Helical gamma scanning technique for activity detection of radioactive waste drum

[Background] Non-destructive assay (NDA) is a widely used method to assay the amount and categories of radioactive nuclides within the waste drum, segmented gamma scanning (SGS) is a normal method. [Purpose] This study aims to evaluate the performance of helical gamma scanning (HGS) for 400-liter waste drum. [Methods] Based on SGS, a new HGS detection method was proposed. The scanning mode and reconstruction algorithm were improved in SGS to realize continuous scanning measurement. Monte-Carlo method was employed to simulate the reconstruction process of three nuclides in a 400-liter waste drum filled with three different density media. Results of three point sources and three homogeneous medium materials were compared. [Results] At low density, the root mean square error of SGS is more than 8%, while that of HGS is less than 6.5%. At medium density, the reconstruction error of SGS is more than -55%, which seriously underestimates the risk of waste drum. Compared with SGS, HGS saves at least half of the measurement time. [Conclusions] HGS technology is suitable for measuring 400-liter waste drum whose density is low and medium. The measurement time of HGS is less than SGS and tomographic gamma scanning (TGS). The measurement accuracy of HGS is better than SGS. (authors)