Experimental validation of cold neutron source performance with mesitylene moderator installed at RANS

Abstract

The RANS (RIKEN Accelerator driven Neutron Source), one of compact accelerator neutron sources (CANS), tries to expand its performance by installing a cold neutron which may provide new opportunities in many applications. RANS is a low power CANS with a proton beam of 7 MeV and 100 µA at maximum. A moderator system was constructed based on results of optimization design study with mesitylene. Recently, we have done performance tests aiming at showing characteristics as cold neutron source. Cryogenic mesitylene moderator was installed on a plug with a new target moderator reflector configuration of RANS. Experiment using a gas electron multiplier (GEM) detector was carried out to measure neutron spectra of the cold moderator. This paper describes performance of the cold moderator in terms of 1) Cold neutron gain of optimization design with respect to a polyethylene moderator, 2) Temperature dependency of cold neutron spectrum flux regarding scattering kernel (SK), and 3) comparison between experiment and calculation. A note is given for comparison between calculations with different SKs available. Also, two-dimensional imaging of cold and thermal neutron spectrum flux on the viewed surface is shown with a pinhole slit configuration.

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“…It is also difficult to determine how much useful information can be obtained from a 700 W RANS small power source, such as total cross-section and small-angle scattering measurements, when the source intensity is overwhelmingly disadvantageous compared to MW class high-power sources like those at J-PARC [ 19 ]. As a result, the moderator arrangement system was reviewed and experimentally improved with new ideas, such as selecting a slab-type moderator arrangement and incorporating slit-type collimators to increase available neutrons [ 20 ], as one way of finding out the potential of small sources [ 21 ].…”