Remote alpha/beta measurement system with support vector machine algorithm

Morishita, Yuki; Miyamura, Hiroko; Sato, Yuki; Matsubara, Jun*; Sumali, B.*; Mitsukura, Yasue*

Nuclear Instruments and Methods in Physics Research A, p.170368_1 - 170368_16, 2025/03

https://doi.org/10.1016/j.nima.2025.170368

Decommissioning nuclear reactor sites presents challenges due to the presence of various radionuclides, including alpha emitters (e.g., Pu, Am, Cm) and beta emitters (e.g., Cs, Sr-Y), which pose significant internal exposure risks to workers. Traditional measurement methods require multiple instruments and are time-consuming, particularly in high gamma-ray environments. To address these issues, we developed a remote alpha and beta discrimination measurement system that integrates a stilbene scintillator detector with a silicon photomultiplier, enabling simultaneous detection of both alpha and beta particles. This study further incorporates machine learning techniques, specifically Support Vector Machines (SVM), for automatic discrimination, eliminating the need for user-defined thresholds and ensuring consistent operational conditions. The system was tested with known radiation sources, demonstrating over 96% classification accuracy for alpha and beta particles. Measurements conducted in motion effectively identified contamination sources, confirming the system's capability for real-time analysis. This innovative approach enhances radiation safety and efficiency in nuclear decommissioning operations, making it particularly beneficial in environments where human access is limited.

An Alpha imaging detector for on-site measurement of Plutonium and Neptunium

Morishita, Yuki; DiPrete, D. P.*; Deason, T.*; Nagaishi, Ryuji

Radiation Measurements, 181, p.107366_1 - 107366_8, 2025/02

https://doi.org/10.1016/j.radmeas.2024.107366

Nuclear fuel materials such as Plutonium (Pu) and Neptunium (Np) are produced as by-products of reprocessing operations, necessitating precise understanding of their contamination distribution within controlled areas for radiation protection. This study presents the development and application of an alpha particle imaging detector for on-site detection of Pu and Np contamination. The detector's performance was evaluated using various alpha sources, demonstrating promising energy resolution and spatial resolution. Subsequently, Pu and Np oxide samples were measured at the Savannah River National Laboratory, showing the detector's effectiveness in on-site applications. The detector enabled simultaneous measurement of radioactivity and energy spectrum of individual particles, facilitating rapid discrimination between Pu and Np. The imaging detector has potential for enhancing on-site detection of alpha nuclides in nuclear facilities, aiding in decontamination efforts and environmental monitoring.

Development of contamination detection system combined with various remote devices

Morishita, Yuki; Miyamura, Hiroko; Sato, Yuki; Oura, Masatoshi*

Radiation Measurements, 171, p.107064_1 - 107064_7, 2024/02

https://doi.org/10.1016/j.radmeas.2024.107064

The detection of alpha and beta contamination locations is important for decontaminating nuclear facilities. In the high radiation dose rate environment at the decommissioning sites, the contamination measurement by the workers is not effective. Thus, we developed a remote automatic contamination measurement system using a new scintillator-based detector. A 50 mm 100-m-thick YAlO(Ce)(YAP:Ce) scintillator was coupled with a flat panel-type multianode photomultiplier tube. The detector was installed downwards at the bottom of a robot. It has an energy measurement capability, and the energy measurement could discriminate the alpha particles from the beta and Rn alpha particles. With the energy information, alpha and beta particles could be identified and mapped simultaneously. In addition, a slow-moving robot could be used to obtain statistically sufficient counts in a single run measurement, allowing the evaluation of surface contamination density using only alpha particles. The remote automatic contamination measurement system will be useful in visualizing the contamination distribution in environments that are inaccessible to workers.

Development of a portable -ray dust monitor for highly-concentrated airborne contaminants

Sagawa, Naoki; Fujisawa, Makoto; Hosomi, Kenji; Morishita, Yuki; Takada, Chie

Hoken Butsuri (Internet), 58(3), p.135 - 140, 2023/11

https://doi.org/10.5453/jhps.58.135

Radioactivity concentrations of airborne dust are important measurements because they are used to protect workers from intakes and to assess internal exposure doses. Therefore, we developed a portable -ray dust monitor by using an ultra-thin plastic scintillator, which is designed for continuous monitoring of highly-concentrated airborne contaminants ( 10 Bq/cm, equivalent to 30 times larger than the derived air concentration of Sr) such as a decommissioning work in the Fukushima Daiichi Nuclear Power Plant. From the performance test results, it is evaluated that the developed portable -ray dust monitor is functional in continuous monitoring with an airborne concentration of 1 Bq/cm.

Development of a method of evaluating PuO particle diameters using an alpha-particle imaging detector

Morishita, Yuki; Sagawa, Naoki; Takada, Chie; Momose, Takumaro; Takasaki, Koji

Radiation Protection Dosimetry, 199(13), p.1376 - 1383, 2023/08

https://doi.org/10.1093/rpd/ncad186

It is very important to evaluate the diameters (activity median aerodynamic diameter) of Plutonium dioxide (PuO) particles for internal exposure dose evaluation. In this study, a method of evaluating PuO particle diameters using an alpha-particle imaging detector was developed. PuO particles with different diameters were modeled by Monte Carlo simulation, and the change in the shape of the energy spectrum for each particle diameter was evaluated. Two different patterns were modeled, namely, the case of PuO and the case of PuO (including isotopic composition of Pu). Multiple regression analysis was performed to determine the PuO particle diameter from the obtained parameters. The simulated diameters and the diameters obtained with the regression model were in good agreement. The advantage of using the alpha-particle imaging detector is to measure the alpha energy spectrum for individual particle, and this allows accurate measurement of particle diameter distribution.

End-to-end simulations and error studies of the J-PARC muon linac

Takeuchi, Yusuke*; Tojo, Junji*; Yamanaka, T.*; Nakazawa, Yuga*; Iinuma, Hiromi*; Kondo, Yasuhiro; Kitamura, Ryo; Morishita, Takatoshi; Cicek, E.*; Ego, Hiroyasu*; et al.

Proceedings of 31st International Linear Accelerator Conference (LINAC 2022) (Internet), p.562 - 564, 2022/10

https://doi.org/10.18429/JACoW-LINAC2022-TUPORI08

A muon linac is under development for future muon g-2/EDM experiments at J-PARC. The linac provides a 212 MeV muon beam to an MRI-type compact storage ring. After the initial acceleration using the electrostatic field created by mesh and cylindrical electrodes, the muons are accelerated using four types of radio-frequency accelerators. To validate the linac design as a whole, end-to-end simulations were performed using General Particle Tracer. In addition, error studies were performed to investigate the effects on beam and spin dynamics of various errors in the accelerator components and input beam distribution. This paper describes the results of the end-to-end simulations and error studies.

The Muon linac project at J-PARC

Kondo, Yasuhiro; Kitamura, Ryo; Fuwa, Yasuhiro; Morishita, Takatoshi; Moriya, Katsuhiro; Takayanagi, Tomohiro; Otani, Masashi*; Cicek, E.*; Ego, Hiroyasu*; Fukao, Yoshinori*; et al.

Proceedings of 31st International Linear Accelerator Conference (LINAC 2022) (Internet), p.636 - 641, 2022/09

https://doi.org/10.18429/JACoW-LINAC2022-WE1AA05

The muon linac project for the precise measurement of the muon anomalous magnetic and electric dipole moments, which is currently one of the hottest issues of the elementary particle physics, is in progress at J-PARC. The muons from the J-PARC muon facility are once cooled to room temperature, then accelerated up to 212 MeV with a normalized emittance of 1.5 mm mrad and a momentum spread of 0.1%. Four types of accelerating structures are adopted to obtain the efficient acceleration with a wide beta range from 0.01 to 0.94. The project is moving into the construction phase. We already demonstrated the re-acceleration scheme of the decelerated muons using a 324-MHz RFQ in 2017. The high-power test of the 324-MHz Interdigital H-mode (IH) DTL using a prototype cavity was performed in 2021. The fabrication of the first module of 14 modules of the 1296-MHz Disk and Washer (DAW) CCL will be done to confirm the production process. Moreover, the final design of the travelling wave accelerating structure for the high beta region is also proceeding. In this paper, the recent progress toward the realization of the world first muon linac will be presented.

Fabrication and low-power test of disk-and-washer cavity for muon acceleration

Takeuchi, Yusuke*; Tojo, Junji*; Nakazawa, Yuga*; Kondo, Yasuhiro; Kitamura, Ryo; Morishita, Takatoshi; Cicek, E.*; Ego, Hiroyasu*; Futatsukawa, Kenta*; Kawamura, Naritoshi*; et al.

Proceedings of 13th International Particle Accelerator Conference (IPAC 22) (Internet), p.1534 - 1537, 2022/06

https://doi.org/doi:10.18429/JACoW-IPAC2022-TUPOMS046

The muon g-2/EDM experiment is under preparation at Japan Proton Accelerator Research Complex (J-PARC), and the muon linear accelerator for the experiment is being developed. A Disk-and-Washer (DAW) cavity will be used for the medium-velocity part of the accelerator, and muons will be accelerated from = = 0.3 to 0.7 with the operating frequency of 1.296 GHz. Machining, brazing, and low-power measurements of a prototype cell reflecting the design of the first tank of DAW were performed to identify fabrication problems. Several problems were identified, such as misalignment of washers during brazing, and some measures will be taken in the actual tank fabrication. In this paper, the results of the prototype cell fabrication will be reported.

Stabilization treatment of Pu-bearing organic materials

Morishita, Kazuki; Sato, Takumi; Onishi, Takashi; Seki, Takayuki*; Sekine, Shinichi*; Okitsu, Yuichi*

JAEA-Technology 2021-024, 27 Pages, 2021/10

JAEA-Technology-2021-024.pdf:2.41MB

In the case of Plutonium (Pu)-bearing organic materials, organic materials are decomposed by alpha rays emitted mainly from Pu to generate hydrogen gas and other substances. Therefore, to safely store Pu-bearing organic materials for an extended period of time, organic materials must be eliminated. In addition, carbide and nitride fuels must be converted into oxides for safe storage in order to prevent the exothermal reaction of these fuels with oxygen/moisture in air. A survey of the literature on the stabilization treatment of Pu-bearing organic materials confirmed that organic materials can be decomposed and removed by heating at 950 C (1223.15 K) or greater in air. Furthermore, based on the calculated thermodynamic parameters of oxidation reaction of carbide and nitride fuels in air, it was estimated that these fuels would be oxidized in air at 950 C because the equilibrium oxygen partial pressure in the oxidation reaction at 950 C was lower than 2.110 Pa (oxygen partial pressure in air). Therefore, it was decided to stabilize Pu-bearing organic materials by heating at 950 C in air to remove the organic materials and oxidize the carbide and nitride fuels. As a mock-up test to remove the organic materials, thin sheets of epoxy resin were heated in air. The changes in appearance and weight before and after heating in air showed that organic materials can be removed. After the mock-up test, Pu-bearing organic materials were also stabilized by heating in the similar condition.

Plutonium dioxide particle imaging using a high-resolution alpha imager for radiation protection

Morishita, Yuki; Kurosawa, Shunsuke*; Yamaji, Akihiro*; Hayashi, Masateru*; Sasano, Makoto*; Makita, Taisuke*; Azuma, Tetsushi*

Scientific Reports (Internet), 11(1), p.5948_1 - 5948_11, 2021/03

AA2020-0761.pdf:1.59MB

https://doi.org/10.1038/s41598-021-84515-z

The internal exposure of workers who inhale plutonium dioxide particles in nuclear facilities is a crucial matter for human protection from radiation. To determine the activity median aerodynamic diameter values at the working sites of nuclear facilities in real time, we developed a high-resolution alpha imager using a ZnS(Ag) scintillator sheet, an optical microscope, and an electron-multiplying charge-coupled device camera. Then, we designed and applied a setup to measure a plutonium dioxide particle and identify the locations of the individual alpha particles in real time. Employing a Gaussian fitting, we evaluated the average spatial resolution of the multiple alpha particles was evaluated to be 16.2 umFWHM with a zoom range of 5 x. Also, the spatial resolution for the plutonium dioxide particle was 302.7 umFWHM due to the distance between the plutonium dioxide particle and the ZnS(Ag) scintillator. The influence of beta particles was negligible, and alpha particles were discernible in the alpha-beta particle contamination. The equivalent volume diameter of the plutonium dioxide particle was calculated from the measured count rate. These results indicate that the developed alpha imager is effective in the plutonium dioxide particle measurements at the working sites of nuclear facilities for internal exposure dose evaluation.