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論文

Activation measurement for thermal-neutron capture cross-section of Cesium-135

中村 詔司; 木村 敦; 岩本 修; 芝原 雄司*; 上原 章寛*; 藤井 俊行*

KURNS Progress Report 2018, P. 106, 2019/08

核変換による高レベル放射性廃棄物の大幅な低減化、資源化を目指した革新的研究開発推進プログラム(ImPACT)において、長寿命核分裂生成核種$$^{135}$$Csの中性子捕獲断面積測定研究を京都大学複合原子力科学研究所にて行った。本論文は、京大原子炉(KUR)を用いた$$^{135}$$Csの熱中性子捕獲断面積の測定について報告するものである。

論文

Measurements of the $$^{243}$$Am neutron capture and total cross sections with ANNRI at J-PARC

木村 敦; 中村 詔司; 寺田 和司*; 中尾 太郎*; 水山 一仁*; 岩本 信之; 岩本 修; 原田 秀郎; 片渕 竜也*; 井頭 政之*; et al.

Journal of Nuclear Science and Technology, 56(6), p.479 - 492, 2019/06

Neutron total and capture cross sections of $$^{243}$$Am have been measured in Accurate Neutron Nucleus Reaction measurement Instrument at Materials and Life Science Experimental Facility of Japan Proton Accelerator Research Complex with a neutron TOF method. The neutron capture cross section in the energy region from 10 meV to 100 eV was determined using an array of Ge detectors. Three samples with different activities were used for measurements of the capture cross section. The neutron total cross section in the energy region from 4 meV to 100 eV was measured using Li-glass detectors. Derived cross-section value at neutron energy of 0.0253 eV is 87.7$$pm$$5.4 b for the capture cross section and 101$$pm$$11 b for the total cross section.

論文

Measurements of thermal-neutron capture cross-section and resonance integral of neptunium-237

中村 詔司; 北谷 文人; 木村 敦; 上原 章寛*; 藤井 俊行*

Journal of Nuclear Science and Technology, 56(6), p.493 - 502, 2019/06

放射化法により$$^{237}$$Np(n,$$gamma$$)$$^{238}$$Np反応の熱中性子捕獲断面積($$sigma_{0}$$)及び共鳴積分(I$$_{0}$$)を測定した。$$^{237}$$Npの0.489eVにある第一共鳴に注意を払い、カドミウム差法において、ガドリニウムフィルタを用いて、カットオフエネルギーを0.133eVに設定して$$sigma_{0}$$を測定した。ネプツニウム237試料を、京都大学複合原子力科学研究所の研究炉にて照射した。照射位置における熱中性子束、及び熱外ウェストコット因子を決定するために、金合金線モニタ、及びコバルト合金線モニタも一緒に照射した。照射したネプツニウム237試料及びモニタ試料の生成放射能を、ガンマ線分光により測定した。ウェストコットの理論に基づき、$$sigma_{0}$$とI$$_{0}$$を、それぞれと186.9$$pm$$6.2 barn、及び1009$$pm$$90 barnと導出した。

論文

Measurement of $$^{73}$$Ge(n,$$gamma$$) cross sections and implications for stellar nucleosynthesis

Lederer-Woods, C.*; Battino, U.*; Ferreira, P.*; Gawlik, A.*; 木村 敦; n_TOF Collaboration*; 他128名*

Physics Letters B, 790, p.458 - 465, 2019/03

$$^{73}Ge(n,gamma)$$ cross sections were measured at the neutron time-of-flight facility n_TOF at CERN up to neutron energies of 300 keV, providing for the first time experimental data above 8 keV. Results indicate that the stellar cross section at $$kT$$ =30 keV is 1.5 to 1.7 times higher than most theoretical predictions. The new cross sections result in a substantial decrease of $$^{73}$$Ge produced in stars, which would explain the low isotopic abundance of $$^{73}$$Ge in the solar system.

論文

Gamma-ray spectrum from thermal neutron capture on gadolinium-157

萩原 開人*; 矢野 孝臣*; Das, P. K.*; Lorenz, S.*; 王 岩*; 作田 誠*; 木村 敦; 中村 詔司; 岩本 信之; 原田 秀郎; et al.

Progress of Theoretical and Experimental Physics (Internet), 2019(2), p.023D01_1 - 023D01_26, 2019/02

We have measured the $$gamma$$-ray energy spectrum from the thermal neutron capture, $$^{157}Gd(n,gamma)^{158}Gd$$, on an enriched $$^{157}$$Gd target ($$Gd_2O_3$$) in the energy range from 0.11 MeV up to about 8 MeV. The target was placed inside the germanium spectrometer of the ANNRI detector at J-PARC and exposed to a neutron beam from the Japan Spallation Neutron Source (JSNS). Radioactive sources ($$^{60}$$Co, $$^{137}$$Cs, and $$^{152}$$Eu) and the reaction $$^{35}Cl(n,gamma)$$ were used to determine the spectrometer's detection efficiency for $$gamma$$ rays at energies from 0.3 to 8.5 MeV. Using a Geant4-based Monte Carlo simulation of the detector and based on our data, we have developed a model to describe the $$gamma$$-ray spectrum from the thermal $$^{157}Gd(n,gamma)^{158}Gd$$ reaction. While we include the strength information of 15 prominent peaks above 5 MeV and associated peaks below 1.6 MeV from our data directly into the model, we rely on the theoretical inputs of nuclear level density and the photon strength function of $$^{158}$$Gd to describe the continuum $$gamma$$-ray spectrum from the $$^{157}Gd(n,gamma)^{158}Gd$$ reaction. The results of the comparison between the observed $$gamma$$-ray spectra from the reaction and the model are reported in detail.

論文

Cross section measurements of $$^{155,157}$$Gd(n,$$gamma$$) induced by thermal and epithermal neutrons

Mastromarco, M.*; Manna, A.*; Aberle, O.*; Andrzejewski, J.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他116名*

European Physical Journal A, 55(1), p.9_1 - 9_20, 2019/01

Neutron capture cross section measurements on $$^{155}$$Gd and $$^{157}$$Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements were carried out in the n TOF experimental area EAR1, at 185m from the neutron source, with an array of 4 C$$_6$$D$$_6$$ liquid scintillation detectors. At a neutron kinetic energy of 0.0253eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for $$^{155}$$Gd and $$^{157}$$Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181eV and 307eV, respectively for $$^{155}$$Gd and $$^{157}$$Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of 2.01(28) $$times$$ 10$$^{-4}$$ and 2.17(41) $$times$$ 10$$^{-4}$$; average total radiative width of 106.8(14)meV and 101.1(20)meV and s-wave resonance spacing 1.6(2)eV and 4.8(5)eV for n + $$^{155}$$Gd and n + $$^{157}$$Gd systems, respectively.

論文

Measurements of gamma-ray emission probabilities in the decay of americium-244g

中村 詔司; 寺田 和司*; 木村 敦; 中尾 太郎*; 岩本 修; 原田 秀郎; 上原 章寛*; 高宮 幸一*; 藤井 俊行*

Journal of Nuclear Science and Technology, 56(1), p.123 - 129, 2019/01

 パーセンタイル:100(Nuclear Science & Technology)

$$gamma$$線計測により同位体を定量したり、断面積を求める際に、正確な$$gamma$$線放出率のデータが、必要になってくる。$$^{243}$$Amは、重要なマイナーアクチノイド核種の一つであり、中性子捕獲後に$$^{244}$$Amを生成する。$$^{244}$$Amの基底状態から放出される744-keV$$gamma$$線は66%と比較的大きな$$gamma$$線放出率を持つけれども、その誤差は29%と大きい。$$gamma$$線放出率の誤差は、放射化法による中性子捕獲断面積測定において、系統誤差の主要因となる。そこで、放射化法と$$^{244}$$Cmのレベルを調べることにより、$$gamma$$線放出率を測定した。本研究により、744-keV$$gamma$$線の放出率を、66.5$$pm$$1.1%と、相対誤差29%から2%に低減して導出することができた。

論文

Progress of neutron-capture cross-section measurements promoted by ImPACT project at ANNRI in MLF of J-PARC

中村 詔司; 木村 敦; Hales, B. P.; 岩本 修; 芝原 雄司*; 上原 章寛*; 藤井 俊行*

JAEA-Conf 2018-001, p.199 - 203, 2018/12

ImPACTプロジェクトにおいて、長寿命核分裂生成物の中の$$^{135}$$Csについて、その中性子捕獲断面積測定をJ-PARCのMLF施設内に設置されているANNRI装置を用いて進めている。将来の測定のために$$^{79}$$Seサンプルの整備可能性の検討と並行して、安定Se同位体核種について、それらの中性子捕獲断面積測定も進めている。本発表では、放射性$$^{135}$$Cs試料の整備とそれを用いた照射試験、安定Se同位体の断面積測定などについて報告する。

論文

Analysis of $$^{135}$$Cs/$$^{137}$$Cs isotopic ratio for samples used for neutron capture cross section measurement project by thermal ionization mass spectrometry

芝原 雄司*; 上原 章寛*; 藤井 俊行*; 中村 詔司; 木村 敦; Hales, B. P.; 岩本 修

JAEA-Conf 2018-001, p.205 - 210, 2018/12

ImPACT事業の中性子捕獲断面積研究において、$$^{135}$$Cs中性子捕獲断面積測定に使用する試料として$$^{137}$$Cs標準溶液中に含まれる$$^{135}$$Csの利用を考えた。$$^{135}$$Cs試料を定量するためには、$$^{135}$$Csと$$^{137}$$Csの同位体比を高精度で分析する必要がある。そこで、熱イオン化質量分析器(TIMS)を用いて、最初のサンプルとして$$^{137}$$Cs標準溶液の質量分析試験を行なった。分析試験の結果、わずか10Bq(pgオーダー)の$$^{137}$$Cs標準溶液でも$$^{135}$$Csと$$^{137}$$Csの同位体比を0.5%の高精度で導出することができた。

論文

Measurements of neutron total and capture cross sections of $$^{241}$$Am with ANNRI at J-PARC

寺田 和司*; 木村 敦; 中尾 太郎*; 中村 詔司; 水山 一仁*; 岩本 信之; 岩本 修; 原田 秀郎; 片渕 竜也*; 井頭 政之*; et al.

Journal of Nuclear Science and Technology, 55(10), p.1198 - 1211, 2018/10

 被引用回数:1 パーセンタイル:38.14(Nuclear Science & Technology)

Neutron total and capture cross sections of $$^{241}$$Am have been measured with a new data acquisition system and a new neutron transmission measurement system installed in Accurate Neutron Nucleus Reaction measurement Instrument (ANNRI) at Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). The neutron total cross sections of $$^{241}$$Am were determined by using a neutron time-of-flight method in the neutron energy region from 4 meV to 2 eV. The thermal total cross section of $$^{241}$$Am was derived with an uncertainty of 2.9%. A pulse-height weighting technique was applied to determine neutron capture yields of $$^{241}$$Am. The neutron capture cross sections were determined by the time-of-flight method in the neutron energy region from the thermal to 100 eV, and the thermal capture cross section was obtained with an uncertainty of 4.1%. The evaluation data of JENDL-4.0 and JEFF-3.2 were compared with the present results.

論文

Experimental validation of the brightness distribution on the surfaces of coupled and decoupled moderators composed of 99.8% parahydrogen at the J-PARC pulsed spallation neutron source

原田 正英; 勅使河原 誠; 大井 元貴; Klinkby, E.*; Zanini, L.*; Batkov, K.*; 及川 健一; 藤 暢輔; 木村 敦; 池田 裕二郎

Nuclear Instruments and Methods in Physics Research A, 903, p.38 - 45, 2018/09

 被引用回数:3 パーセンタイル:7.87(Instruments & Instrumentation)

At the J-PARC pulsed spallation neutron source, liquid hydrogen moderators composed of 99.8% parahydrogen associated with light-water premoderator have been providing high intensity cold and thermal neutron beams. In the design stage, simulations have shown not only high total neutron intensity in the coupled moderator but also a local neutron-brightness increase at the edges. The edge-effect-brightness increase is also exploited in the design of the European Spallation Source (ESS) moderators, which are based on 99.8% parahydrogen, but thin (thickness: 3 cm) to enhance the neutron brightness. In this study, the spatial distribution of the neutron brightness at the surface of the coupled moderator in the J-PARC pulsed spallation neutron source was directly measured with the pinhole geometry to validate the calculated edge-brightness enhancement. The brightness distribution at the moderator surface was clearly observed as predicted by a Monte Carlo simulation, proving the validity of the simulation tools used in the design-optimization process of the J-PARC and ESS moderator.

論文

$$^7$$Be(n,p)$$^7$$Li reaction and the cosmological lithium problem; Measurement of the cross section in a wide energy range at n_TOF at CERN

Damone, L.*; Barbagallo, M.*; Mastromarco, M.*; Cosentino, L.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他152名*

Physical Review Letters, 121(4), p.042701_1 - 042701_7, 2018/07

We report on the measurement of the $$^7$$Be(n,p)$$^7$$Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a $$^7$$Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal $$^7$$Li(p,n)$$^7$$Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near threshold neutron production in the p+$$^7$$Li reaction is also discussed.

論文

第30回NEA核データ評価国際協力ワーキングパーティ(WPEC)会合報告

岩本 修; 岩本 信之; 木村 敦; 横山 賢治; 多田 健一

核データニュース(インターネット), (120), p.35 - 46, 2018/06

経済開発協力機構原子力機関(OECD/NEA)の第30回核データ評価国際ワーキングパーティ(WPEC)会合が、2018年5月14日から18日の日程でOECD本部で開催された。期間中に開催されたWPEC本会合、エキスパートグループ会合及びサブグループ会合について報告する。

論文

Radiation-induced degradation of aqueous 2-chlorophenol assisted by zeolites

熊谷 友多; 木村 敦*; 田口 光正*; 渡邉 雅之

Journal of Radioanalytical and Nuclear Chemistry, 316(1), p.341 - 348, 2018/04

 パーセンタイル:100(Chemistry, Analytical)

放射線を利用した水環境汚染物質の分解処理をゼオライトによる固相抽出を用いて効率化する可能性を探索するため、2-クロロフェノール(2-ClPh)をモデル物質としてゼオライト共存下での放射線誘起反応を研究した。3種のゼオライトを比較した結果、Si/Al比率の高いゼオライト(HMOR)を用いることで2-ClPhの放射線による分解反応を効率化できることを明らかにした。HMORは疎水性を示すゼオライトであり、水溶液中の2-ClPhに対して優れた吸着能を示した。この吸着能を利用してHMORに2-ClPhを濃縮してから$$gamma$$線を照射することで、2-ClPhの脱塩素反応が高効率で進むことが分かった。この固相抽出による反応効率の向上は、水溶液を10倍濃縮することに相当した。これは、2-ClPhが高濃度に吸着したことで、HMORが$$gamma$$線から吸収したエネルギーが効率よく分解反応に使われたためと考えられる。

論文

Experimental setup and procedure for the measurement of the $$^7$$Be(n,p)$$^7$$Li reaction at n_TOF

Barbagallo, M.*; Andrzejewski, J.*; Mastromarco, M.*; Perkowski, J.*; Damone, L. A.*; Gawlik, A.*; 木村 敦; n_TOF Collaboration*; 他122名*

Nuclear Instruments and Methods in Physics Research A, 887, p.27 - 33, 2018/04

Following the completion of the second neutron beam line and the related experimental area (EAR2) at the n_TOF spallation neutron source at CERN, several experiments were planned and performed. The high instantaneous neutron flux available in EAR2 allows to investigate neutron induced reactions with charged particles in the exit channel even employing targets made out of small amounts of short-lived radioactive isotopes. After the successful measurement of the $$^7$$Be(n,$$alpha$$)cross section, the $$^7$$Be(n,p)$$^7$$Li reaction was studied in order to provide still missing cross section data of relevance for Big Bang Nucleosynthesis (BBN), in an attempt to find a solution to the cosmological Lithium abundance problem. This paper describes the experimental setup employed in such a measurement and its characterization.

論文

Angular distribution of $$gamma$$ rays from neutron-induced compound states of $$^{140}$$La

奥平 琢也*; 高田 秀佐*; 広田 克也*; 木村 敦; 北口 雅暁*; 古賀 淳*; 長元 孝介*; 中尾 太郎*; 岡田 晏珠*; 酒井 健二; et al.

Physical Review C, 97(3), p.034622_1 - 034622_15, 2018/03

The angular distribution of individual $$gamma$$ rays, emitted from a neutron-induced compound-nuclear state via radiative capture reaction of $$^{139}$$La$$(n,gamma)$$ has been studied as a function of incident neutron energy in the epithermal region by using germanium detectors. An asymmetry $$A_{LH}$$ was defined as $$frac{N_{L}-N_{H}}{N_{L}+N_{H}}$$, where $$N_L$$ and $$N_H$$ are integrals of low- and high-energy region of a neutron resonance respectively, and we found that $$A_{LH}$$ has the angular dependence of $$(A cos theta_{gamma} + B)$$, where $$theta_{gamma}$$ is the emitted angle of $$gamma$$ rays, with $$A =- 0.3881 pm 0.0236$$ and $$B =- 0.0747 pm 0.0105$$ in 0.74-eV p-wave resonance. This angular distribution was analyzed within the framework of interference between s- and p-wave amplitudes in the entrance channel to the compound-nuclear state, and it is interpreted as the value of the partial p-wave neutron width corresponding to the total angular momentum of the incident neutron combined with the weak matrix element, in the context of the mechanism of enhanced parity-violating effects. Additionally, we use the result to quantify the possible enhancement of the breaking of time-reversal invariance in the vicinity of the p-wave resonance.

論文

Characterization of germanium detectors for the measurement of the angular distribution of prompt $$gamma$$-rays at the ANNRI in the MLF of the J-PARC

高田 秀佐*; 奥平 琢也*; 後藤 文也*; 広田 克也*; 木村 敦; 北口 雅暁*; 古賀 淳*; 中尾 太郎*; 酒井 健二; 清水 裕彦*; et al.

Journal of Instrumentation (Internet), 13(2), p.P02018_1 - P02018_21, 2018/02

In this study, the germanium detector assembly, installed at the Accurate Neutron Nuclear Reaction measurement Instruments (ANNRI) in the Material and Life Science Facility (MLF) operated by the Japan Proton Accelerator Research Complex (J-PARC), has been characterized for extension to the measurement of the angular distribution of individual $$gamma$$-ray transitions from neutron-induced compound states. We have developed a Monte Carlo simulation code using the GEANT4 toolkit, which can reproduce the pulse-height spectra of $$gamma$$-rays from radioactive sources and (n,$$gamma$$) reactions. The simulation is applicable to the measurement of $$gamma$$-rays in the energy region of 0.5-11.0 MeV.

論文

Radiative neutron capture on $$^{242}$$Pu in the resonance region at the CERN n_TOF-EAR1 facility

Lerendegui-Marco, J.*; Guerrero, C.*; Mendoza, E.*; Quesada, J. M.*; Eberhardt, K.*; Junghans, A. R.*; 木村 敦; n_TOF Collaboration*; 他126名*

Physical Review C, 97(2), p.024605_1 - 024605_21, 2018/02

This paper presents a new time-of-flight capture measurement on $$^{242}$$Pu carried out at n_TOF-EAR1(CERN), focusing on the analysis and statistical properties of the resonance region, below 4 keV. The $$^{242}$$Pu(n,$$gamma$$)reaction on a sample containing 95(4) mg enriched to 99.959% was measured with an array of four C$$_6$$D$$_6$$ detectors and applying the total energy detection technique. The high neutron energy resolution of n_TOF-EAR1 and the good statistics accumulated have allowed us to extend the resonance analysis up to 4 keV, obtaining new individual and average resonance parameters from a capture cross section featuring a systematic uncertainty of 5%, fulfilling the request of the NEA.

論文

Measurement of the neutron capture cross-section of $$^{133}$$Cs as a part of the ImPACT project

Hales, B. P.; 中村 詔司; 木村 敦; 岩本 修

JAEA-Conf 2017-001, p.199 - 203, 2018/01

As part of the ImPACT project, it is currently planned to measure the neutron cross-section of $$^{135}$$Cs (half-life $$2.3 times 10^6$$ y), a long-lived fission product (LLFP), via neutron time-of-flight (TOF) method at the Japan Proton Accelerator Research Complex (J-PARC). Both $$^{133}$$Cs (natural Cs, stable) and $$^{137}$$Cs (half-life $$30.0$$ y) are unavoidable contaminants in the $$^{135}$$Cs sample. In working towards the measurement of $$^{135}$$Cs, a measurement of non-radioactive $$^{133}$$Cs has been conducted. The neutron capture cross-section of $$^{133}$$Cs in the thermal to epithermal energy region was experimentally measured via neutron TOF method at J-PARC. Measured results show good agreement with JENDL in the energy region below 10 eV.

論文

Research on neutron capture cross sections at J-PARC in ImPACT Project

中村 詔司; 木村 敦; Hales, B. P.; 岩本 修; 津幡 靖宏; 松村 達郎; 芝原 雄司*; 上原 章寛*; 藤井 俊行*

JAEA-Conf 2017-001, p.15 - 22, 2018/01

高レベル放射性廃棄物にかかわる環境負荷低減技術の基礎データとして、長寿命放射性核種の中性子核データが求められている。革新的研究開発推進プログラム(ImPACT)が平成26年10月より開始された。その事業の中の「核反応データ取得(Project 2)」で、原子力機構のプロジェクト研究として"J-PARC/MLF/ANNRIにおける中性子捕獲反応断面積測定研究"を開始した。本プロジェクト研究では、高レベル放射性廃棄物に含まれる長寿命核分裂生成核種(LLFP)のうち、$$^{135}$$Cs(半減期230万年)を選定し、中性子捕獲反応断面積を測定する。$$^{135}$$Csを測定する際には、試料中に化学的に分離できない$$^{137}$$Csが不純物として混在する可能性があり、$$^{135}$$Csのデータを精度よく測定するためには、不純物である$$^{137}$$Csの寄与を分ける必要がある。このために、併せて$$^{137}$$Cs等の同位体核種の中性子捕獲断面積データも測定する。また、試料の入手が困難なLLFP核種のうち$$^{79}$$Seについて、試料整備の可能性検討を行う。本発表では、ImPACT事業における本プロジェクト研究の開発計画の概要について、研究の目的、過去の報告データの現状、全体スケジュールと進捗などと併せて、現時点で得られている成果について発表する。

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