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Report No.
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Measurements of spatial distribution of intensity and energy spectrum of neutrons from coupled hydrogen moderators by using a position sensitive detector (Cooperative research)

Kai, Tetsuya ; Kamiyama, Takashi*; Hiraga, Fujio*; Kato, Takashi; Kiyanagi, Yoshiaki*

Spatial distributions of neutron intensities were measured based on the pinhole camera principle to confirm a peculiar one for a para-hydrogen (H$$_2$$) moderator by neutron transportation calculations. Para- H$$_2$$ and ortho-rich-H$$_2$$ (ortho/para ratio was 60:40-70:30) were utilized. The results are consistent with the calculations. Position dependences of energy spectra were measured for further discussions. Both moderators exhibit the intensity enhancements at the fringe part between 15 and 100 meV. Below 15 meV, the para-H$$_2$$ moderator exhibits higher intensity at the fringe part, while a intensity decrease was recognized at the fringe part of the ortho-rich-H$$_2$$ one. The reasons for the peculiar distribution are due to the characteristics of para- H$$_2$$: the effective slowing-down reaction for thermal neutrons and the higher transmission rate for cold neutrons. The present result is one of the basis confirming the reliability of design calculation used in the J-PARC project.

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