Systematic effects on cross section data derived from reaction rates in reactor spectra and a re-analysis of Am reactor activation measurements

原子炉中性子スペクトル照射により導出される断面積データの系統的誤差とAmの中性子放射化断面積データの再解析

erovnik, G.*; Schillebeeckx, P.*; Becker, B.*; Fiorito, L.*; 原田 秀郎   ; Kopecky, S.*; Radulovic, V.*; 佐野 忠史*

erovnik, G.*; Schillebeeckx, P.*; Becker, B.*; Fiorito, L.*; Harada, Hideo; Kopecky, S.*; Radulovic, V.*; Sano, Tadafumi*

原子炉中性子スペクトルで照射することにより得られる積分データから中性子断面積を導出する手法に関して、Westcottの記法を用いる断面積導出法の有効性について検討を行った。この結果、本手法で得られる精度は、中性子束エネルギー分布の精度に大きく依存すること、特に、導出される共鳴積分値が大きな影響を受けることを定量的に示した。また、中性子断面積のエネルギー依存性が既知の場合は、その情報を用いてこの影響を補正する手法を提案した。本手法を適用して、Amの熱中性子捕獲断面積を再解析した結果、720(14)bを得た。

Methodologies to derive cross section data from spectrum integrated reaction rates were studied. The Westcott convention and some of its approximations were considered. The accuracy of the results strongly depends on the assumptions that are made about the neutron energy distribution, which is mostly parameterised as a sum of a thermal and an epi-thermal component. Resonance integrals derived from such data can be strongly biased. When the energy dependence of the cross section is known and information about the neutron energy distribution is available, a method to correct for a bias on the cross section at thermal energy is proposed. Reactor activation measurements to determine the thermal Am(n, ) cross section reported in the literature were reviewed, where the results were corrected to account for possible biases. These data combined with results of time-of-flight measurements give a capture cross section 720 (14) b for Am(n, ) at thermal energy.