The use of pulsed compact neutron systems to implement energy-resolved prompt-gamma activation analysis is herein assessed in detail for the quantitative and non-intrusive detection of chlorine and sulfur in cementitious media, two exogenous contaminants commonly found in buildings, civil infrastructures, or archeological artifacts. To this end, we have examined the current capabilities of the RIKEN RANS-I pulsed source across its neutron energy spectrum using its room-temperature moderator. We achieve up to a threefold improvement relative to previously reported limits of detection via the selective use of the γ -ray yield in the wavelength interval 2-4 Å. Under these conditions, measurement times of a few minutes are sufficient to attain sensitivities in the sub-millimol μ mol

The nano-sized graphene with a petaland seed-like structure may induce neutron coherent scattering. We have studied a possible effect according to which the increase of the number of graphene seed-like structures produces an enhancement of the coherent scattering. To evaluate this, we focused on Raman spectra that characterize the stacking structure, crystal irregularities, and defects promoted by graphene growth. By focusing on this information, we tried to find parameters related to the nano-sized structure of graphene, and explored whether they can be related to the coherent scattering. As a result, it is suggested that the increase of the G/D ratio and the decrease of the G/2D ratio in the Raman spectra correlate strongly with the increase of the coherent scattering.

Herein, we have used so-called Compact Accelerator-driven Neutron Systems (CANS) to explore the properties and performance of composite cement foams for thermal-energy storage. To this end, energy-resolved neutron imaging and tomography were implemented on RIKEN RANS-I, and these data were complemented by thermal conductivity measurements. The ability to pulse this CANS down to tens of microseconds enables data collection across the available neutron energy spectrum for different foam formulations. With relatively modest L/D ratios of ∼35, it is possible to attain a spatial resolution in the millimeter range, and useful images can be collected in as little time as 3 min. Volume reconstruction was performed via angular scans from 0° to 180° in 10° steps, corresponding to a total of 19 images collected over a period of less than an hour. Key to the above has been the deployment of recently developed algorithms and techniques for the analysis of sparse data. On the basis of these results, the existing capabilities of RIKEN RANS-I and similar CANS provide us with new, nonintrusive, and quantitative measures of key performance parameters, including the degree of porosity over relevant length scales typical in these construction materials. In combination with thermal-conductivity data, these results also enable an assessment of insulating performance, with a view to its further optimization.

To enhance the intensity of neutron beams, attention has been focused on the coherent scattering caused by nano-sized particle ensembles, and the use of nano-diamonds has been actively considered. Graphene, which has an sp2 carbon crystal structure, has a larger van der Waals force compared to sp3 carbon crystal structure such as nano-diamonds. Additionally, the bonding force between carbon atoms in graphene is strong, which makes it easier to mold into a large block and plate and to adapt to higher radiation fields. However, graphene is easily to cause aggregation due to its large van der Waals force, making it difficult to form a nano-sized three-dimensional structure. To address this problem, we focused on the hot isostatic pressing (HIP) method, which uses resin powder as the raw material and produces vapor-phase-grown graphene through HIP treatment. We have reported a method for producing free-standing, three-dimensional graphene called "graphene flower" made of nanosized graphene and a method for controlling the nano-size of graphene. Additionally, we presented a prototype of a graphene neutron reflector and measured the coherent scattering of neutrons by graphene for the first time. In this paper, we will report on the optimization of the graphene manufacturing method using the HIP process to improve the coherent scattering performance of neutrons.

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.

It is proposed that nanosized graphene aggregation could facilitate coherent neutron scattering under particle size conditions similar to nanodiamonds to enhance neutron intensity below cold neutrons. Using the RIKEN accelerator-driven compact neutron source and iMATERIA at J-PARC, we performed neutron measurement experiments, total neutron cross-section and small-angle neutron scattering on nanosized graphene aggregation. For the first time, the measured data revealed that nanosized graphene aggregation increased the total neutron cross-sections and small-angle scattering in the cold neutron energy region. This is most likely due to coherent scattering, resulting in higher neutron intensities, similar to nanodiamonds.

NSGA-MC as a multiobjective shielding design method can optimize the shielding parameters aiming at multiple objectives through evolutionary computations by Monte Carlo N-Particle (MCNP) calculations and a genetic algorithm, nondominated sorting genetic algorithm II (NSGA-II). In our previous study, NSGA-MC has been proven to be effective through simulation results by applying to the target shielding design of a compact accelerator-driven neutron source. However, to confirm the effectiveness of NSGA-MC, experimental verifications are critically important. Thus, we planned to experimentally study sets of multilayer shielding structures consisting of PE, B4C, and Pb layers and optimize with NSGA-MC with two objectives of equivalent dose rate and material density. Three cases identified from the Pareto fronts obtained by NSGA-MC and a nonoptimized case based on RANS target station shielding configuration were tested by utilizing RIKEN accelerator-driven compact neutron source (RANS). The dose rates of neutron and gamma ray after neutron beam penetrated the shielding material were measured with commercially available neutron and gamma-ray dosimeters based on these shielding configurations. Discussions were made on experimental results and simulation results. Validation was assured by this experiment within 42%.

The RIKEN Accelerator-driven compact Neutron Source-II (RANS-II) based on the Li-7(p,n)Be-7 reaction with 2.49 MeV proton injection was installed in a small area of the experimental hall, where the scattered radiation is expected to strongly influence experiments. Therefore, we have begun to study the radiation characteristics of the RANS-II hall by simulation with the Particle and Heavy Ion Transport code System (PHITS) and by experiments to clearly identify the scattered component. In addition, to suppress the background, a collimator is studied with respect to its size, shape, and materials. With the use of the phi 30 mm borated polyethylene collimator, we found that the background becomes less than 1% of the extracted neutron beam intensity 1.0 m from the Li target. For the experiment, neutron suppression was characterized by measuring the neutron dose rate with a neutron dosimeter and a collimator. The suppression ability of the neutron beam was confirmed by comparing the results of simulations with those of experiments.

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.

Double-differential cross-sections of the 9 Be(p,xn) reaction are newly evaluated based on the Wakabayashi’s function and neutronics analysis up to 12 MeV for a new nuclear data library, JENDL-5. We devoted our efforts especially to the re-optimization of the absolute cross-sections and the interpolation of the neutron energy spectra. Through the comparisons between the thick target yield measurements and Monte-Carlo simulations at different proton energies and neutron emission angles, we conclude that JENDL-5 gives the best evaluation in the world. Keywords Nuclear data , Be(p,xn) reaction , Double-differential cross-section , Wakabayashi’s function , Interpolation , Neutronics simulation , Thick target yield , JENDL-5

Double-differential cross-sections of the 9Be(p,xn) reaction are newly evaluated based on the Wakabayashi’s function and neutronics analysis up to 12 MeV for a new nuclear data library, JENDL-5. We devoted our efforts especially to the re-optimization of the absolute cross-sections and the interpolation of the neutron energy spectra. Through the comparisons between the thick target yield measurements and Monte-Carlo simulations at different proton energies and neutron emission angles, we conclude that JENDL-5 gives the best evaluation in the world.

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.

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.

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.

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 B4C 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.

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 x10(3)n/cm(2)/mu 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.