Si backscattering spectrometer at the pulsed neutron source of J-PARC

Takahashi, Nobuaki; Shibata, Kaoru  ; Kawakita, Yukinobu*; Sato, Taku*; Tsukushi, Itaru*; Nakagawa, Hiroshi   ; Fujiwara, Satoru; Nakajima, Kenji  ; Arai, Masatoshi

A Si-analyzer backscattering spectrometer DNA is proposed to be constructed in the Materials and Life Science Facility of Japan Proton Accelerator Research Complex, in order to research on the dynamics of bio-molecules and proteins. Si(111) and Si(311) analyzers will be mounted in a vacuum vessel located at 43 m away from a coupled moderator to enjoy the highest peak intensity among moderators at the target station. On the other hand, there is a demerit that the pulse-shape of the coupled moderator is broad and has a long tail. Then, the instrument is designed to utilize a pulse-shaping device, which is installed at the beamline as far away from the sample position as possible (at 7.8 m from the source) to sharpen the pulse-shape. By optimizing the pulse-shaping device, we can realize 1 micro-eV energy resolution with 35 micro-eV energy band. This is almost comparable to BSSs at reactor sources. Additionally we can obtain valuable energy resolution by tuning the pulse-shaping device. A novel efficient measurement technique, so-called Repetition Rate Multiplication (RRM) is also planned, i.e., measuring inelastic part is efficiently achievable by using a multi-slit pulse-shaping chopper. In this presentation we will show conceptual design of the instrument. The expected performance will be compared with BSSs at reactor sources as well as BSSs at spallation neutron sources.