Development of a large-area phoswich detector for simultaneous counting of alpha and beta rays at radioactively contaminated sites

Abstract

For radiological characterization, direct measurements and surface scans with a movable instrument can be performed to rapidly determine contamination levels and identify hot spots. A movable instrument with an appropriate minimum detectable concentration (MDC) can yield reliable measurements for accurate analysis. In this study, large-area phosphor sandwich (phoswich) detectors for simultaneous alpha and beta detection were fabricated to investigate variations in MDC with probe area. Before fabricating phoswich detectors with probe dimensions of 10 × 10 cm, 15 × 15 cm, and 20 × 20 cm, Monte Carlo simulations were performed to optimize the detector components. The phoswich detectors were then fabricated based on the simulation results, and instrument calibration was performed using 10 × 10 cm $^{241}Am$, $^{90}Sr/Y$, $^{99}Tc$c, and $^{14}C$ radioactive sources. For increasing the precision of calibration, a source-area correction approach was proposed and applied by taking advantage of the symmetric probe geometry. The experimental outcomes of instrument efficiency and background count rate were employed in the MDC calculation. The results indicated that the static and scan MDCs for the 15 × 15 cm and 20 × 20 cm probes were superior to those for the 10 × 10 cm probe. However, the static MDC for the 15 × 15 cm probe was similar to that for the 20 × 20 cm probe, while the scan MDC for the 15 × 15 cm probe was mostly inferior to that for the 20 × 20 cm probe. Because the static MDCs for the 15 × 15 cm and 20 × 20 cm probes were not significantly different and can be reduced by extending the measurement period, the 20 × 20 cm probe seems to be more effective than the 10 × 10 cm and 15 × 15 cm probes for rapidly covering a wide potentially contaminated site.