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We have been developing nanosized graphene, called graphene flower, as a material that induces coherent scattering very cold neutrons. Previous experiments have found that the seed part of the graphene flower is more effective than the petal part in increasing the coherent scattering. Based on these results, we found that further modification of the graphene flower to increase the seed portion increased the total cross-section, although it did not reach the level of nanodiamonds. [ABSTRACT FROM AUTHOR]

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 started the development of a transportable neutron salt-meter, we call it RANS-μ, combining a 252Cf neutron source and a prompt gamma neutron activation analysis. Trials of chloride detection measurement with RANS-μ were performed outdoor using removed bridges damaged by chloride attack at an outdoor yard in Public Works Research Institute (PWRI) and a test bridge in Fukushima Robot Test Field. For the measurement at PWRI, the results obtained by RANS-μ were compared with those of the automatic potentiometric titration by drilled powder, and then consistent results were obtained. [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]

We studied the feasibility of a portable salt-meter incorporating a prompt gamma neutron activation analysis with a californium-252 neutron source to meet urgent demands for non-destructive methods without pre-processing in large bulk materials such as concrete structures. This technique is aiming at the chloride ion concentration in concrete structures with a depth profile from the surface to steel bar. From the portability point of view, a californium-252 neutron source is adopted and we have performed a preliminary experiment and simulations with a simple geometry. In this paper, we describe the performances of salt detection sensitivities by applying the prompt gamma neutron activation analysis. [ABSTRACT FROM AUTHOR]

To find the optimal shielding design for compact accelerator-driven neutron sources (CANS) using multiobjective optimization, we developed a new method called nondominated sorting genetic algorithm-Monte Carlo method (NSGA-MC). NSGA-MC employs NSGA-II to optimize the shielding parameters based on calculations made by the Monte Carlo N-Particle Transport Code (MCNP). A layered shielding configuration with two materials of borated polyethylene (BPE) and lead (Pb) in the order of BPE/Pb/BPE/Pb for RIKEN Accelerator-driven Compact Neutron Source (RANS) was examined using this method, and two objectives were optimized simultaneously: equivalent dose rate and shielding structure weight. As a result, a tradeoff relationship between the objectives was finally obtained in the form of a Pareto front. The optimization results revealed significant improvements compared with the current RANS shielding configurations in terms of both dose and weight. The results indicate that a reduction in shielding weight of about 60% can be obtained by adopting the optimized shielding structure design, without sacrificing shielding performance. The performance of the method was discussed by showing advantages of NSGA-MC over the so-called weight sum method. [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: Construction of a 1MW pulse spallation neutron source (JSNS) is in progress under the J-PARC project to provide a vital experimental environment for breakthroughs in neutrons researches with emphasis in materials and life sciences. An overview of the JSNS is given in terms of 1MW power regime, the mercury spallation target, cryogenic H2 moderators, and the central station with 23 independent neutron beam shutters. Conventional facility construction and neutron instrumentation scheme are briefly shown along with the technical research and development with emphasis on material issues. [Copyright &y& Elsevier]

Our primary goal and mission is to construct a 1-MW pulse neutron source and a muon source as a materials and life science experimental facility. We sincerely expect a wide variety of new research, applications, and technologies from this environment. MLF is also expected to play a key role as an incubation ground for more synthetic synergy of science, appreciating the high performance of the source capability. MLF or J-PARC is a great step for this purpose. [ABSTRACT FROM AUTHOR]

Chloride attack is a serious problem that decreases the durability of concrete structures of bridges and highways. A compact neutron salt meter with a252Cf neutron source and germanium (Ge) gamma-ray detector based on prompt gamma-ray neutron activation analysis (PGNAA) has been proposed to determine the chlorine concentration in concrete structures. The Optimization of the dimensions of its components, such as polyethylene (PE) moderator, graphite reflector, and lead shield, as well as the positions of the 252Cf source and the Ge detector has been performed to make it highly sensitive for the detection of gamma-rays of chlorine, in addition to lightweight and small volume for in situ use. The results demonstrated that gain factors of 2.5 and 2.2 were obtained for gamma-ray intensity of chlorine and chlorine-to-hydrogen ratio (CHR), respectively, whereas the weight and volume became 19.1% and 23.4%, respectively, compared with the reference setup. The effectiveness of optimization was confirmed by preliminary experiments. • A portable device to measure chlorine concentration in concrete based on PGNAA with 252Cf neutron source was proposed. • Optimization was performed by Geant4 code to make it highly sensitive and lightweight. • 10 times gain with respect to detection sensitivity per weight was achieved through the optimization. • Effectiveness of the optimization was validated by experiments. [ABSTRACT FROM AUTHOR]

Abstract: A systematics of (n,2n) partial excitation functions was studied on the basis of our 58 sets of experimental data measured using intense neutron source facilities of FNS at the Japan Atomic Energy Agency and of OKTAVIAN at Osaka University. The empirically predictive formulas based on the evaporation theory are applicable for the neutron energy between 13.4 and 14.9MeV, and in the mass range between 14 and 238. About 83% of the cross sections and the slopes of excitation functions can be reproduced within an uncertainty of 15%. The formulas were expressed in terms of a mass number A, an asymmetry parameter S =(N − Z)/A, and threshold energies of the (n,2n) and (n,3n) reactions, where N and Z are the neutron and proton numbers for the target nuclei, respectively. The excitation functions were well reproduced for the nuclei in the region with S <0.05 and 14⩽ A ⩽58 for the first time. The general characteristics of the excitation functions, consisting of steep rising in the light mass nuclei, gently-sloping or nearly flat in the middle and heavy mass nuclei, and slow falling in the heavy mass regions with possible (n,3n) reactions, are well expressed. [ABSTRACT FROM AUTHOR]

Abstract: Neutronic performance of a poisoned hydrogen moderator was studied in details. Using a simple rectangular-shape moderator-model, its basic characteristics were studied as a function of the poison position. We, for the first time, turned up that the pulse width was rather decreasing with increasing the moderator thickness of the back part from the poison. This is due to the fact that source neutron pulses entering into a front part of the poison through the back part exhibit a fast rise shape while those from the target and the reflector through the decoupler and liner exhibit a broad shape. Next, we studied the pulse deterioration in regard to a finite beam-extraction-angle by using a more realistic moderator shape, canteen shape and a concave-shape. It turns out that the pulse deterioration is considerably large in both cases even at a small extraction angle. The concave-shape moderator indicates a finite improvement compared to the canteen-shape one. Finally, merits and demerits of two poison materials, Cadmium and Gadolinium, were discussed taking into account the burn-up issue of poison with the operation time. [Copyright &y& Elsevier]

Neutronic performance of a coupled hydrogen moderator was studied as a function of para hydrogen concentration, moderator thickness and height, premoderator thickness, etc. for the J-PARC spallation neutron source. It was found that a thick (140 mm) moderator with 100% para-hydrogen was optimal to provide a high time- and energy-integrated neutron intensity below 15 meV and high pulse-peak intensities at lower energies. Distribution of the cold neutrons on a moderator viewed surface was studied and found to exhibit an intensity-enhanced region at the fringe part near the premoderator. This rather peculiar distribution suggested that the moderator and the viewed surface must be designed so as to take the full advantage of the brighter region near the premoderator. [Copyright &y& Elsevier]

This study explores high-energy neutron components of the extracted neutron beam at J-PARC pulsed neutron source using the foil activation method with threshold reactions. Foils of aluminum, gold, bismuth, niobium, and thulium were used to cover the neutron energy range from 0.3 MeV to 79.4 MeV. The experiment was performed using neutron beams of BL10 (NOBORU). The foils were irradiated by a neutron beam at 13.4 m from the moderator. To characterize high-energy neutron fields for irradiation applications, reaction rates in three different configurations with and without B 4 C slit and Pb filter were examined. To compare the experiments with calculations given for the user, reaction rates for corresponding reactions were calculated by the PHITS code with the JENDL-3.2 cross sections and the JENDL dosimetry file. Although there was a systematic tendency in C/E (Calculation/Experiment) ratios for different threshold energies, which C/E ratio decreased as threshold energy increased up to 100 MeV, all C/E ratios were in the range of 1.0 ± 0.2. This indicated that high-energy neutron calculations were adequate for the analysis of experimental data for NOBORU users. [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]

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]

Abstract: Supercritical hydrogen is selected as a moderator material in Japan Spallation Neutron Source Facility (JSNS). Total nuclear heating in the moderator is estimated to be 3.75kW at 1MW proton beam power, which provides a hydrogen cryogenic system as a heat load. The heat load changes significantly due to pulse proton beam operation. A control system to mitigate such heat load changes is required for the hydrogen cryogenic system in order to maintain stable operation and steady cold neutron generation. A hybrid control system, which consists of a heater and an accumulator, is developed and installed in the system. In order to build the optimal control method, the behaviors of hydrogen loop are analyzed with an original computer code. The analysis suggests that a stability of hydrogen system and a cold neutron beam performance by the hybrid fluctuation control system are compatible. [Copyright &y& Elsevier]

Abstract: Neutron beam shutter system of Japan Spallation Neutron Source (JSNS) in the J-PARC has been designed under a particular precondition that every shutter should be controlled and maintained independently. This is very important from the viewpoints of usability and flexibility of a beam-line. To satisfy this precondition, a compact ball screw jack system sustaining a shutter gate by two shafts with rigid flanges was designed. Every shutter gate contains an insert as a beam-line component. An allowance of misalignment for the insert was evaluated by Monte Carlo simulations, and 1mrad which corresponds to maximum beam loss at 2% was set as a target value. Alignment for an insert within 1mrad in a vertical plane was achieved by an ex-situ adjustment at installation work. For the alignment in a horizontal plane, on the other hand, an in-situ adjustment mechanism was developed to meet the target value. [Copyright &y& Elsevier]