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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]

To characterize the dose rate distribution in an experimental hall of a RIKEN accelerator-driven compact neutron source (RANS) based on the 9Be(p, n) reaction with 7 MeV proton injection, systematical measurements and calculations for neutron and gamma-ray dose rates by GEometry ANd Tracking (GEANT), Particle and Heavy Ion Transport code System (PHITS), and Monte Carlo N-Particle (MCNP) codes were performed. Calculations always underestimated measurements when proton beam loss effect was not considered. Relatively good agreements were observed among the different simulation codes. To explain the underestimations, the additional dominant neutron and gamma-ray sources due to proton beam loss were identified at the position around exit of the drift tube linac (DTL), made of copper, and the beam pipe from quadrupole (Q) magnets to steering (ST) magnets, made of aluminum, from measurements with placing collimators along linac. The beam loss fractions of 2%–3% on copper and 1% on aluminum, respectively, were the most appropriate estimation. In addition, we proposed the possible measures to reduce the measured total dose rate of $3.8~\mu $ Sv/h at the operator position in the control room, with the addition of a wall at the entrance of experimental hall and extension of borated polyethylene (BPE) at the end of the beam. As a result, the dose rate became 2.5 times lower than the current one. [ABSTRACT FROM AUTHOR]

As the Transportable Accelerator-driven Neutron Source (TANS) for the non-destructive testing of outdoor infrastructure requires efficient neutron production with low power, we studied the target structure design based on the 7Li (p, n) 7Be reaction under a 2.5 MeV proton beam injection. For practical applications of TANS, the neutron attenuation in the forward direction should be as low as possible, thus we decided to investigate water-cooling target structures, including an edge-cooling type. Relevant parametric simulations of the material thickness of target structures and water flow rates were carried out in both edge-cooling and conventional back-cooling types. The comparison of neutron attenuation and cooling capability shows that the edge-cooling target has a good performance not only in keeping the temperature within a reasonable range but also in providing the necessary intensity of forward-emitting neutrons with less attenuation, which is suitable for practical applications of TANS. And the stress analysis proves the engineering feasibility of edge-cooling target in operation. In addition, the induced radioactivities and associated dose rates were estimated for the edge-cooling structure model. [ABSTRACT FROM AUTHOR]

Abstract: A cross-flow type (CFT) mercury target with flow guide blades has been developed for JSNS that suppresses the generation of a stagnant flow region near the beam window where the peak power density is generated due to the spallation reaction. In addition, a flat type beam window has been applied to the CFT target that suppresses dynamic stress caused by pressure waves, that have been estimated with an elastic model for mercury. Recent experimental results obtained by using a proton beam incident to mercury targets suggested that using a cut-off pressure model for mercury would be appropriate for predicting a dynamic stress behavior in a target vessel. Dynamic stress analyses were carried out with the cutoff pressure model in which the negative pressure less than −0.15MPa could not be sustained. The dynamic stress generated in the flat beam window became much larger than that in a semi-cylindrical type window as a result of using the cut-off pressure model. Regardless, even the stress generated in the semi-cylindrical type beam window exceeded the allowable stress of SS316L under the peak power density of 668MW/m3. In order to decrease the dynamic stress in the semi-cylindrical beam window, the incident proton beam was defocused to reduce the peak power density down to 218MW/m3. Although the dynamic stress could be suppressed to less than the allowable stress, the high power density generated on the end of the flow guide blades due to defocus of the proton beam caused high thermal stress exceeding the allowable stress. Several shapes of blade ends were studied analytically to decrease the thermal stress, that did not affect the mercury flow distribution. A simple thin-end blade showed low thermal stress below the allowable stress. [Copyright &y& Elsevier]

RIKEN accelerator driven compact neutron source II (RANS-II), a neutron source that is designed to serve as a prototype of a next-generation downsized accelerator-based compact system, has been constructed and has successfully generated neutrons. We aim to demonstrate the system's suitability for various applications, such as the on-site degradation diagnosis of concrete infrastructures, analysis of raw materials, and other uses. Based on the 7Li(p,n)7Be reaction for neutron production, the major components of RANS-II include a newly developed ECR ion source, 2.5 MeV RFQ using copper plated steel as a proton accelerator along with a customized solid-state amplifier, and a thin lithium neutron production target deposited on a copper substrate deployed at the end of proton beamline. A movable collimator shielding assembly is placed to shield the neutron and gamma rays produced and extract the neutron beam for experimental purposes. Using this system, we succeeded in transporting a pulsed proton beam onto the Li target and observed neutron production at the target. RANS-II was successfully installed in a dedicated space in the neutronics engineering facility at the RIKEN Wako campus. A preliminary test was conducted to analyze the neutron source characterization using conventional dosimetry for neutrons. Results confirm the validity of the proposed design parameters of the RANS-II prototype. • This paper describes a newly completed accelerator-based neutron source system. • The significance of developing a compact neutron source was explained. • New developments were made for the accelerator, the ion source, the amplifier, the neutron-producing target, and the shielding. • The results of pulsed neutron generation test are described. [ABSTRACT FROM AUTHOR]