Development of a phoswich detector for low-energy gamma rays emitted from alpha emitters

Morishita, Yuki   ; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki  ; Sanada, Yukihisa   ; Torii, Tatsuo*  

The decommissioning of the Fukushima Daiichi Nuclear Power Station requires thorough inspection of piping for contamination, including alpha nuclides. Since external alpha particle measurements are impractical, detection relies on gamma-rays emitted by the alpha nuclides. Therefore, a phoswich detector for detecting low-energy gamma-rays was developed and experimentally validated. The detector was designed with consideration of energy deposition characteristics and consists of YAP:Ce or HR-GAGG scintillators in combination with BGO scintillators, employing a photomultiplier tube for signal amplification. Validation procedures included Monte Carlo simulations and measurements using actual radiation sources. Both measurement and simulation results demonstrate a correlation in scintillator energy depositions across different gamma-ray energies. Pulse Shape Discrimination (PSD) plots effectively differentiate between low-energy and high-energy gamma-rays, thereby confirming the predictions from simulations. These results suggest promising potential for developing a sensitive low-energy gamma-ray detector utilizing various scintillator combinations. The phoswich detector shows promise for effectively detecting low-energy gamma-rays emitted by alpha nuclides in piping.