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Report No.
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Neutron filtering system for fast neutron cross-section measurement at the ANNRI beamline of MLF/J-PARC

Rovira Leveroni, G.  ; Iwamoto, Osamu ; Kimura, Atsushi  ; Nakamura, Shoji ; Iwamoto, Nobuyuki ; Endo, Shunsuke  ; Katabuchi, Tatsuya*; Terada, Kazushi*; Kodama, Yu*; Nakano, Hideto*; Hori, Junichi*; Shibahara, Yuji*

In order to circumvent the current double-bunch predicament in the keV region, a neutron filtering system involving the use of filter material with the intrinsic characteristic of a sharp minima in the neutron total cross section was implemented at the ANNRI beamline. Quasi-monochromatic neutron beam can be created using such materials with the appropriate thickness as only the neutrons with the energy of the sharp minima can be transmitted through. $$^{nat}$$Fe, $$^{nat}$$Si, $$^{nat}$$Cr are seen as suitable candidates to tailor quasi-monoenergetic neutron peaks with averaged energies of 23.5 keV (Fe); 54 and 144 keV (Si); and 46 and 136 keV (Cr). In this presentation, the main features of the neutron filtering system together with performance evaluations will be presented. The time distribution of the incident filtered neutron flux at ANNRI was measured in both capture experiments with a NaI(Tl) spectrometer and transmission experiments involving the use of Li-glass detectors. In addition, the energy distribution within the filtered peaks was determined from Monte-Carlo simulations with the PHITS code. Finally, the first cross section results using the neutron filtering system will be shown and discussed in order to assess the performance in neutron capture cross section measurements.

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