ray measurement. We proposed a new evaluation function which gives a unique relation between source positions and γ ray count rate. This evaluation function was derived from the measurement method using two opposite detectors. The new evaluation function is given by 1/{ln(k/R(1))×ln(k/R(2))}, where “R(1)” and “R(2)”) are the ratios of two γ ray (766keV and 1001keV) count rates measured by the detectors. These γ rays are emitted by ^234mPa (²³⁸U daughter). “k”) is the ratio of emission rates of the two γ rays. We discovered that the evaluation function uniquely relates between 1/{ln(k/R(1))×ln(k/R(2))} and (n₁×n₂)^1/2, where “n₁” and “n₂” are the γ ray count rates measured by the detectors. We examined the relation between1/{ln(k/R(1))×ln(k/R(2))} and (n₁×n₂)^1/2 by simulation and measurement of uranium sources using two opposite detectors. The uranium sources are set in the drum in several positions. The linearity between 1/{ln(k/R(1))×ln(k/R(2))} and (n₁×n₂)^1/2 was shown by the simulation. The measurement data corresponds with the linearity with 5 percent or less of error.