A Remote continuous air monitoring system for measuring airborne alpha contamination

Morishita, Yuki; Usami, Hiroshi; Furuta, Yoshihiro; Aoki, Katsunori; Tsurudome, Koji; Hoshi, Katsuya; Torii, Tatsuo

Radiation Protection Dosimetry, 189(2), p.172 - 181, 2020/04

https://doi.org/10.1093/rpd/ncaa028

We developed a remote continuous air monitoring (RCAM) system. The RCAM system consisted of a personal air monitor and a robot. The personal air monitor (poCAMon, SARAD, Germany) had a 400 mm ion-injected silicon detector and a membrane air filter with 25 mm-diameter. The personal air monitor provides the alpha energy spectra for any measurement time interval. Demonstration measurements were taken underground at the Mizunami Underground Research Laboratory (MIU) and at a poorly ventilated concrete building. The RCAM system was remotely operated and successfully measured the Rn progeny even though the relative humidity (RH) was almost 100%. In the measured alpha spectra, the peaks of Po (6.0 MeV alpha) and Po (7.7 MeV alpha) were clearly identified. Our developed monitor is promising for alpha dust monitoring in a high gamma-ray environment or contaminated areas where a worker cannot safely physically enter.

Detection of alpha particle emitters originating from nuclear fuel inside reactor building of Fukushima Daiichi Nuclear Power Plant

Morishita, Yuki; Torii, Tatsuo; Usami, Hiroshi; Kikuchi, Hiroyuki*; Utsugi, Wataru*; Takahira, Shiro*

Scientific Reports (Internet), 9, p.581_1 - 581_14, 2019/01

https://doi.org/10.1038/s41598-018-36962-4

Remote technology development for function advancement of research base-development of small, 6; Diameter self-powered critical monitoring sensor

Usami, Hiroshi; Kawamura, Hiroshi; Ooka, Makoto; Miura, Kuniaki*; Onizawa, Tatsuya*

no journal, , 

no abstracts in English

Development of radiation imaging system integrating radiation measurement and optical three-dimensional measurement

Sato, Yuki; Tanifuji, Yuta; Terasaka, Yuta; Usami, Hiroshi; Kaburagi, Masaaki; Miyamura, Hiroko; Kawabata, Kuniaki; Torii, Tatsuo

no journal, , 

no abstracts in English

Visualization of radioactive substances by integrating radiation measurement and 3D optical measurement inside the Fukushima Daiichi Nuclear Power Station

Sato, Yuki; Tanifuji, Yuta; Terasaka, Yuta; Morishita, Yuki; Usami, Hiroshi; Kaburagi, Masaaki; Kawabata, Kuniaki; Torii, Tatsuo

no journal, , 

3-D sensing technologies of radioactive substances and environmental structure inside the Fukushima Daiichi Nuclear Power Station

Tanifuji, Yuta; Sato, Yuki; Usami, Hiroshi; Kaburagi, Masaaki; Kawabata, Kuniaki; Torii, Tatsuo

no journal, , 

The Development of the radiation imaging camera for the radioactive contamination monitoring in Fukushima Daiichi Nuclear Power Station

Kaburagi, Masaaki; Sato, Yuki; Morishita, Yuki; Usami, Hiroshi; Terasaka, Yuta; Furuta, Yoshihiro; Torii, Tatsuo

no journal, , 

The 45th annual Waste Management Symposium in a forum for discussing and seeking safe and cost-effective solutions to managing and dispositioning radioactive waste and decommissioning nuclear facilities is hold, JAEA participates in it as the exhibitor. This is the introduction of the radiation imaging technology, which is one of the R&D of the acceleration of the decommissioning of the TEPCO's Fukushima Daiichi Nuclear Station.

Feasibility study on a red-emitting-scintillation probe with an optical fiber for a high-rate dose-monitor

Kodama, Shohei*; Kurosawa, Shunsuke*; Morishita, Yuki; Usami, Hiroshi; Hayashi, Masateru*; Tanaka, Hiroki*; Yoshino, Masao*; Kamada, Kei*; Yoshikawa, Akira*; Torii, Tatsuo

no journal, , 

After Fukushima 1st Nuclear Plant accident, a large number of radioactive pollutants or nuclear debris with very high dose of more than a few Sv/h still have existed. To estimate the dose of such pollutants, a Japan Atomic Energy Agency research group has suggested a new technique to use a long optical fiber and a red-emitting scintillator, and the scintillation photons are read outside of high dose area. We tested the gamma-ray detection performance of a ruby (Cr:AlO) and a newly developed CsHfI scintillators as a scintillating probe coupled with an optical fiber in this study.

Detection of alpha particle emitters originating from nuclear fuel inside reactor building of Fukushima Daiichi Nuclear Power Station

Morishita, Yuki; Torii, Tatsuo; Usami, Hiroshi; Kikuchi, Hiroyuki*; Utsugi, Wataru*; Takahira, Shiro*

no journal, , 

We measured alpha emitters obtained from a reactor building in the Fukushima Daiichi Nuclear Power Plant (FDNPP) by using an alpha particle imaging detector. For developing the detector, we used a very thin (0.05-mm-thick) a cerium-doped Gd(Ga,Al) O (Ce GAGG) scintillator and silicon photomultiplier (SiPM) arrays as the photodetector. The floor of the reactor building in FDNPP was wiped off by using smear papers, and the radioactivity of these papers was measured by the alpha particle imaging detector. In addition, we measured a Plutonium (Pu) sample (mainly 5.5 MeV alpha particles from Pu) obtained from a nuclear fuel facility by using of the same detector for comparison with the smear papers. The alpha spectrum was in the energy range of 5-6 MeV, which corresponds to the alpha particle energy of Pu (5.5 MeV). The correlation coefficient of the alpha spectra of the smear papers and the Pu sample had a strong positive linear relation. Moreover, the peak of Am was identified by gamma spectrum measurement. Based on these results, it is highly likely that the alpha emitters in the reactor building of FDNPP are Pu and Am, which originated from the nuclear fuel. The surface contamination level of alpha emitters exceeded 4 Bq/cm.

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

no journal, , 

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.