Background issues on AMATERAS

AMATERASにおけるバックグラウンド

菊地 龍弥  ; 中島 健次  ; 河村 聖子   ; 川北 至信  ; 稲村 泰弘  ; 沢辺 正樹; 若井 大介*

Kikuchi, Tatsuya; Nakajima, Kenji; Kawamura, Seiko; Kawakita, Yukinobu; Inamura, Yasuhiro; Sawabe, Masaki; Wakai, Daisuke*

We are operating a cold-neutron disk-chopper spectrometer AMATERAS installed at MLF, J-PARC and carrying out many experiments so far. The reduction of background is one of the important issues in operating the spectrometers. At AMATERAS, we have already spent anomalous effort to reduce the background. As a result the current level of background of AMATERAS is 13 counts per an hour and a meter of a PSD-detector, and we are still continuing our work to realize further reduction of the background. Now we focused on several issues. For example, the -ray background is caused by the prompt -ray that occurred by the sample itself and the cadmium metal for background reduction. On AMAERAS He detectors which are low sensitivity of -ray are used, but nonetheless the -ray becomes an obstacle of the measurements. The time-independent background is thought that it is caused by the environmental neutrons. This background is time independent. It is constant regardless of the operation of the proton accelerator and ON/OFF of the neutron beam.