Improvement of measurement of neutron spectral intensity at JSNS/J-PARC

JSNS/J-PARCにおける中性子強度測定の改良

原田 正英   ; 及川 健一   ; 甲斐 哲也   ; 明午 伸一郎   ; 高田 弘   

Harada, Masahide; Oikawa, Kenichi; Kai, Tetsuya; Meigo, Shinichiro; Takada, Hiroshi

J-PARCの核破砕中性子源の中性子パルス性能を確認するために、中性子強度と中性子パルス形状を測定した。しかし、He-3検出器システムと金箔放射化法とで測定される中性子強度に相違があった(約20%)。そこで、次の3つの改善を行った。(1)長波長中性子を用いて、He-3中性子検出器の検出効率を測定した。(2)ランダムパルス発生装置を用いて、不感時間補正を行った。(3)同じコリメータ設定条件を用いた。JSNSの実験装置「NOBORU」(BL10)で再測定を行った結果、He-3検出器システムと金箔放射化法とで測定される中性子強度に良い一致を得ることができた(10%以下)。これに加えて、陽子ビーム強度、位置、プロファイル依存性も測定した。その結果を、粒子輸送計算コードPHITSで計算によって分析し、中性子強度が陽子ビームの強度、位置、プロファイルに依存することがわかった。

To confirm neutronic performance of JSNS, we have performed to measure a neutron intensity and a neutron pulse. However, there were a bit discrepancy (20%) between neutron intensities measured by a He-3 neutron detector system and an Au foil activation method. To reduce the discrepancy, we have done the re-measurement with three improvements. (1) The detection efficiency of the He-3 neutron detector was precisely determined by long wave neutrons. (2) Dead time was corrected using a random pulser. (3) The same collimation setting was adopted. As a result of the measurement at a neutron instrument "NOBORU" (BL10) of JSNS, we obtained good agreement (below 10%) between data measured by the He-3 neutron detector system and the Au foil activation method. Especially, the same collimation setting was important to reduce the discrepancy due to a spatial distribution of the neutron beam. In addition, neutron intensities with changing a proton beam intensity, profile and position were measured by the He-3 neutron detector system. And we also analyzed by the calculation with PHITS. As a result, it was found that neutron intensity depends on the proton beam condition. We also found good agreement between the measurement and the PHITS calculation.