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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. [ABSTRACT FROM AUTHOR]

We have optimized a cold neutron moderator to be operated at the RIKEN accelerator-driven compact neutron source (RANS) to broaden cold neutron applications and provide more choices for RANS users. We selected a safe and easy to manage material, mesitylene, as the RANS cold moderator. An efficient moderator system was designed by studying and optimizing a coupled cold neutron moderator of mesitylene at 20 K with a polyethylene (PE) pre-moderator at room temperature in the slab geometry with Particle and Heavy Ion Transport code System (PHITS) simulations. The parameters of mesitylene and PE thickness, the reflector, and the shielding configuration were studied to increase cold neutron intensities within [0.1 meV, 10 meV] and thermal neutron intensities within [10 meV, 100 meV]. Consequently, an integrated cold neutron intensity of 1.15 × 1 0 3 n/cm 2 ∕ μ A at 2 m from the neutron-producing target was finally achieved, which was 12 times higher than that of the current RANS moderator with 4 cm PE according to simulation results. The cold and thermal neutron intensities of the optimized cold neutron moderator was compared with a cold neutron source based on solid methane, which has a beryllium target and the same proton energy as RANS. The results showed attractive application prospect of mesitylene as cold neutron moderator material. [ABSTRACT FROM AUTHOR]