Effect of neutron beam properties on dose distributions in a water phantom for boron neutron capture therapy

石川 諒尚; 田中 浩基*; 中村 哲志*; 熊田 博明*; 櫻井 良憲*; 渡辺 賢一*; 吉橋 幸子*; 棚上 裕生*; 瓜谷 章*; 鬼柳 善明*

Journal of Radiation Research (Internet), 11 Pages, 2024/10

https://doi.org/10.1093/jrr/rrae076

From the viewpoints of the advantage depths (ADs), peak tumor dose, and skin dose, we evaluated the effect of neutron beam properties, namely, the ratio between thermal and epithermal neutron fluxes (thermal/epithermal ratio), fast neutron component, and -ray component on the dose distribution. Several parameter surveys were conducted with respect to the beam properties of neutron sources for boron neutron capture therapy assuming boronophenylalanine as the boron agent using our dose calculation tool, called SiDE. The ADs decreased by 3% at a thermal/epithermal ratio of 20% - 30% compared with the current recommendation of . The skin dose increased with the increasing thermal/epithermal ratio, reaching a restricted value of 14 Gy-eq at a thermal/epithermal ratio of . The fast neutron component was modified using two different models, namely, the "linear model," in which the fast neutron intensity decreases log-linearly with the increasing neutron energy, and the "moderator thickness (MT) model," in which the fast neutron component is varied by adjusting the moderator thickness in a virtual beam shaping assembly. Although a higher fast neutron component indicated a higher skin dose, the increment was at a fast neutron component of Gy cm for both models. Furthermore, in the MT model, the epithermal neutron intensity was higher at a fast neutron component of Gy cm compared with the current recommendation of Gy cm. The -ray component also caused no significant disadvantages up to several times larger compared with the current recommendation.

A New application technique of a position-sensitive liquid light guide Cerenkov counter for the simultaneous position detection of Sr/Y and Cs radioactivity

寺阪 祐太; 瓜谷 章*

Nuclear Instruments and Methods in Physics Research A, 1049, p.168071_1 - 168071_7, 2023/04

https://doi.org/10.1016/j.nima.2023.168071

A new application of a position-sensitive liquid light guide Cerenkov counter for the simultaneous position detection of Sr/Y and Cs radioactivity in a gamma-ray-dominant environment is proposed. -emitting Sr/Y and -emitting Cs radioactive point sources were measured using a position-sensitive liquid light guide based on the time-of-flight (TOF) method. We found a clear difference in the count rate ratio between the source position peak and reflection peak of the position histogram. Moreover, simultaneous measurements of the radioactive point sources were performed. The results suggest that the source position and activity of Sr/Y and Cs can be simultaneously determined based on the count rate ratio of the source position peak and the reflection peak.

光ファイバを用いた新方式片側読み出し型放射線分布測定法に関する基礎研究

寺阪 祐太; 渡辺 賢一*; 瓜谷 章*

放射線(インターネット), 47(3), p.89 - 96, 2022/10

We developed a novel single-end readout type position-sensitive optical fiber radiation sensor. This sensor measures the radiation intensity distribution along the fiber with light readout only from single end of the optical fiber. To estimate the radiation intensity distribution, we analyzed the wavelength spectrum output at single end of the fiber, which contains information about the transmission distance of light inside the fiber. Based on the unfolding of the wavelength spectrum, the radiation intensity distribution along the fiber could be estimated. The effects of wavelength channel selection and signal-to-noise ratio of the wavelength spectrum on radiation distribution estimation were evaluated. In addition, we performed that our optical fiber sensor could estimate the radiation intensity distribution under the dose rate of 3 Gy/h. The dose rate detection limit was estimated to be 21 mGy/h for the irradiation range of 20 cm.

First demonstration of a novel single-end readout type position-sensitive optical fiber radiation sensor based on wavelength-resolved photon counting

寺阪 祐太; 渡辺 賢一*; 瓜谷 章*

Nuclear Instruments and Methods in Physics Research A, 1034, p.166793_1 - 166793_6, 2022/07

https://doi.org/10.1016/j.nima.2022.166793

In this study, a single-end readout type position-sensitive optical fiber radiation sensor was developed. Using the wavelength dependency of light attenuation inside the optical fiber, the incident position of radiation at the fiber can be estimated reversely. Instead of a spectrometer, we employed bandpass filters and photon-counting head as a photodetector to improve detection efficiency. The detection efficiency of a 10 m long plastic scintillation fiber at the 5 m position from the readout end was evaluated to be in the range of 0.08-0.12 % for 662 keV gamma-rays from Cs and 2.6-3.9 % for beta-rays from Sr/Y when a bandpass filter transmitting photons with a wavelength of 500 nm was used. A basic measurement test of radiation intensity distribution was conducted using a Sr/Y radioactive point source. A field test was also performed at the difficult-to-return zone in Fukushima Prefecture, and the estimated dose rate distribution roughly agreed with the survey meter measurement.

High-spatial-resolution measurement of magnetization distribution using polarized neutron imaging

笹田 星児*; 廣井 孝介; 小山内 健太*; 篠原 武尚; Watanabe, K.*; 瓜谷 章*

Japanese Journal of Applied Physics, 60(12), p.126003_1 - 126003_6, 2021/12

https://doi.org/10.35848/1347-4065/ac3524

The evaluation of the magnetization distribution inside a bulk magnet is important for ensuring the performance of automotive motors because it strongly depends on the quality of magnetization inside the permanent magnet. In the conventional destructive method, it is difficult to accurately measure the magnetization with a high spatial resolution. The polarized neutron imaging technique can be used to visualize the distribution of the magnetic flux density inside a magnet nondestructively. In this study, we demonstrated the imaging of the magnetization distribution using polarized neutrons in an anisotropic ferrite magnet sample. The 2D distribution of the magnetization was experimentally obtained by polarized neutron imaging with a high spatial resolution of less than 1 mm. Furthermore, the validity of the results was confirmed by comparing them with those obtained using the conventional destructive method.

Evaluation of a one-dimensional position-sensitive quartz optical fiber sensor based on the time-of-flight method for high radiation dose rate applications

寺阪 祐太; 渡辺 賢一*; 瓜谷 章*

Nuclear Instruments and Methods in Physics Research A, 996, p.165151_1 - 165151_8, 2021/04

https://doi.org/10.1016/j.nima.2021.165151

福島第一原子力発電所建屋内における放射線分布測定を目的として、小口径石英光ファイバーの一次元位置敏感型センサーとしての基礎評価を行った。本センサーは光ファイバーと放射線の相互作用により発生するチェレンコフ光の飛行時間情報から放射線の入射位置を決定する。プラスチックシンチレーション光ファイバーを用いた従来のセンサーと比較して、石英光ファイバーは位置分解能がより優れることが分かった。これは、チェレンコフ光の発光寿命が短いことによりタイミング特性が向上したためと考えられた。加えて、本センサーの高放射線環境下での動作特性について、20mSv/hまでの出力線形性及び積算1kGyまでの耐放射線特性を評価した。

Pulsed neutron imaging based crystallographic structure study of a Japanese sword made by Sukemasa in the Muromachi period

及川 健一; 鬼柳 善明*; 佐藤 博隆*; 大前 良磨*; Pham, A.*; 渡辺 賢一*; 松本 吉弘*; 篠原 武尚; 甲斐 哲也; Harjo, S.; et al.

Materials Research Proceedings, Vol.15, p.207 - 213, 2020/02

https://doi.org/10.21741/9781644900574-32

Japanese swords are very attractive not only as a work of art but also a metallurgical point of view. Since Japanese vintage swords became valuable, it is indispensable to establish non-destructive analysis method to identify some peculiar characteristics. Bragg edge imaging gives real-space distributions of bulk information in a crystalline material as well as neutron tomography. In this work, we investigated crystallographic information of a Japanese sword made by Sukemasa in Izumi province in the first quarter of the 16th century. The experiments have been performed at RADEN at J-PARC. The Sukemasa sword was measured with a counting-type 2D detector and with a CCD camera. We are now analyzing the measured 2D-transmission spectra using RITS code to obtain spatial distribution of the crystallite size, the texture variation, the d110 shift and its broadening. Complementary data analysis using white beam tomography is also on going. Detailed analysis results will be presented.

Construction of 144, 565 keV and 5.0 MeV monoenergetic neutron calibration fields at JAERI

谷村 嘉彦; 吉澤 道夫; 三枝 純; 藤井 克年; 清水 滋; 吉田 真; 柴田 泰成*; 瓜谷 章*; 工藤 勝久*

Radiation Protection Dosimetry, 110(1-4), p.85 - 89, 2004/09

https://doi.org/10.1093/rpd/nch197

日本原子力研究所放射線標準施設棟では4MVペレトロン型加速器を利用した単色中性子校正場を開発している。中性子スペクトルの評価を行い、中性子フルエンスに関するトレーサビリティを確立することにより144keV,565keV,5.0MeVの中性子校正場が構築された。

光ファイバーを用いた高信頼性・高機能放射線モニタの開発研究(先行基礎工学研究)

辻村 憲雄; 吉田 忠義; 河原林 順*; 水野 良治*; 中 亮太郎*; 瓜谷 章*; 渡辺 賢一*

JNC TY8400 2003-010, 46 Pages, 2003/03

JNC-TY8400-2003-010.pdf:1.36MB

通常光ファイバーを利用した広域の放射線分布を連続的に測定することができる放射線検出システムを開発した。光減衰の小さい通常光ファイバーを使用することにより、従来使用されてきたプラスチックシンチレーションファイバーに比べ、測定可能範囲が約100mへと約2桁伸ばすことができた。

Direct measurement of gaseous activities by diffusion-in long proportional counter method

吉田 真; 山本 敏生*; Wu, Y.*; 新谷 徹*; 瓜谷 章*; 森 千鶴夫*

Nuclear Instruments and Methods in Physics Research A, 330, p.158 - 164, 1993/00

https://doi.org/10.1016/0168-9002(93)91318-H

放射性ガスの放射能を長軸比例計数管内拡散法により直接測定を行なう研究をした。この方法は、比例計数管に放射性ガスを封入して放射能絶対測定をする上で問題となる端効果を除く方法としてきわめて有効である。この測定の際必要な基礎データをArの計数管内挙動をモニタリングすることにより収集し評価した。その結果、十分な精度で放射能の決定が行なえることがわかった。また、端効果とともに重要な補正である壁効果についても実験及び計算により評価した。