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Journal Articles

Development of a large-area alpha imaging detector for hand and foot monitors

Morishita, Yuki; Higuchi, Mikio*; Kaneko, Junichi*; Kitagawa, Yuichi*; Akedo, Jun*; Soma, Mitsugu*; Matsui, Hiroaki*

Nuclear Instruments and Methods in Physics Research A, 1057, p.168702_1 - 168702_8, 2023/12

https://doi.org/10.1016/j.nima.2023.168702
 Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)

This paper describes the development of a large-area imaging detector capable of measuring the detailed distribution of alpha particles on hands and feet for use in entry/exit control monitors in decommissioning sites such as the Fukushima Daiichi Nuclear Power Plant. The detector was developed using a commercially available ZnS(Ag) scintillator and an electron multiplying CCD camera. The effectiveness of the detector was evaluated by measuring several types of radiation sources, and the results showed that it was possible to detect the position of alpha particles in a very short time, and contamination levels of up to 11 Bq/cm$$^{2}$$ could be visualized. As a result of the minimal detectable surface activity concentration evaluations, 2.0 minutes or more is required to achieve 4 Bq/cm$$^{2}$$, and 25.0 minutes or more is required to achieve 0.4 Bq/cm$$^{2}$$. The field of view of the detector was also checked, and it was confirmed that the setup had a field of view that could cover most of the hand and the sole of the shoe. This detector is expected to be useful for preventing internal uptake and decontamination.

Journal Articles

A Phoswich alpha/beta detector for monitoring in the site of Fukushima Daiichi Nuclear Power Station

Morishita, Yuki; Takasaki, Koji; Kitayama, Yoshiharu; Tagawa, Akihiro; Shibata, Takuya; Hoshi, Katsuya; Kaneko, Junichi*; Higuchi, Mikio*; Oura, Masatoshi*

Radiation Measurements, 160, p.106896_1 - 106896_10, 2023/01

https://doi.org/10.1016/j.radmeas.2022.106896
 Times Cited Count：8 Percentile：87.16(Nuclear Science & Technology)

This study proposes a newly developed phoswich alpha/beta detector that can discriminate alpha and beta particles emitted from the alpha and beta contaminations in the FDNPS site. The phoswich alpha/beta detector is made up of two layers of scintillators that detect alpha and beta particles. The pulse shape discrimination (PSD) method was used to detect alpha particles in high beta particle and high gamma-ray (comparable to gamma-ray dose rate near the FDNPS reactor building) environments. Due to a 23.3% full width at half maximum (FWHM) energy resolution for alpha particles, the detector can be used to distinguish between nuclear fuel materials such as plutonium and its radon progeny (Po-214). Moreover, the detector could distinguish alpha particles from $$^{137}$$Cs gamma rays with a dose rate background up to 9.0 mSv/h. It is the first to demonstrate that the developed phoswich detector can be used to discriminate and measure alpha and beta particles of the actual contaminated FDNPS samples.

Journal Articles

Development of a Gd$$_{2}$$Si$$_{2}$$O$$_{7}$$ (GPS) scintillator-based alpha imaging detector for rapid plutonium detection in high-radon environments

Morishita, Yuki; Izaki, Kenji; Kaneko, Junichi*; Yamamoto, Seiichi*; Higuchi, Mikio*; Torii, Tatsuo

IEEE Transactions on Nuclear Science, 67(10), p.2203 - 2208, 2020/10

https://doi.org/10.1109/TNS.2020.3014997
 Times Cited Count：10 Percentile：69.56(Engineering, Electrical & Electronic)

We developed a Gd$$_{2}$$Si$$_{2}$$O$$_{7}$$ (GPS) scintillator-based alpha imaging detector and demonstrated its effectiveness by evaluating actual Pu particle and $$^{222}$$Rn progeny. The GPS scintillator plate was prepared by a sintering method. The outer dimensions of the GPS scintillator plate were 5 $$times$$ 5 cm, and the scintillator layer was approximately 50 $$mu$$m on a 3-mm-thick high-transparency glass. The plate was optically coupled to a position-sensitive photomultiplier tube with silicone grease. The developed imaging detector exhibited good uniformity. Pu particle activities were accurately evaluated at 14 different positions, and the difference in activity was within 6%. Radon-222 ($$^{222}$$Rn) progeny counts were reduced by 65.3% by applying an energy window. Although the Pu/$$^{222}$$Rn progeny activity ratio was 1/51, the Pu particle was successfully identified among $$^{222}$$Rn progeny within the 5 min-measurement time. The imaging detector has an excellent ability for detecting Pu among $$^{222}$$Rn progeny. Thus, this detector is useful for alpha contamination monitoring in high-radon-background environments.

Journal Articles

Development of an alpha dust monitor using a GPS scintillator plate

Morishita, Yuki; Kaneko, Junichi*; Higuchi, Mikio*; Izaki, Kenji; Yajima, Tatsuo*; Matsuura, Mitsugu*; Tamura, Ken; Torii, Tatsuo

Radiation Measurements, 122, p.115 - 120, 2019/03

https://doi.org/10.1016/j.radmeas.2019.01.011
 Times Cited Count：8 Percentile：59.19(Nuclear Science & Technology)

Journal Articles

Performance comparison of scintillators for alpha particle detectors

Morishita, Yuki; Yamamoto, Seiichi*; Izaki, Kenji; Kaneko, Junichi*; Toi, Kohei*; Tsubota, Yoichi*; Higuchi, Mikio*

Nuclear Instruments and Methods in Physics Research A, 764, p.383 - 386, 2014/11

https://doi.org/10.1016/j.nima.2014.07.046
 Times Cited Count：53 Percentile：96.09(Instruments & Instrumentation)

Oral presentation

Performance comparison of scintillators for alpha particle detectors

Morishita, Yuki; Yamamoto, Seiichi*; Izaki, Kenji; Kaneko, Junichi*; Toi, Kohei*; Tsubota, Yoichi*; Higuchi, Mikio*

no journal, , 

Oral presentation

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$$_{3}$$(Ga,Al)$$_{5}$$O$$_{12}$$ (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 ($$sim$$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 Gd$$_{2}$$Si$$_{2}$$O$$_{7}$$ (GPS) scintillator plate and a photomultiplier tube (PMT). The energy resolution for 5.5-MeV alpha particles was $$sim$$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.

Oral presentation

Development of a large-area alpha imaging detector capable of measuring the detailed distribution of alpha contaminations on hands and feet

Morishita, Yuki; Higuchi, Mikio*; Kaneko, Junichi*; Kitagawa, Yuichi*; Akedo, Jun*; Soma, Mitsugu*; Matsui, Hiroaki*

no journal, , 

This paper describes the development of a large-area imaging detector capable of measuring the detailed distribution of alpha particles on hands and feet for use in entry/exit control monitors in decommissioning sites such as the Fukushima Daiichi Nuclear Power Plant. The detector was developed using a commercially available ZnS(Ag) scintillator and an electron multiplying CCD camera. The effectiveness of the detector was evaluated by measuring several types of radiation sources, and the results showed that it was possible to detect the position of alpha particles in a very short time, and contamination levels of up to 11 Bq/cm$$^{2}$$ could be visualized. The field of view of the detector was also checked, and it was confirmed that the setup had a field of view that could cover most of the hand and the sole of the shoe. This detector is expected to be useful for preventing internal uptake and decontamination.

Oral presentation

An $$alpha$$ particle measurement experiment by a GPS:Ce scintillator

Kaneko, Junichi*; Kondo, Kaori*; Tsubota, Yoichi*; Higuchi, Mikio*; Fujita, Fumiyuki*; Izaki, Kenji

no journal, , 

no abstracts in English

Oral presentation

Light yield maximization of triclinic La-GPS scintillator by optimizing La and Ce concentration

Tsubota, Yoichi; Waki, Takaaki*; Kaneko, Junichi*; Higuchi, Mikio*; Ishibashi, Hiroyuki*

no journal, , 

Gd$$_{2}$$Si$$_{2}$$O$$_{7}$$:Ce (GPS) is a rare-earth oxide scintillator with large light yield (LY) exceed NaI:Tl and can be used under high temp. environment. The triclinic La-GPS, which substituted Gd site for La, also have LY close to NaI:Tl. Although several trials on growth of La-GPS were reported, systematic research on LY were not sufficiently carried out. In this report, the optimization of La and Ce concentration of La-GPS was conducted to maximize LY. Sintered (LaxGd1-x-yCey)$$_{2}$$Si$$_{2}$$O$$_{7}$$ (x= 0.1, y= 0 - 0.16) and (x= 0 - 0.15, y= 0.025) were fixed on glass plates and mechanically polished to be approx. 100 micro-meter thick. For the evaluation of scintillation LY, alpha-particle response measurement using $$^{241}$$Am was performed. For the Ce= 2.5% samples, La-GPS with 5 - 6.7% of La showed the highest LY. LY was then decreased as the La increased. For the La=10% samples, light yield increased as Ce increased in the range of Ce=0.5-2.5% that corresponded with the increase of luminescent center of Ce$$^{3+}$$. Decrease of LY due to concentration quenching was observed in the range of Ce$$>$$4%.

Oral presentation

Application test of GPS scintillator plates for an alpha particle dust monitor

Toi, Kohei*; Shimaoka, Takehiro*; Kaneko, Junichi*; Izaki, Kenji; Tsubota, Yoichi*; Higuchi, Mikio*; Nishiyama, Shusuke*

no journal, , 

no abstracts in English

Oral presentation

Investigation on plutonium discrimination by function of energy and position detection

Morishita, Yuki; Izaki, Kenji; Mizuniwa, Harumi; Kaneko, Junichi*; Shimaoka, Takehiro*; Tsubota, Yoichi*; Higuchi, Mikio*; Toi, Kohei*

no journal, , 

no abstracts in English

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