Measurement of intensity and spatial distribution of thermal neutrons with the large-area gold-foil activation method at the Materials and Life science Facility in J-PARC

Harada, Masahide; Yamaguchi, Yuji; Kawamura, Seiko; Kofu, Maiko; Nirei, Masami; Haga, Katsuhiro; Oku, Takayuki; Matsuura, Masato*; Kusaka, Katsuhiro*; Nakayama, Haruki*

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In the Materials and Life science experimental Facility (MLF) at J-PARC, 3 GeV proton beam is injected into a mercury target to provide neutrons produced by spallation reactions to neutron instruments, and as of June 2023, MLF is operating at 800 kW proton beam output. The intensity of neutrons provided to the neutron instruments is an important factor to characterize the performance of the neutron instruments. So far, neutron intensity measurements have been done with He-3 counters and gold foil activation methods. To measure both spatial distribution and absolute value simultaneously with high accuracy was an issue. To solve this issue, we proposed the large-area gold-foil activation method for thermal neutrons. In this presentation, we will explain the method of the large-area gold foil activation method and report examples of its application to neutron intensity and distribution measurements at BL02, BL03, and BL14.