Neutron transmission CB-KID imager using samples placed at room temperature

Ishida, Takekazu*; Vu, TheDang*; Shishido, Hiroaki*; Aizawa, Kazuya; Oku, Takayuki; Oikawa, Kenichi; Harada, Masahide; Kojima, Kenji M*; Miyajima, Shigeyuki*; Koyama, Tomio*; et al.

Journal of Low Temperature Physics, 214(3-4), p.152 - 157, 2024/02

https://doi.org/10.1007/s10909-023-03030-9

Radioisotope identification algorithm using deep artificial neural network for supporting nuclear detection and first response on nuclear security incidents

Kimura, Yoshiki; Tsuchiya, Kenichi*

Radioisotopes, 72(2), p.121 - 139, 2023/07

https://doi.org/10.3769/radioisotopes.72.121

Rapid and precise radioisotope identification in the scene of nuclear detection and nuclear security incidents is one of the challenging issues for the prompt response on the detection alarm or the incidents. A radioisotope identification algorithm using a deep artificial neural network model applicable to handheld gamma-ray detectors has been proposed in the present paper. The proposed algorithm automatically identifies gamma-emitting radioisotopes based on the count contribution ratio (CCR) from each of them estimated by the deep artificial neural network model trained by simulated gamma-ray spectra. The automated radioisotope identification algorithm can support first responders of nuclear detection and nuclear security incidents without sufficient experience and knowledge in radiation measurement. The authors tested the performance of the proposed algorithm using two different types of deep artificial neural network models in application to handheld detectors having high or low energy resolution. The proposed algorithm showed high performance in identifying artificial radioisotopes for actually measured gamma-ray spectra. It was also confirmed that the algorithm is applicable to identifying U and automated uranium categorization by analyzing estimated CCRs by the deep artificial neural network models. The authors also com-pared the performance of the proposed algorithm with a conventional radioisotope identification method and discussed promising ways to improve the performance of the algorithm using the deep artificial neural network.

Shield-free directional gamma-ray detector using small-angle Compton scattering

Kitayama, Yoshiharu

Gamma Ray Imaging; Technology and Applications, p.165 - 179, 2023/00

https://doi.org/10.1007/978-3-031-30666-2

A gamma-ray imager is a powerful tool for visualizing the distribution of radioactive materials. Recently, it has been applied to the decommissioning site of the Fukushima Daiichi Nuclear Power Station. At the decommissioning site, an imager compact, lightweight, and capable of quantitative evaluation of radioactivity is demanded. The Gamma-ray Imager using Small-Angle Scattering (GISAS) was proposed as a gamma-ray imager that meets all these requirements. GISAS consists of several shield-free directional gamma-ray detectors that detect only small-angle Compton scattering. Simulations and experiments verified the feasibility of the shield-free directional gamma-ray detectors. The shield-free directional gamma-ray detector consists of a scatterer that detects small-angle Compton scattering and an absorber that detects the scattered gamma rays. By setting an appropriate energy window for each detector, only scattering events that can be considered almost straightforward are detected. Through simulations and experiments, we have confirmed that using a silicon drift detector as the scatterer and a Gd3Al2Ga3O12 scintillator as the absorber, we can detect only small-angle Compton scattering events and obtain directionality for 662 keV gamma rays.

Absolute quantification of Cs activity in spent nuclear fuel with calculated detector response function

Sato, Shunsuke*; Nauchi, Yasushi*; Hayakawa, Takehito*; Kimura, Yasuhiko; Kashima, Takao*; Futakami, Kazuhiro*; Suyama, Kenya

Journal of Nuclear Science and Technology, 60(6), p.615 - 623, 2022/06

https://doi.org/10.1080/00223131.2022.2130462

A new non-destructive method for evaluating Cs activity in spent nuclear fuels was proposed and experimentally demonstrated for physical measurements in burnup credit implementation. Cs activities were quantified using gamma ray measurements and numerical detector response simulations without reference fuels, in which Cs activities are well known. Fuel samples were obtained from a lead use assembly (LUA) irradiated in a commercial pressurized water reactor (PWR) up to 53 GWd/t. Gamma rays emitted from the samples were measured using a bismuth germinate (BGO) scintillation detector through a collimator attached to a hot cell. The detection efficiency of gamma rays with the detector was calculated using the PHITS particle transport calculation code considering the measurement geometry. The relative activities of Cs, Cs, and Eu in the sample were measured with a high-purity germanium (HPGe) detector for more accurate simulations of the detector response for the samples. The absolute efficiency of the detector was calibrated by measuring a standard gamma ray source in another geometry. Cs activity in the fuel samples was quantified using the measured count rate and detection efficiency. The quantified Cs activities agreed well with those estimated using the MVP-BURN depletion calculation code.

Calculation code of output current for self-powered radiation detector; Algorithm construction and comparison of calculation results

Shibata, Hiroshi; Takeuchi, Tomoaki; Seki, Misaki; Shibata, Akira; Nakamura, Jinichi; Ide, Hiroshi

JAEA-Data/Code 2021-018, 42 Pages, 2022/03

JAEA-Data-Code-2021-018.pdf:2.78MB
JAEA-Data-Code-2021-018-appendix(CD-ROM).zip:0.15MB

Japan Materials Testing Reactor (JMTR) in Oarai Research and Development Institute of the Japan Atomic Energy Agency has been developing various reactor materials, irradiation techniques and instruments for more than 30 years. Among them, the development of self-powered neutron detectors (SPNDs) and gamma detectors (SPGDs) has been carried out, and several research results have been reported. However, most of the results are based on the design study of the detector development and the results of in-core irradiation tests and gamma irradiation tests using Cobalt-60. In this report, a numerical code is developed based on the paper "Neutron and Gamma-Ray Effects on Self-Powered In-Core Radiation Detectors" written by H.D. Warren and N.H. Shah in 1974, in order to theoretically evaluate the self-powered radiation detectors.

Monitoring technique for detection of nuclear and radioactive materials on major public events

Mochimaru, Takanori*; Koizumi, Mitsuo; Takahashi, Tone; Hironaka, Kota; Kimura, Yoshiki; Sato, Yuki; Terasaka, Yuta; Yamanishi, Hirokuni*; Wakabayashi, Genichiro*

Dai-42-Kai Nihon Kaku Busshitsu Kanri Gakkai Nenji Taikai Kaigi Rombunshu (Internet), 4 Pages, 2021/11

no abstracts in English

Two-dimensional scintillation neutron detectors for the extension of SENJU diffractometer

Nakamura, Tatsuya; To, Kentaro; Koizumi, Tomokatsu; Kiyanagi, Ryoji; Ohara, Takashi; Ebine, Masumi; Sakasai, Kaoru

Proceedings of 2020 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC 2020), Vol.1, p.483 - 484, 2021/09

https://doi.org/10.1109/NSS/MIC42677.2020.9507813

Two-dimensional neutron detectors were developed for the extension of SENJU time-of-flight Laue single crystal neutron diffractometer in J-PARC MLF. The detectors are to be installed at the additional detector bank for the SENJU instrument. The detector module is made based on ZnS scintillator and wavelength-shifting fiber technology, where each detector module maintains a neutron-sensitive area of 256256 mm with a pixel size of 44 mm. To meet the tight space limitation in the instrument, the detector was designed as compact as possible. The detector has a depth of 170 mm, which is about 40% smaller than that of the original SENJU detector. All four produced detectors exhibited similar detector performances: detection efficiency 50-60% for 2- neutron, Co gamma-ray sensitivity 110, count uniformity 3-6%.

Radon measurements with a compact, organic-scintillator-based alpha/beta spectrometer

Morishita, Yuki; Ye, Y.*; Mata, L.*; Pozzi, S. A.*; Kearfott, K. J.*

Radiation Measurements, 137, p.106428_1 - 106428_7, 2020/09

https://doi.org/10.1016/j.radmeas.2020.106428

We have developed a compact, organic-scintillator-based alpha/beta spectrometer for radon measurements and have characterized it using a unique, small radon chamber. The spectrometer is composed of a through-silicon via (TSV) silicon photomultiplier (or SiPM) and a 6 mm 6 mm 6 mm stilbene crystal cube. Analog signals from the SiPM are sent to a digitizer. The detector is housed in a light-tight box, with a stacked air filter installed in one side of the box to enable Rn gas to diffuse to the inside. We conducted one experiment with the spectrometer and an AlphaGUARD detector placed in a basement at the University of Michigan, and we conducted other experiments with both detectors placed in a small radon chamber together with Ra sources. By applying a pulse-shape-discrimination technique, we were able to separate the alpha and beta spectra simultaneously and clearly and to measure them quantitatively. We found two peaks in the measured alpha spectrum: a lower-energy peak due to Po and a higher-energy peak due to Po. We found a linear relation between the radon concentration y from AlphaGUARD and the counting rates from the stilbene-SiPM detector. The alpha/beta spectrometer is less than 10 mm thick, and we expect that it will be easy to increase the sensitivity with future device construction. Thus, this compact, organic-scintillator-based alpha/beta spectrometer shows promise for use in novel radon-detection systems.

A Submillimeter spatial resolution scintillation detector for time-of-flight neutron diffraction imaging

Nakamura, Tatsuya; Kawasaki, Takuro; To, Kentaro; Tsutsui, Noriaki; Ebine, Masumi; Birumachi, Atsushi; Sakasai, Kaoru

Proceedings of 2018 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC 2018) (Internet), 3 Pages, 2019/10

https://doi.org/10.1109/NSSMIC.2018.8824447

A two-dimensional scintillation neutron detector with a submillimeter spatial resolution was developed for pulsed neutron diffraction imaging at the J-PARC MLF. The detector comprised the thin, single ZnS/LiF scintillator screen coupled with the crossed wavelength-shifting fiber array for light collection. For a high spatial resolution, the wavelength shifting fibers with diameter of 0.1 mm were used them for assembling the detector. The prototype detector that has a neutron-sensitive area of 24 24 mm exhibited a spatial resolution of 0.200.06 mm and 0.160.06 mm for x and y directions, respectively. The detector had a detection efficiency of 7 for thermal neutrons with a Co -ray sensitivity in the order of 10. In this paper detailed detector design is presented together with experimental results using the pulsed neutron beam.

Characteristics of commercially available CdZnTe detector as gamma-ray spectrometer under severe nuclear accident

Tanimura, Yoshihiko; Nishino, Sho; Yoshitomi, Hiroshi; Kowatari, Munehiko; Oishi, Tetsuya

Progress in Nuclear Science and Technology (Internet), 6, p.134 - 138, 2019/01

https://doi.org/10.15669/pnst.6.134

At the severe nuclear accidents like the Fukushima Daiichi Nuclear Power Plant, various radionuclides will be dispersed into the environment and raise the dose rate. The - measurements of ray spectra and identifying radionuclides using the results are important for the radiological protection from both external and internal exposure. For this application a commercially available CdZnTe spectrometer (Kromek GR-1) was characterized at the calibration fields of FRS/JAEA. The angular dependence of the detection efficiency was studied and the efficiency was kept within 15 % degradation in 135 degree incident angle, which covers 85 % of all. The usable dose range was evaluated and the spectrometer could correctly measure the ray spectra below 200 Gy/h.