Feasibility Assessment of a Phoswich Detector for Simultaneous Measurement of a Mixture of Beta-and Gamma-Emitters

The decommissioned nuclear site could be released from regulatory control only if the residual radioactivity is confirmed to be lower than the release criteria. For this, the radioactive nuclides remained in soil shall be identified and evaluated considering the radiation exposure pathways. Most of remaining in soil nuclides are gamma emitter, some nuclides are beta-emitter or gamma-beta emitter. The samples collected from soil at the decommissioned nuclear are usually mixture of gamma-and beta-emitters. To identify the radionuclide in the samples, it is needed to detect simultaneously beta and gamma radiation. At present, however, the separate measurements for beta and gamma radiation by using different detectors are needed. This paper applied the phoswich detector, which is a kind of fiber-optic radiation sensor (FORS), to simultaneous detection of beta-and gamma-radiation. Then, its detection efficiency are evaluated. The two types of FORS sensing probe were fabricated by using a bundle of the organic plastic scintillator (BCF-12) and inorganic scintillator, (Lu, Y)
₂
SiO
₅
:Ce (LYSO:Ce). The detection efficiencies by the FORSs were evaluated by comparing counts by using a commercial detector against the disk type radiation source of Sr-90, Cs-137, individually or simultaneously. The comparison showed that the FORS developed in this study has efficiency and capability enough to measure beta and gamma radiation distinguishable from the background radioactivity.