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Nakamura, Tatsuya; To, Kentaro; Kiyanagi, Ryoji; Ohara, Takashi; Hosoya, Takaaki; Sakasai, Kaoru
no journal, ,
Detector performances of large area two-dimensional neutron detectors produced for upgrade of SENJU diffractometer at Materials and Life science experimental Facility at J-PARC have been evaluated. The detectors are developed based on a 
Li:ZnS(Ag) scintillator and wavelength-shifting fiber technology. The prototype detector has a neutron-sensitive area of 512 
768 mm, which is six-fold of the original detector installed in the SENJU. The prototype detector exhibited a detection efficiency of 40-50% for 2-
space neutrons and 
Co gamma-ray sensitivity of ~10
. 9 detector modules have been produced for the planned SENJU upgrade. The produced detectors exhibited similar detector efficiencies and gamma-ray sensitivities to that of the prototype detector. Neutron counts of these detectors with a 
Cf source varied within 5% to the average. The experimental results of the prototype and the produced beamline detectors are presented.
Toh, Yosuke; Maeda, Makoto; Komeda, Masao
no journal, ,
-ray nuclide in an intense -ray field for nuclear decommissioningKaburagi, Masaaki; Ishii, Junya*; Kato, Masahiro*
no journal, ,
Morishita, Yuki; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*
no journal, ,
The Fukushima Daiichi Nuclear Power Station's decommissioning requires thorough inspection of piping for contamination, including alpha nuclides. External alpha particle measurements are impossible, necessitating gamma-ray detection methods. A phoswich detector for low-energy gamma-ray detection was developed and validated experimentally at a nuclear fuel facility. The detector was designed considering energy deposition characteristics. The detector comprises YAlO
:Ce and Bi
GeO
scintillators with a photomultiplier tube for signal amplification. Measurement and simulation results show correlation between scintillator energy depositions for different gamma-ray energies. Pulse Shape Discrimination (PSD) plots distinguish alpha particles and gamma-rays, confirming simulation predictions. Nuclear fuel facility measurements exhibit higher energy deposition in the first scintillator layer. This suggests potential for developing a sensitive low-energy gamma-ray detector using scintillator combinations. Future work aims to optimize detector design and conduct field tests for validation.
Morishita, Yuki; Sato, Yuki; Terasaka, Yuta; Ichiba, Yuta*
no journal, ,
Understanding and assessing alpha and beta contaminations are crucial for the safe decommissioning of nuclear sites like the Fukushima Daiichi Nuclear Power Station (FDNPS). However, conventional methods face challenges, particularly in high-gamma dose-rate environments. This study presents a novel approach utilizing a phoswich detector for direct in-situ detection of alpha and beta particles. The phoswich detector design is tailored to the anticipated higher beta radioactivity at the FDNPS site, comprising a ZnS(Ag) scintillator for alpha detection and a plastic scintillator for beta detection. The distinctive decay times of the scintillators enable discrimination between alpha and beta particles. Experimental measurements involved both radiation sources and on-site measurements. Results demonstrate successful discrimination of alpha and beta particles, with clear separation of clusters in Pulse Shape Discrimination (PSD) maps. The counting efficiency for alpha particles reached 55.6%, while beta particles were separated. Simultaneous measurement of alpha and beta particles further validates the detector's efficacy, with distinct clusters observed for both types of radiation. Field measurements conducted within the FDNPS site confirm the phoswich detector's effectiveness in real-world scenarios. Future studies will report detailed measurements from the site. Overall, the developed phoswich detector offers a promising solution for direct and accurate alpha/beta contamination detection, facilitating enhanced radiation protection and internal exposure assessment in nuclear decommissioning efforts.
Fujisawa, Makoto; Morishita, Yuki; Sagawa, Naoki; Kurosawa, Shunsuke*; Sasano, Makoto*; Hayashi, Masateru*
no journal, ,
The measurement of alpha contamination, or alpha radiation, is important for the decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS). It is very important to verify whether alpha particles can be visualized in a situation where alpha, beta, gamma-rays are mixed together. In this study, we applied our newly developed alpha imager to the measurement of actual samples containing a mixture of alpha, beta, and gamma nuclides, and verified its effectiveness. The alpha imager consisted of a qCMOS camera (ORCA-Quest (C15550-20UP)) and an optical microscope (BX53MRF-S from Olympus). A ZnS(Ag) scintillator with a thickness of 3.25 mg/cm
was used for alpha measurements by placing the scintillator closely over a sample. An 
Am alpha standard source was measured to verify whether alpha particles could be measured. In addition, samples containing a mixture of alpha, beta, and gamma nuclides were measured. Image processing was used to extract clusters of alpha particles. By applying image processing, clusters of alpha particles were successfully extracted. When measuring a sample with a mixture of alpha, beta, and gamma nuclides, clusters of alpha particles could be confirmed. Although the sample had a higher beta activity than alpha activity, only alpha particles were successfully extracted. The developed alpha imager will be useful for contamination measurement in the site of FDNPS.
To, Kentaro; Nakamura, Tatsuya; Sakasai, Kaoru; Yamagishi, Hideshi*
no journal, ,
Sagawa, Naoki; Morishita, Yuki; Fujisawa, Makoto; Kurosawa, Shunsuke*; Sasano, Makoto*; Hayashi, Masateru*
no journal, ,
At nuclear facilities that handle plutonium, visualization of Pu particles in working environment is important for evaluating internal exposure doses for workers. In this study, a new type of Quantitative Complementary Metal Oxide Semiconductor (qCMOS) camera with low noise signals and high readout speed has been used in the alpha imaging system to improve the spatial resolution for alpha-rays and to visualize Pu particles. In addition, effects of irradiation on the system have been confirmed with various types of radiation. As a result, it was found that only alpha rays can be measured specifically by setting a threshold in terms of area, even if noise is generated, without the influence of beta rays, gamma rays, or neutrons.
Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*
no journal, ,