Fumihiro Masukawa

Benchmark calculations of neutron yields and dose equivalent from thick iron target for 52-256 MeV protons

Neutron yields from thick iron target for 52, 113 and 256 MeV protons were calculated by MCNPX and NMTC/JAM, and compared with data measured by Nakamura et al. and Meier et al. [Nucl. Sci. Eng. 102 (1989) 310]. The MCNPX code reproduced the experimental total neutron yields well by a factor of two, except for 15° at 52 MeV. The NMTC/JAM code also reproduced the experimental total neutron yields by a factor of two, except for 7.5° at 113 MeV, and 52 MeV. Shielding calculations were done for ordinary concrete using the above experimental and calculated neutron spectra. The effective dose distributions using the calculated neutron spectra by both codes were in reasonable agreement with those with the experimental spectra by a factor of about two, except for low emission angles at 113 MeV, and 52 MeV. This discrepancy led to the overestimation of the concrete thickness from 30 to 45 cm and could have a great impact on the construction cost of accelerator facilities. A benchmark calculation of dose equivalent distributions in ordinary concrete for 230 MeV protons reported by Siebers et al. was also performed with MCNPX. The calculated results were in good agreement with the experimental data within a factor of three.

Analyses of High Energy Neutron Streaming Experiments Using DUCT-I

Implementing the updated high energy neutron albedo data calculated by the NMTC/JAERI97 and the MCNP-4A with JENDL-3.2 based library, the simplified streaming calculation code was improved to make DUCT-III. It was applied to analyses of the high-energy neutron streaming benchmark experiments. The code satisfactorily reproduced the measured non-threshold reaction rates and the Monte Carlo calculations. As for threshold reactions, however, its reproducibility of the measurement was seen to be poor.

Evaluation of Radioactivity at Accelerator Tunnels for High-Intensity Proton Accelerator Facility

Activation evaluation is one of the most crucial issues for a shielding design of a high-intensity proton accelerator facility. Radioactivity production in air and cooling water in the accelerator tunnels of a 600-MeV linear accelerator, 3-GeV and 50-GeV proton synchrotrons and their beam transport lines was evaluated by multiplying the spectra of protons and neutrons in the tunnels with activation cross section data. The data were evaluated by calculation using the INC/GEM and the LAHET codes, supported by some experimental data.

Benchmark Analyses of Neutron Streaming Experiments for Proton Accelerator Facilities

In order to estimate the accuracy of the various calculation methods for the neutron streaming through a maze and duct in proton accelerator facilities, we performed benchmark analyses using the radiation shielding design codes. As a result of the benchmark analyses, it is concluded that NMTC/MCNP, MCNPX and DUCT-III are applicable to actual calculation of the duct-streaming radiations for J-PARC.

ESTIMATION OF RADIOACTIVITY PRODUCED IN COOLING WATER AT HIGH-INTENSITY PROTON ACCELERATOR FACILITY

Abstract The radioactivity produced in accelerator cooling water was estimated to determine the maintenance scenario of Japan Proton Accelerator Research Complex (J-PARC) accelerators. The PHITS and the MCNPX codes were used to calculate the proton and neutron fluxes in water-cooled accelerator components. The activation cross-section sets of oxygen for high-energy protons and neutrons were evaluated from the available experimental data and theoretically calculated data by the INC/GEM and the LAHET codes. The radioactivity from corrosion products was also estimated by scaling of the measurements at the High Energy Accelerator Research Organization 12 GeV Proton Synchrotron Experiment (KEK-PS) and Los Alamos Meson Physics Facility (LAMPF). The tritium estimation is an acceptable level for disposal to the environment, while short-lived nuclides at the 3-GeV synchrotron may raise the dose rate in the machine room.

Radiation Safety Design of the J-PARC LINAC

The J-PARC LINAC accelerated the H-minus beam up to the energy of 181 MeV, which is the design value, on January 24th, and got the official license for the beam operation on February 27th, 2007. The beam losses are enough small that the detectable radiation leaks to the working area can be scarcely observed, while the inevitable activation of the beam-line components start slowly. In this paper, we briefly report the method used in the radiation shielding calculation of the J-PARC LINAC.

Validity of the Four-Parameter Empirical Formula in Approximating the Response Functions for Gamma-ray, Neutron, and Secondary Gamma-ray Skyshine Analyses

A four-parameter approximating formula, R=A e a x b f(x), accurately represents the skyshine line beam response function (LBRF) as a function of the distance (x) of the source-to-detector separation. Here, A is a constant for a given source energy and f(x)=e cx x dx is a damping factor. The four parameters are obtained as follows. 1. The value of parameter a corresponds to that of the LBRF at x=1 meter, which is the result of integrating the basic dose spectrum due to a single scattering particle from an emitted beam for a specified angle and a specified source energy. 2. The value of parameter b corresponds to the slope of a straight line of the response function, log R vs. log x, in the range of small distance from a source, where a single scattering particle dominates. 3. The damping factor (f (x)) represents the attenuation trend of the LBRF at distances far from the source; the values of parameters c and d control the quantity of attenuation. The necessary reference LBRF data for point mono-directional photon source energies ranging from 0.1 to 10MeV were generated using the EGS4 Monte Carlo code at 20 emission angles from 0.0 to 180° for 24 source-detector distances up to 2,000 m. The validity of using the four-parameter formula to interpolate the LBRF in the source-to-detector distance, in the emitted angle, and in the energy was also ascertained. Furthermore, this formula was applied to the skyshine conical beam response function (CBRF) for a neutron and an associated secondary gamma-ray with the source energy ranged from thermal to 3 GeV. It was ascertained that the CBRF could be accurately approximated by an interpolation of the fitting parameters at an arbitrary distance and emitted cosine angle.