Hiroshi Yashima

Reaction Rate Analysis of Nuclear Spallation Reactions Generated by 150, 190, and 235MeV Protons

At the National Cancer Center, proton irradiation experiments have been conducted using the cyclotron accelerator to measure the neutron spectrum by the foil activation method. The experimental results demonstrate that high-energy neutrons are bombarded by injecting high-energy protons onto the tungsten target. The agreement between the results of the experiments and the MCNPX calculations with ENDF/B-VI is around 20% in the relative difference of the C/E (calculation/experiment) values in some of the 209Bi(n, xn)210-x Bi reactions. Here, the activation foil 209Bi is useful in obtaining experimental neutron spectrum information on nuclear spallation reactions of the tungsten target by the high-energy protons ranging between 150 and 235MeV. The current experimental data could contribute to evaluating the accuracy of the numerical simulation methodology of reaction rates and the uncertainties of cross sections of 209Bi, as experimental benchmarks.

Experimental studies of shielding and irradiation effects at high-energy accelerator facilities

Abstract Experimental studies of shielding and radiation effects are carried out at Fermi National Accelerator Laboratory (FNAL) under collaboration between FNAL and Japan, aiming at benchmarking simulation codes and studying irradiation effects for the upgrade and design of new high-energy accelerator facilities. The purposes of this collaboration are (a) acquisition of shielding data in a proton beam energy region above 100 GeV, (b) further evaluation of predictive accuracy of the PHITS and MARS codes, (c) modification of physics models and data in these codes if needed, (d) characterization of radiation fields for studies of radiation effects, and (e) development of a code module for an improved description of radiation effects. The first campaign of the experiment was carried out at the Pbar target station and NuMI experimental station at FNAL, which use irradiation of targets with 120-GeV protons for antiproton and neutrino production, respectively. The generated secondary particles passing through steel, concrete, and rock were measured by activation methods as well as by other detectors such as a scintillator with a veto counter, phoswich detector, and a Bonner ball counter on trial. Preliminary experimental and calculated results are presented.

Neutron Dosimetry in Quasi-Monoenergetic Fields of 244 and 387 MeV

This paper describes the results of neutron spectrometry and dose measurements using a Bonner Sphere Spectrometer (BSS) at the ring cyclotron facility of the Research Center for Nuclear Physics (RCNP), Osaka University, Japan. Quasi-monoenergetic neutron fields were generated using the 7Li (p,n)7Be reaction and 246 and 389 MeV protons. Neutrons produced at 0° and 30° emission angles were extracted into a time-of-flight (TOF) tunnel, and the energy spectra were measured at a distance of 35 m from the target. To deduce the corresponding neutron spectra from thermal to the nominal maximum energy, the BSS data were unfolded using the MSANDB code and response functions were calculated by Monte Carlo (MC) methods. These spectra are compared to spectral measurements using NE213 organic liquid scintillators applying the TOF method. The results are discussed in terms of ambient dose equivalent H* (10) and compared with the readings of other instruments operated during the experiment.

BENCHMARK EXPERIMENT OF NEUTRON PENETRATION THROUGH IRON AND CONCRETE SHIELDS FOR HUNDREDS-OF-MeV QUASI-MONOENERGETIC NEUTRONS-II: MEASUREMENTS OF NEUTRON SPECTRUM BY AN ORGANIC LIQUID SCINTILLATOR

Abstract A shielding benchmark experiment has been performed to obtain the spectra of neutrons penetrating 10- to 100-cm-thick iron shields and 25- to 200-cm-thick concrete shields and to investigate the accuracy of various calculation codes using a 137-MeV quasi-monoenergetic neutron source. The source neutrons are produced from a 1.0-cm-thick lithium target bombarded with 140-MeV protons, and the energy spectra are measured with the time-of-flight (TOF) method using a NE213 organic liquid scintillator. The neutrons emitted in the forward direction were collimated with a 150-cm-thick iron collimator with 10- × 12-cm aperture. TOF and unfolding methods are applied to obtain the energy spectra behind the shield for the peak energy region and continuous-energy region, respectively. Monte Carlo calculations with PHITS and MCNPX are compared with the measured data. The comparison shows that the calculated spectra are in good agreement with the measured spectra.

Benchmark Experiment of Neutron Penetration through Iron and Concrete Shields for Hundreds-of-MeV Quasi-Monoenergetic Neutrons—I: Measurements of Neutron Spectrum by a Multimoderator Spectrometer

Abstract A shielding benchmark experiment has been performed to obtain the experimental data of neutrons penetrated through iron and concrete shields by using 140-, 250-, and 350-MeV p-Li quasi-monoenergetic neutrons. The quasi-monoenergetic neutrons were emitted from a 1-cm-thick Li target bombarded with 140-, 250-, and 350-MeV protons. The neutrons emitted in the forward direction were extracted into the time-of-flight room through a collimator of 12- × 10-cm aperture embedded in a 150-cm-thick concrete wall. The concrete and iron shield blocks were set at the exit of the collimator. Neutron energy spectra behind the shields were measured by a multimoderator spectrometer (3He proportional counter covered with polyethylene moderator of various thicknesses). Neutron energy spectra behind concrete and iron shields with different thicknesses were obtained down to thermal energy. The experimental results were compared with calculation results by the Monte Carlo simulation code PHITS. These experimental results will be useful as benchmark data to investigate the accuracy of various transport calculation codes.

Calibration of a Bonner sphere spectrometer in quasi-monoenergetic neutron fields of 244 and 387 MeV

This paper describes the results of calibration measurements for a Bonner sphere spectrometer (BSS) with 3He proportional counter performed in quasi-monoenergetic neutron fields at the Research Center for Nuclear Physics (RCNP) at the University of Osaka, Japan. Using 246 MeV and 389 MeV proton beams, neutron fields with nominal peak energies of 244 MeV and 387 MeV were generated via 7Li(p,n)7Be reactions. At high energies, the neutron spectra were measured by means of the time-of-flight (TOF) method. The low-energy part of the neutron spectra were determined by BSS measurements down to thermal energies using the MSANDB unfolding code and three different sets of response functions. These were obtained by means of Monte Carlo (MC) calculations including various codes and intra-nuclear cascade (INC) models. Unfolded BSS fluence rates were additionally confirmed by GEANT4 calculations. For calibration of the BSS, measured count rates were corrected for low-energy contributions and compared with count rates calculated using TOF data and various response functions. In addition, measured response values were compared with mono-energetic response calculations, and best agreement was found with GEANT4 results using the Bertini INC model.

Measurements of the neutron activation cross sections for Bi and Co at 386 MeV.

Neutron activation cross sections for Bi and Co at 386 MeV were measured by activation method. A quasi-monoenergetic neutron beam was produced using the (7)Li(p,n) reaction. The energy spectrum of these neutrons has a high-energy peak (386 MeV) and a low-energy tail. Two neutron beams, 0° and 25° from the proton beam axis, were used for sample irradiation, enabling a correction for the contribution of the low-energy neutrons. The neutron-induced activation cross sections were estimated by subtracting the reaction rates of irradiated samples for 25° irradiation from those of 0° irradiation. The measured cross sections were compared with the findings of other studies, evaluated in relation to nuclear data files and the calculated data by Particle and Heavy Ion Transport code System code.

Measurement of neutron activation cross sections for major elements of water, air and soil between 30 and 70 MeV

Neutron activation cross sections between 30 and 70 MeV were measured by the activation method using a semi-monoenergetic neutron field settled at the AVF cyclotron of the Cyclotron and Radioisotope Center(CYRIC), Tohoku University. Natural samples of N, O, Si, Na, Ca and Mg which are the major elements of water, air and soil were irradiated in this neutron field generated through the 7Li(p,n)7Be reaction by 30, 35,40, 50,60 and 70 MeV protons on thin Li target. Neutron yields were measured with the time-of-flight method using a calibrated NE213 organic liquid scintillator. From the induced activities measured with the HPGe detectors, we estimated the excitation functions of 15 cross sections.

Measurement of Angular-Dependent Neutron Production with 140-MeV Protons

Abstract Neutron energy spectra at 90 deg produced from stopping-length graphite, aluminum, iron, and lead targets and at 180 deg produced from a thin lithium target bombarded with 140-MeV protons were measured in the irradiation room of the neutron time-of-flight (TOF) course at the Research Center of Nuclear Physics of Osaka University. The neutron energy spectra were obtained by using the TOF technique in the energy range from 10 MeV to the incident proton energy of 140 MeV. The experimental data for a thick target at 90 deg were compared with calculations performed with the Particle and Heavy Ion Transport code System (PHITS) using the evaluated nuclear data. It was shown that PHITS using the evaluated nuclear data is able to reproduce the secondary neutron spectra at 90 deg. The experimental data for a thin target at 180 deg were compared with calculations using the nuclear physics models in PHITS and the Monte Carlo N-Particle eXtended code (MCNPX). We found that the two codes work well at 180 deg in the neutron energy region above 10 MeV.

Projectile Dependency of Radioactivities of Spallation Products Induced in Copper

The radioactivities of spallation products in a Cu target were obtained by bombarding 230 and 100 MeV/nucleon Ne, C, He, p ions. Irradiation experiments were performed at the HIMAC (Heavy Ion Medical Accelerator in Chiba) facility, National Institute of Radiological Sciences. The gamma-ray spectra from irradiated samples were measured with a HPGe detector. From the gamma-ray spectra, we obtained the variation of radioactivities of nuclides produced in Cu sample with Cu target thickness and the mass-yield distribution of nuclides produced in Cu sample on the surface of Cu target. The results showed that the dependence of the cross sections on the projectile mass strongly depends on the mass number difference between Cu and produced nuclide.