Development of alpha particle detectors for detecting radiological contamination

Morishita, Yuki   ; Izaki, Kenji ; Kaneko, Junichi* ; Higuchi, Mikio*; Tamura, Ken; Usami, Hiroshi; Kikuchi, Hiroyuki*; Utsugi, Wataru*; Takahira, Shiro*; Torii, Tatsuo  

We have developed new alpha particle detectors for detecting the alpha contaminations accurately and instantaneously: alpha imaging detectors and alpha dust monitors. For the development of the alpha imaging detector, we used a thin cerium-doped Gd(Ga,Al)O (Ce: GAGG) scintillator and silicon photomultipliers (SiPMs). The thin GAGG scintillator was optically coupled to a light-guide and the SiPMs for the detector fabrication. The detector showed a good energy resolution for 5.5 MeV alpha particles (13 % at the full width at half maximum (FWHM)). The detector is capable of capturing two-dimensional alpha images. This detector also has the advantage of its compact size, which enables to measure the alpha contaminations in narrow spaces. We demonstrated the actual measurement of smear samples obtained from the Fukushima Daiichi Nuclear Power Station using the developed imaging detector. Commercial alpha dust monitors with a silicon surface barrier detector (SSBD) operating at some nuclear facilities frequently produced false alarms due to environmental conditions such as humidity. For the development of the alpha dust monitor, we used a cerium-doped GdSiO (GPS) scintillator plate and a photomultiplier tube (PMT). The energy resolution for 5.5-MeV alpha particles was 12% FWHM. The count-rate of the radon progeny decreased by 77% with applying energy discrimination. The alpha dust monitor was capable of conducting alpha-particle spectroscopy even though the GPS scintillator got wet. The alpha dust monitor is an ideal choice for in places lacking temperature and humidity controls. In the presentation at the IRPA 15 conference, we will present the developments and measurement results of these alpha detectors.