Neutron/-ray discrimination based on the property and thickness controls of scintillators using Li glass and LiCAF(Ce) in a -ray field

Kaburagi, Masaaki; Shimazoe, Kenji*; Terasaka, Yuta; Tomita, Hideki*; Yoshihashi, Sachiko*; Yamazaki, Atsushi*; Uritani, Akira*; Takahashi, Hiroyuki*

Nuclear Instruments and Methods in Physics Research A, 1046, p.167636_1 - 167636_8, 2023/01

https://doi.org/10.1016/j.nima.2022.167636

We focus on the thickness and property controls of inorganic scintillators used for thermal neutron detection in intense -ray fields without considering pulse shape discrimination techniques. GS20 (a lithium glass) and LiCaAlF:Ce(LiCAF:Ce) cintillators with thicknesses of 0.5 and 1.0 mm, respectively, have been employed. Pulse signals generated by photomultiplier tubes, to which the scintillators were coupled, were inserted into a digital pulse processing unit with 1 Gsps, and the areas of waveforms were integrated for 360 ns. In a Co -ray field, the neutron detection for GS20 with a 0.5-mm thickness was possible at dose rates of up to 0.919 Gy/h; however, for LiCAF:Ce, neutron detection was possible at 0.473 Gy/h, and it failed at 0.709 Gy/h. Threfore, in a Co -ray field, the neutron/-ray discrimination of GS20 was better than that of LiCAF:Ce due to its better energy resolution and higher detection efficiency.

Improvement of analysis results from the GAGG scintillator Compton camera operated on an unmanned helicopter by selecting stable flight conditions

Shikaze, Yoshiaki; Shimazoe, Kenji*

Journal of Nuclear Science and Technology, 59(1), p.44 - 54, 2022/01

https://doi.org/10.1080/00223131.2021.1948452

A Compton camera system for use on an unmanned helicopter was previously developed for characterizing the distribution of radioactive materials in highly contaminated areas. For this study, a small camera, a laser distance meter, an attitude angles sensor, temperature sensors, and real-time monitoring software were equipped to the Compton camera system to better measure flight parameters and to more precisely detect hot spot locations. To confirm if detection results were improved by the modifications, measurements were taken from hovering and programmed flights over a field in Okuma, Fukushima Prefecture (Japan). Ambient dose equivalent rate distributions at ground level were obtained by processing the flight data, then compared against measurements taken at ground level on foot using a survey meter. For one hovering flight, the correlation between the datasets was improved by selecting a period of stable flight position and attitude, and by restricting the deviation of the attitude angles. Between 6.0%-7.6% improvement in the position resolution was achieved by using the data from stable flight periods, even when using 1 minute data windows. The precision of hot spot detections and ambient dose equivalent rate distributions obtained from the Compton camera were thus improved by the aforementioned modifications to the system.

Gamma-ray spectroscopy with a CeBr scintillator under intense -ray fields for nuclear decommissioning

Kaburagi, Masaaki; Shimazoe, Kenji*; Kato, Masahiro*; Kurosawa, Tadahiro*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*; et al.

Nuclear Instruments and Methods in Physics Research A, 988, p.164900_1 - 164900_8, 2021/02

https://doi.org/10.1016/j.nima.2020.164900

An increasing number of nuclear facilities have been decommissioned worldwide following the 2011 accident of the TEPCO' Fukushima Daiichi Nuclear Power Station. During the decommissioning, radioactive materials have to be retrieved under proper management. In this study, a small cubic CeBr spectrometer with dimensions of 5 mm 5 mm 5 mm was manufactured to perform -ray spectroscopy under intense -ray fields. Furthermore, thanks to a fast digital process unit and a customized photomultiplier, the device could perform -ray spectroscopy at dose rates of over 1 Sv/h. The energy resolution (FWHM) at 662 keV ranged from 4.4% at 22 mSv/h to 5.2% at 1407 mSv/h for a Cs radiation field. Correspondingly, at 1333 keV, it ranged from 3.1% at 26 mSv/h to 4.2% at 2221 mSv/h for a Co radiation field, which suggested to realize -ray assessment of Cs, Cs, Co, and Eu at dose rates of over 1 Sv/h.

Gamma-ray imaging system for Fukushima Daiichi Nuclear Power Plant using silicon strip detector

Kaburagi, Masaaki; Sato, Yuki; Yoshihara, Yuri*; Shimazoe, Kenji*; Takahashi, Hiroyuki*; Torii, Tatsuo

Reactor Dosimetry; 16th International Symposium on Reactor Dosimetry (ISRD-16) (ASTM STP 1608), p.405 - 414, 2018/11

https://doi.org/10.1520/STP160820170070

The Dynamic time-over-threshold method for multi-channel APD based gamma-ray detectors

Orita, Tadashi; Shimazoe, Kenji*; Takahashi, Hiroyuki*

Nuclear Instruments and Methods in Physics Research A, 775, p.154 - 161, 2015/03

https://doi.org/10.1016/j.nima.2014.12.014

Recent advances in manufacturing technology have enabled the use of multichannel pixelated detectors in gamma ray imaging applications. When obtaining gamma ray measurements, it is important to obtain pulse height information in order to avoid unnecessary events such as scattering. However, as the number of channels increases, more electronics are needed to process each channel's signal, and the corresponding increases in circuit size and power consumption can result in practical problems. The time over threshold (ToT) method, which has recently become popular in the medical field, is a signal processing technique that can effectively avoid such problems. However, ToT suffers from poor linearity and its dynamic range is limited. We therefore propose a new ToT technique called the dynamic time over threshold (dToT) method. A new signal processing system using dToT and CRRC shaping demonstrated much better linearity than that of a conventional ToT. Using a test circuit with a new GdAlGaO (GAGG) scintillator and an avalanche photodiode, the pulse height spectra of Cs and Na sources were measured with high linearity. Based on these results, we designed a new application specific integrated circuit (ASIC) for this multichannel dToT system, measured the spectra of a Na source, and investigated the linearity of the system.

Introduction to multi Cubic high energy gamma-ray spectrometer

Kaburagi, Masaaki; Shimazoe, Kenji*; Otaka, Yutaka*; Uenomachi, Mizuki*; Kamada, Kei*; Kim, J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*; et al.

no journal, , 

Performance study of multi cubic high energy -ray spectrometric system for the decommissioning of the Tokyo Electric Power Company Fukushima Daiichi Nuclear Power Station

Kaburagi, Masaaki; Shimazoe, Kenji*; Otaka, Yutaka*; Uenomachi, Mizuki*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*; et al.

no journal, , 

The retrieval of the nuclear fuel debris, which is the substance including melted nuclear fuel and structural materials, will be started from fiscal 2021. Then, as a non-destructive analysis technology of the nuclear fuel debris, a -ray spectroscopy system is being developed to measure high energy rays due to Eu and nuclear reactions under high dose rate, which was composed of a CeBr cubic, photomultiplier tube, and fast signal processing unit. This presentation reports that the exposure study of the detector system was performed for a Co field at the dose rates of up to 750 mSv/h, and the detector response was investigated at each dose rate.

Remote control technology for monitoring inside RPV pedestal during retrieval of fuel debris

Matsuhira, Nobuto*; Komatsu, Ren*; Nakashima, Shinsuke*; Yamashita, Atsushi*; Fukui, Rui*; Takahashi, Hiroyuki*; Shimazoe, Kenji*; Woo, H.*; Tamura, Yusuke*; Takashi, Takayuki*; et al.

no journal, , 

Remote control technology for monitoring inside RPV pedestal during retrieval of fuel debris; Integrated experiments

Matsuhira, Nobuto*; Komatsu, Ren*; Nakashima, Shinsuke*; Yamashita, Atsushi*; Fukui, Rui*; Takahashi, Hiroyuki*; Shimazoe, Kenji*; Woo, H.*; Tamura, Yusuke*; Takashi, Takayuki*; et al.

no journal, , 

-ray imaging system for Fukushima Daiichi Nuclear Power Plant using silicon strip detector

Kaburagi, Masaaki; Sato, Yuki; Yoshihara, Yuri*; Shimazoe, Kenji*; Takahashi, Hiroyuki*; Torii, Tatsuo

no journal, ,