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論文

Improvement of detection limit in differential die-away analysis system for nuclear non-proliferation and nuclear security

大図 章; 前田 亮; 米田 政夫; 藤 暢輔

Proceedings of 2019 IEEE Nuclear Science Symposium and Medical Imaging Conference (IEEE NSS/MIC 2019), Vol.1, p.101 - 104, 2020/08

In the fields of safeguards, nuclear non-proliferation, and nuclear security, non-destructive analysis (NDA) techniques useful for highly radioactive nuclear materials (NMs) are not established yet because there are so many technical difficulties to measure the amount of the highly radioactive NMs. A novel NDA system with a pulsed neutron source as the method for determining the composition of mixed NMs has been developing in the Japan Atomic Energy Agency. In the NDA system, a differential die-away analysis (DDA) technique is used to quantify the amount of fissile materials. The detection limit of fissile materials in DDA system is determined by the signal to noise ratio in fast neutron counting. A method to reduce the noise signal by using neutron absorber (B$$_{4}$$C rubber) sheets mounted on the inner entire surface in the sample cavity is proposed. The effect of the sheets on the reduction of noise signal in the fast neutron counting was investigated in both experimental test and simulation. The experimental results show that it is possible to detect a nuclear fissile material ($$^{239}$$Pu) of as low as 1 mg in a vial bottle when the absorber sheets with a thickness of 3 mm is used. This paper also presents comparison between experimental data and simulation results.

口頭

System development and challenges for delayed gamma-ray nondestructive assay in safeguard verification of nuclear material

Rossi, F.; Rodriguez, D.; 瀬谷 道夫; 高橋 時音; 小泉 光生; Abbas, K.*; Crochemore, J.-M.*; Pedersen, B.*; Bogucarska, T.*; Varasano, G.*; et al.

no journal, , 

New active-interrogation nondestructive assay techniques are needed for safeguard purpose. They can be used for the quantification of the fissile composition in high radioactivity nuclear material samples. One of the techniques under evaluation by the Japan Atomic Energy Agency together with the European Commission Joint Research Centre is delayed gamma-ray spectroscopy. It utilizes a combination of high rate neutron sources and moderation to thermal energy to induce fission in the fissile nuclides. This will allow enhancing the amount of observable coming from the fission of the fissile compared with the fertile nuclides that are usually more abundant in the sample. Analyzing the peaks ratios of gamma-rays with energy above 3 MeV emitted by the short lived fission products produced in the sample, it is possible to verify the initial composition of the fissile nuclides. We are currently designing and testing several different systems with the goal to design a practical and compact system that can be installed in current reprocessing facilities. In particular, this paper describes the different systems currently tested focusing on the different neutron source and moderator material and geometry as well as different gamma-ray detectors. We will also show the new neutron and gamma-ray detector systems we will implement for future test and development. This work is supported by the subsidy for the "promotion of strengthening nuclear security and the like" from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan.

口頭

Radon measurements in a small chamber using compact organic scintillator-based alpha/beta spectrometer

森下 祐樹; Ye, Y.*; Mata, L.*; Pozzi, S.*; Kearfott, K.*

no journal, , 

コンパクトな有機シンチレータベースの$$alpha beta$$スペクトロメータを開発し、ラドン測定を行った。pulse shape discrimination技術を使って$$alpha$$線と$$beta$$線のスペクトルを同時に得ることができた。$$alpha$$スペクトルを見るとラドン子孫核種である$$^{218}$$Poと$$^{214}$$Poのピークが確認された。市販のラドン測定器とも直線的な関係を示した。開発したスペクトロメータは厚みも薄く、小型である。そのため感度は低いが、複数並べることで感度を向上させることも可能である。そのため、開発した$$alpha beta$$スペクトロメータは、新しいラドン検出器としての可能性を有している。

口頭

Detection of alpha particle emitters originating from nuclear fuel inside reactor building of Fukushima Daiichi Nuclear Power Station

森下 祐樹; 鳥居 建男; 宇佐美 博士; 菊地 弘幸*; 宇津木 弥*; 高平 史郎*

no journal, , 

福島第一原子力発電所の原子炉建屋で採取されたスミヤ試料上の$$alpha$$核種を$$alpha$$線イメージング検出器で測定した。極薄のGAGGシンチレータとSiPMアレーで検出器を構成した。$$alpha$$スペクトルは5-6MeV領域に確認され$$^{238}$$Puのエネルギーと一致した。$$gamma$$線スペクトロメトリで$$^{241}$$Amのピークも確認できた。これらの測定結果から福島第一原子力発電所の$$alpha$$核種として$$^{238}$$Puや$$^{241}$$Amが存在することを現場での測定により明らかにした。

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