Shape Of Neutron Spectrum Research Articles

Development and validation of a Bayesian unfolding program using OpenBUGS open-source software for Bonner spheres neutron spectrometry

This study presents the development of a novel unfolding program based on a Bayesian method for Bonner spheres spectrometry. The program incorporates a priori information on the neutron spectrum, employing a linear superposition of three non-negative parametric functions: thermal-Maxwellian distribution, an intermediate region represented by a straight line in lethargy space (1/E behavior), and the Watt fission distribution for the fast region. The effectiveness of the developed program was validated through its application to two reference cases from the EURADOS 2018 exercise (LINAC and Skyshine), followed by its implementation in characterizing the neutron field around an OB26 neutron irradiator at the Secondary Standards Dosimetry Laboratory (SSDL) of the Nuclear Research Center of Algiers (CRNA), Algeria. While validation results for the LINAC case were promising, achieving comparable neutron spectrum shape and integral quantities to the reference, challenges were encountered with the Skyshine case. However, these challenges were partially addressed through sensitivity analysis, resulting in slightly improved outcomes compared to the previous participation and to the reference. Application of the program to characterize the neutron field around the OB26 irradiator yielded satisfactory results when compared to reference data. A two-step sensitivity analysis further enhanced the outcomes, initially substituting the Watt fission distribution with the evaporation distribution, thereby improving spectrum shape and integral quantities. Subsequently, utilizing the obtained neutron spectra as prior information for unfolding codes MAXED and GRAVEL ensured stability and agreement with reference data and preliminary results.

Benchmarking of Proton- and Neutron-Induced Nuclear Data with MCNP6.2 Using SINBAD Experiments

The effects of both proton and neutron nuclear data libraries on the neutron field produced in light targets and transported through shielding material were assessed. The general-purpose nuclear data libraries JENDL-4.0/HE, TENDL-2017, ENDF/B-VII.0, ENDF/B-VII.1, ENDF/B-VIII.0, JEFF-3.1.2, and JEFF-3.3 were benchmarked using the MCNP6.2 Monte Carlo transport code. Three experiments from the SINBAD database, namely, 52-MeV protons hitting a carbon target and 43- and 68-MeV protons hitting a 7Li target, were selected for benchmarking. This selection was made according to their relevance for the MYRRHA accelerator-driven system to support the design of beam dumps and shielding of the 100-MeV section of the MYRRHA accelerator. It is demonstrated that the prevailing factor determining the transmitted neutron spectrum shape is the proton library from which the secondary neutrons are sampled. The choice of neutron library applied for the secondary neutron transport in the carbon and lithium targets, concrete and iron shielding, is of second-order significance.

Characterisation of neutron field in large graphite insertion in special core of the LR-0 reactor

Graphite is important reactor material used as a neutron moderator in various reactor designs. It is not only structural material used in previous reactors design but even material to which attention is focused due to the very high-temperature reactor design, which uses graphite as moderator and reflector. Due to the well-characterised cross-section of graphite, it is also a good candidate for neutron shaping experiments. In this kind of experiment, the neutron spectra are modified to the unconventional shape of neutron spectra which can be used to validate cross-section. This paper deals with validation of neutron field in graphite block surrounded by driver core arranged in large special core in LR-0 reactor. The experimentally determined shape of neutron spectra and spatial distribution of neutron flux is compared with the calculation. It is worth noting that the agreement for flux distribution is satisfactory in regions below the moderator level.

Genetic algorithm-based optimization of a target for the production of atmospheric-like neutrons via 100 MeV proton beam

This paper presents the optimization of a white neutron target for 100 MeV proton beam to produce a fast neutron spectrum shape similar to that of the atmospheric neutron at ground level. The neutron target consists of 0.5 mm-thick discs consecutively placed in front of a cooling water channel. A sensitivity analysis is performed with different materials to assimilate resulting neutron spectrum with the ground-level cosmic ray-induced neutron spectrum by applying the genetic algorithm (GA). Optimization of the spectrum is conducted in consideration of neutron impact to semiconductor devices. To reconstruct a target-generated neutron spectrum, parametrization on neutron generation and stopping power by target material and position is configured. The loss function in the GA is defined to evaluate similarity between the target neutron spectrum and the atmospheric neutron spectrum. The GA is modeled with a package of consecutive discs as a gene for optimization, and the length and material of target for each disc are decided throughout generations. As a result, the target is configured with six different materials, with approximately half of the weighted deviation of atmospheric neutrons being compared with any other single-solid neutron target. The GA-based optimization process shown here suggests further use for designing targets with other incident proton energies or neutron spectra for various applications.

Benchmark experiment for bismuth by slab samples with D-T neutron source

A benchmark experiment is carried out with slab sample to validate nuclear data of bismuth by measurement of leakage neutron spectra from 0.8–16 MeV. The measured experiments are performed at China Institute of Atomic Energy with the integral benchmark facility established on the D–T neutron generator. The neutrons leaking from the sample are recorded at the measuring angle of 60° and 120° by time-of-flight technique. To make understanding of the impact of accuracy of data files in evaluated library on the neutron transport simulation, the calculation is carried out by MCNP-4C code with a series of latest available evaluated libraries. The calculated spectra are analyzed by comparing with experimental ones in neutron spectrum shape and C/E values. The result indicates that the theoretical simulation with different data libraries overestimated or underestimated the measured ones in some energy ranges, and the secondary neutron energy distribution and angular distribution in data files have been present to explain it.

Neutron Field Shaping Using Graphite for Reaction Rate Measurements

Abstract Neutron field shaping is the suitable method for validation of cross section in various energy regions. By increasing the share of neutrons of a certain energy interval and decreasing the share of other, a reaction becomes more sensitive to selected neutrons. As a result, reaction cross section can be validated in selected energy regions more precisely. The shaping can be carried out by both neutron filters which are materials with high absorption in some energy region, or by diffusion material changing the shape of neutron spectra by means of slowing down process. In the presented experiments, the neutron field of the light reactor 0 (LR-0) research reactor was shaped by both using graphite blocks inserted into the core and Cd cladding for increasing the epithermal reaction rate share in total reaction rates. The calculations were carried out with the Monte Carlo N-Particle Transport Code 6 (MCNP6) code and the most recent nuclear data libraries. The results in the pure graphite neutron field are in good agreement; in case of Cd cladding, significant discrepancies were reported. In case of the 23Na(n,γ)24Na reaction, overestimation by about 14% was reached in International Reactor Dosimetry and Fusion File (IRDFF-II), results in other libraries are comparable. In case of 58Fe(n,γ)59Fe, the overestimation as high as 18% is reported in IRDFF-II. For 64Zn(n,γ)65Zn reasonable agreement was reached in evaluated nuclear data file (ENDF/B-VIII), where discrepancies in pure graphite neutron field or in case of Cd cladding are about 10–15%.

Determination of k0 and Q0 for 74Se, 113In, 186W and 191Ir targets applying covariance analysis

In the present work, the determinations of k0 and Q0 for 74Se, 113In, 186W and 191Ir targets were performed. The irradiations were conducted near the core of the IEA-R1 4.5 MW swimming-pool nuclear research reactor of the Instituto de Pesquisas Energéticas e Nucleares (IPEN-CNEN/SP – Nuclear and Energy Research Institute), in São Paulo, Brazil. The irradiation position was chosen where the neutron spectrum shape parameter α is very close to zero. For this reason, the correction to be applied for the determination of Q0 is very close to one, thus improving the accuracy of the results. For each experiment, two irradiations were carried out in sequence: the first one with bare samples and the second with a cadmium cover around the samples. All partial uncertainties were considered, applying the covariance matrix methodology. The final results were compared with the literature.

Determination of effective resonance energies for the185Re(n,)186Re and187Re(n,)188Re reactions by cadmium ratio method

The effective resonance energy ($\bar{E}_{r})$ values for the $^{185}$Re(n,$\gamma )^{186}$Re and $^{187}$Re(n,$\gamma )^{188}$Re reactions were measured by using the cadmium ratio method. $^{197}$Au and $^{98}$Mo isotopes were selected as dual monitors to determine the epithermal neutron spectrum shape factor in the irradiation sites of a 37 GBq $^{241}$Am-Be neutron source. The analytical grade rhenium(VII) oxide samples were diluted with Al$_{2}$O$_{3}$ powder to reduce neutron self-shielding effects, and they were put into 1-mm thick small cylindrical polytetrafluoroethylene (PTFE) boxes. Samples were irradiated in a $^{241}$Am-Be neutron source. The activation produced in the irradiated samples was measured in close-counting geometry on the end cap of a Ge detector in order to obtain better counting statistics. The correction factors for gamma-ray self-absorption ($F_{s})$, thermal neutron self-shielding ($G_{th})$, and epithermal neutron self-shielding ($G_{epi})$ effects were determined with suitable approaches. Consequently, the experimental $\bar{E}_{r}$-values were measured to be 3.49 ± 0.54 eV for $^{185}$Re and 41.77 ± 6.79 eV for $^{187}$Re target nuclide, respectively. Furthermore, the $\bar{E}_{r}$-values were theoretically computed through up-to-date resonance data obtained from the ENDF/B VII library using two different approaches. Since there is no experimental data available in the literature for the $\bar{E}_{r}$-values of these isotopes, the results were compared with the theoretical values in the literature.

Characterization of mixed N/G beam of the VR-1 reactor

VR-1 is light water zero-power reactor using IRT-4 M fuel with nominal enrichment of 19.7 wt%, equipped with the radial channel being directly attached to the fuel. Enrichment at the top level of the low enriched uranium limit guarantees that the larger part of non-scattered neutrons in the spectrum is coming from 235U than in case of experimental reactors using enrichments between 2 and 5 wt% (e.g., LR-0). Thus, the measurement of the VR-1 leakage spectrum can be a valuable contribution to the validation process of predicted 235U prompt fission neutron spectrum. Presented second set of measurements is confirming the beam stability at VR-1 and compares the agreement rate in neutron spectrum shape with two benchmarks; light- and heavy water filtered neutron spectrum obtained from spheres. Additionally, gamma spectrum was measured and compared with spherical iron benchmark and VVER-1000 core simulator. Presented measurements have the character of comprehensive characterization of beamline experiments developed at reactor cores with IRT-4 M fuel. Reported good agreement between the experiment and calculation confirm the methodology of using VR-1 as a Mock-Up experiment for benchmarking of high power reactors with IRTM fuel in the neutron transport experiments.

Thermal neutron capture cross-section and resonance integral measurements of 139La(n, $ \gamma$ γ )140La and 140Ce(n, $ \gamma$ γ )141Ce using a Am-Be neutron source

Thermal neutron capture cross-sections and resonance integrals of 139La(n,\( \gamma\))140La and 140Ce (n,\( \gamma\))141Ce are measured with respect to reference reactions 197Au(n,\( \gamma\))198Au and 55Mn(n,\( \gamma\))56Mn using the neutron activation technique. Measurements are carried out using neutrons from an Am-Be source located inside a concrete bunker. Two different methods are used for determining self-shielding factors of activation foils as well as for finding the epithermal neutron spectrum shape factor. For 139 La with reference to 197 Au and 55 Mn the measured thermal cross sections are \( 9.24 \pm 0.25\) b and \( 9.28 \pm 0.37\) b, respectively, while the measured resonance integrals are \( 12.18 \pm 0.67\) b and \( 11.81 \pm 0.94\) b, respectively. For 140 Ce with reference to 197 Au and 55 Mn the measured thermal cross sections are \( 0.44 \pm 0.01\) b and \( 0.44 \pm 0.02\) b, respectively, while the measured resonance integrals are \( 0.55 \pm 0.03\) b and \( 0.54 \pm 0.04\) b, respectively. The present measurements are compared with earlier measurements and evaluations. Presently estimated values confirm the established 139La(n,\( \gamma\))140La cross-sections. The presently measured thermal capture cross-section 140Ce(n,\( \gamma\))141Ce , though lower than the evaluated data, is having higher accuracy compared to previous measurements with large uncertainties. The resonance integral measured is higher (like most previous measurements) than most evaluations requiring a revision of the evaluated data.

Thermal neutron capture and resonance integral cross sections of 45Sc

The thermal neutron cross section (σ0) and resonance integral (I0) of the 45Sc(n,γ)46Sc reaction have been measured relative to that of the 197Au(n,γ)198Au reaction by means of the activation method. High-purity natural scandium and gold foils without and with a cadmium cover of 0.5mm thickness were irradiated with moderated pulsed neutrons produced from the Pohang Neutron Facility (PNF). The induced activities in the activated foils were measured with a high purity germanium (HPGe) detector. In order to improve the accuracy of the experimental results the counting losses caused by the thermal (Gth) and resonance (Gepi) neutron self-shielding, the γ-ray attenuation (Fg) and the true γ-ray coincidence summing effects were made. In addition, the effect of non-ideal epithermal spectrum was also taken into account by determining the neutron spectrum shape factor (α). The thermal neutron cross-section and resonance integral of the 45Sc(n,γ)46Sc reaction have been determined relative to the reference values of the 197Au(n,γ)198Au reaction, with σo,Au=98.65±0.09barn and Io,Au=1550±28barn. The present thermal neutron cross section has been determined to be σo,Sc=27.5±0.8barn. According to the definition of cadmium cut-off energy at 0.55eV, the present resonance integral cross section has been determined to be Io,Sc=12.4±0.7barn. The present results are compared with literature values and discussed.

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral for the \(^{45}\)Sc\((n,\gamma)^{46}\)Sc Reaction with Pulsed Neutrons

Thermal neutron capture cross section and resonance integral for the $^{45}$Sc(n,$\gamma )^{46}$Sc reaction were measured by the activation method using the $^{197}$Au(n,$\gamma )^{198}$Au reaction as a single comparator. The high-purity scandium and gold samples with and without Cd cover with the thickness of 0.5 mm were irradiated in a pulsed neutron field of the 100 MeV electron linac of the Pohang Accelerator Laboratory (PAL). The induced activities in the activated foils were measured with a well calibrated HPGe detector. In order to improve the accuracy of the experimental results the effect of the non-ideal epithermal spectrum was taken in to account by determining the neutron spectrum shape factor ($\alpha )$, and the corrections for the thermal (G$_{th})$ and the resonance (G$_{epi})$ neutron self-shielding effects, the $\gamma $-ray attenuation (F$_{g})$ and the $\gamma $-ray coincidence summing effect were made. The thermal neutron cross-section for the $^{45}$Sc(n,$\gamma )^{46}$Sc reaction has been determined to be $\sigma _{o}$ = 27.6 $\pm $ 0.8 barn. By assuming the cadmium cut-off energy of 0.55 eV, the resonance integral for the $^{45}$Sc(n,$\gamma )^{46}$Sc reaction has been determined to be I$_{o}$ = 12.7 $\pm $ 0.7 bar. The present results are compared with the reference data and discussed.

Thermal neutron capture cross section and resonance integral of the 139La(n,γ)140La reaction

The thermal neutron capture cross section (σ0) and resonance integral cross section (I0) of the 139La(n,γ)140La reaction have been measured relative to that of the 197Au(n,γ)198Au reaction by means of the activation method. High-purity natural lanthanum and gold foils were exposed to pulsed neutrons at the Pohang neutron facility. One set of foils was irradiated directly and a second set of foils was shielded with a cadmium cover of 0.5mm thickness. The induced activities in the activated foils were measured by a γ-ray spectrometer based on a calibrated high purity germanium (HPGe) detector. In order to improve the accuracy of the experimental results the epithermal neutron spectrum shape factor (α) was determined, and the corrections for the thermal neutron self-shielding (Gth), the resonance neutron self-shielding (Gepi), the γ-ray attenuation (Fg) and the γ-ray coincidence summing effects were made. The thermal neutron cross-section for the 139La(n,γ)140La reaction has been determined to be 9.16±0.36 barn, relative to the reference value of 98.65±0.09 barn for the 197Au(n,γ)198Au reaction. By assuming the cadmium cut-off energy of 0.55eV, the resonance integral cross section for the 139La(n,γ)140La reaction is 11.64±0.69 barn, which is determined relative to the reference value of 1550±28 barn for the 197Au(n,γ)198Au reaction. The measured results are compared with literature values and discussed.

Characterization of Irradiation Sites of Apsara Reactor for $k_{0}$-Based IM-NAA and Its Validation and Application

Three irradiation positions of Apsara reactor were characterized by determining epithermal neutron spectrum shape factor <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(\alpha)$</tex></formula> and sub-cadmium to epithermal neutron flux ratio <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(f)$</tex> </formula> for <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm k}_{0}$</tex> </formula> -based Internal Monostandard Neutron Activation Analysis (IM-NAA). The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\alpha$</tex></formula> values were determined by cadmium ratio method using six neutron flux monitors (In, Au, Co, Mo, Zn and Zr). The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f$</tex> </formula> -value was also determined by cadmium ratio method using an Au monitor. The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\alpha$</tex></formula> values of two irradiation positions are found to be positive, which indicated softened epithermal neutron spectra whereas <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\alpha$</tex> </formula> value of the third one is negative indicating hardened neutron spectrum. IAEA reference material, RM SL-1 (Lake Sediment) was analyzed by IM-NAA using experimentally determined <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\alpha$</tex></formula> values of all three irradiation positions. A total of 16 elemental concentrations were determined using Sc as the internal monostandard and the values are found to be in good agreement with respect to the certified or information values. As an application of IM-NAA, two ceramic archaeological samples along with one soil sample were analyzed using Sc as the monostandard.

Measurement of thermal neutron cross section and resonance integral for the 170Er(n, γ)171Er reaction by using a gold monitor

The thermal neutron cross section (σ0) and the resonance integral (I0) of the reaction 170Er(n,γ)171Er were measured by an activation method using a reaction 197Au(n,γ)198Au as a single comparator. The high-purity natural erbium (natEr) and gold (197Au) foils with and without Cd cover with the thickness of 0.5mm were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the activated foils were measured with a well calibrated coaxial HPGe detector. The thermal neutron cross section for the 170Er(n,γ)171Er reaction has been determined to be σ0=7.80±0.35 barn, relative to the reference value of 98.65±0.09 barn for the 197Au(n,γ)198Au reaction. By assuming the cadmium cut-off energy of 0.55eV, the resonance integral for the 170Er(n,γ)171Er reaction is I0=40.4±2.8 barn, which is determined relative to the reference value of 1550±28 barn for the 197Au(n,γ)198Au reaction. In order to improve the accuracy of the experimental results the epithermal neutron spectrum shape factor (α) was determined, and the necessary corrections for the counting loss caused by γ-ray attenuation (Fg), the thermal neutron shelf-shielding (Gth), the resonance neutron self-shielding (Gepi) effects, the γ-ray coincidence summing effect, as well as neutron flux fluctuation. The present results are compared with the reference data and discussed.

Neutron spectrometry with He-3 proportional counters

Helium filled proportional counters are widely used in the field of neutron detection and spectrometry. A review of some parameters and physical effects that influence the He-3 proportional counters response is presented through the experimental study of a commercially available counter. The impact of these effects is taken into account in the description of detector performance when the response is calculated with the Monte Carlo method. A method to determine neutron energy distribution with a bare He-3 counter in an unknown neutron field is presented. The neutron energy range extends up to about 7 MeV. The method does not require a hypothesis about neutron spectrum shape. It is based in the calculated counter response with Geant4, the validity of which is experimentally verified. A detailed description of the steps needed is presented.

Photoneutrons from a beryllium reflector: a potential source of problems with Zr-Au flux monitors in k0 standardization based neutron activation analysis.

The assumption that the shape of the epithermal neutron spectrum can be described, in any research reactor, by the 1/E 1+α function is a fundamental starting point of the k 0 standardization. This assumption may be questioned from a reactor physics viewpoint. The type of moderator, the existence of neutron reflectors, the additional production of (γ, n) neutrons and resonance capture by construction materials may be different for each reactor, with consequences for the shape of the neutron spectrum. This dependency may explain that various practitioners reported contradicting experiences with the use of Zr–Au flux monitors for the determination of the α-parameter. An objective view on the influence of the design of the reactor and irradiation facility on the shape of the neutron spectrum can be obtained by modeling. This has been applied in the Reactor Institute Delft for reactor configurations in which the irradiation facilities face the fuel elements with the presence of beryllium reflector elements. The Monte Carlo calculations indicate a distortion of the 1/E 1+α relationship at the higher energy edge of the epithermal neutron spectrum. This distortion is attributed to the formation and thermalisation of both photoneutrons and (n, 2n) produced fast neutrons in the beryllium, and has a direct impact on the resonance activation of 95Zr, other than represented by the 1/E 1+α function. The obtained relationship between neutron flux and neutron energy was also used for estimating the f-value and compared with the value obtained by the Delft Cr–Mo–Au flux monitor.

Measurement of thermal neutron cross-section and resonance integral for the 165Ho(n,γ) 166gHo reaction using electron linac-based neutron source

The thermal neutron cross-section and the resonance integral of the 165Ho(n,γ) 166gHo reaction have been measured by the activation method using a 197Au(n,γ) 198Au monitor reaction as a single comparator. The high-purity natural Ho and Au foils with and without a cadmium shield case of 0.5 mm thickness were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the activated foils were measured with a calibrated p-type high-purity Ge detector. The correction factors for the γ-ray attenuation ( F g), the thermal neutron self-shielding ( G th), the resonance neutron self-shielding ( G epi) effects, and the epithermal neutron spectrum shape factor ( α) were taken into account. The thermal neutron cross-section for the 165Ho(n,γ) 166gHo reaction has been determined to be 59.7 ± 2.5 barn, relative to the reference value of 98.65 ± 0.09 barn for the 197Au(n,γ) 198Au reaction. By assuming the cadmium cut-off energy of 0.55 eV, the resonance integral for the 165Ho(n,γ) 166gHo reaction is 671 ± 47 barn, which is determined relative to the reference value of 1550 ± 28 barn for the 197Au(n,γ) 198Au reaction. The present results are, in general, good agreement with most of the previously reported data within uncertainty limits.

Experimental evaluation of neutron performance in boron-doped low activation concrete

Reaction rate distribution in concrete with/without boron dopant up to a thickness of 60 cm was measured using Yayoi fast reactor located at University of Tokyo. The 7 reaction rates such as (197)Au(n,gamma), (59)Co(n,gamma), (115)In(n,n'), (55)Mn(n,gamma), (23)Na(n,gamma), (94)Zr(n,gamma) and (96)Zr(n,gamma) were measured at 12 different depths, and the reduction of the reaction rate as a result of boron doping was quantitatively analysed. These reaction rates were also used to determine epithermal neutron spectrum shape parameter. Monte Carlo simulations of the experimental setup were performed using the MCNP-5 code. Simulated depth profiles of reaction rates and the epithermal neutron spectrum shape parameter agreed with the experimental results with fair accuracy. This experimental results provide useful data to benchmark the accuracy of neutron transport codes in the prediction of transmission and neutron spectrum distortion in boron-doped concrete.

Accelerator Experiments on Source Term and Radiation Shielding Performed by Japan Atomic Energy Agency

Three accelerator experiments on source term and radiation shielding performed by the staffs of Japan Atomic Energy Agency (JAEA) to validate the accuracy of the radiation behavior simulation code PHITS (Particle and Heavy Ion Transport code System) are reviewed. In the measurement of neutron spectra from a thin beryllium target bombarded with ˜10-MeV protons, measured peak energies and values of the cross section were the same as those in the Evaluated Nuclear Data File ENDF/B-VII. In the measurements of forward-direction neutron spectra from thick targets bombarded with 140-, 250-, and 350-MeV protons, the calculated spectra from an iron target by the PHITS code agreed well with the measured spectra. In the measurement of neutron spectra from a tungsten target bombarded with ˜400-MeV protons, the shape of neutron spectra and its intensity are compared with that in Los Alamos Neutron Science Center/Weapons Neutron Research.