Nobuo Sasamoto

An analysis method of gamma-ray pulse-height distributions obtained with a Ge(Li) detector

Abstract A method is proposed for analysis of the gamma-ray pulse-height distribution (PHD) obtained with a Ge(Li) detector, which makes use of a fitting technique based on a nonlinear least-squares method. The successive steps of analysis are thus made from peak search to estimations of gamma-ray peak areas, peak locations, and their errors. Gamma-ray peaks and background continuum are expressed in a Gaussian distribution function; an exponential function is connected smoothly with the Gaussian at a certain point on the low-energy side of a gamma-ray peak, a newly defined Valley Count Function (VCF) expressing the flat-background continuum located between Compton edge and centroid of peak, and a quadratic polynomial expressing the ordinary background continuum. From the results of the analysis obtained with a computational code, it was found that, to obtain meaningful solutions in gamma-ray PHD analysis, the full width at half maximum (fwhm) must contain three or more channels, and the separation between the peaks should be larger than half the fwhm in the analysis of a composed PHD having two peaks. The validity of the method is shown by an analysis of the gamma-ray spectrum of Ta isotopes.

Fundamental Theory of the Direct Integration Method for Solving the Steady-State Integral Transport Equation for Radiation Shielding Calculation

A complete theory of a direct integration method for solving the steady-state integral transport equation in general geometry is presented together with special techniques for an accurate treatment of monoenergetic radiation source and for mitigation of the ray effect. Emphasis is on several characteristic features, which make the method well adapted to shielding calculations. Refs.

Development of shielding design code for synchrotron radiation beam line

Abstract For the purpose of application to shielding design calculation for beam lines of SPring-8, a 8 GeV class synchrotron radiation facility of Japan, a new shielding code, STAC-8, has been developed on the basis of a shielding design code, PHOTON. Preliminary shielding calculation for the pilot beam lines of SPring-8 is performed with STAC-8. Validity of the code is verified by comparing its calculation with those using a Monte Carlo code EGS4 and PHOTON.

Direct Integration Method for Solving the Neutron Transport Equation in Three-Dimensional Geometry

A numerical method is presented for calculating neutron transport problems in three-dimensional (x,y,z) geometry on the basis of a method of direct integration of the integral transport equation. Several new techniques are introduced to the method to make it well adapted to practical neutron transport calculations in three-dimensional geometry. Refs.

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.

SHINE-III : Simple Code for Skyshine Dose Calculation up to 3GeV Neutrons

Skyshine dose at site boundary is considered as one of the most fundamental issues to get approval of constructing nuclear installations. Skyshine conical beam response functions (CBRF) for high energy neutrons up to 3GeV are obtained using NMTC-JAERI and MCNP code. This CBRF is fitted to the four parameters equation. Simple code named SHINE-III using this equation with updated data is developed.

Estimation of Activity and Dose Distributions around a Proton Linac Induced by Beam Spill

In order to estimate if a proton linac with energy of a few GeV is accessible in a few days after continuous operation of a year with the beam spill rate of 1 W/m, Monte Carlo calculations are carried out. The calculations show that the maximum dose equivalent rate caused by the induced radioactivity of the linac is a few hundreds μSv/h at the distance of 30 cm from the surface of the linac after cooling time of a day.

An Improvement of the PALLAS Discrete-Ordinates Transport Code

An improvement in the approximation of the spatial distribution of the source term in the PALLAS discrete-ordinates code by a combination of linear and exponential functions results in a reduction of numerical errors compared with those due to the use of only a linear approximation based on a direct integration method. The results obtained by the improved approximation for one-dimensional radiation transport calculations are compared with those by the PALLAS code with the original linear approximation and by the S/sub N/ code ANISN. For further verification, this improved approximation is applied to two-dimensional neutron transport calculations, in which numerical errors due to the spatial mesh sizes used in the calculations are studied. As a result, it is found that the use of the improved approximation gives reasonable solutions with small numerical errors, irrespective of the spatial mesh size in both one- and two-dimensional PALLAS calculations of radiation transport.

Status on Shielding Design Study for the High-Intensity Proton Accelerator Facility

A project is now in progress for construction of a high intensity proton accelerator facility. Because of its very high performance of beam power and its energy, the facility requires very thick shielding. In order to establish a reasonable shielding, semi-empirical formulas and simplified design codes were mainly adopted, partially backed up by some Monte Carlo methods. Two simplified codes we adopted have been improved for application to higher energy radiation. The present paper reviews the status of the shielding design study of the facility and refers to the requirement of higher energy nuclear data from the viewpoint of an accelerator shielding design.

Gamma-ray energy release in the decay of fission products

Abstract Total disintegration rate, gamma-ray energy release rate and energy spectrum of the fission products of 235 U, 239 Pu, 241 Pu, and 233 U by thermal neutrons, and 235 U, 238 U, 239 Pu and 232 Th by fission spectrum neutrons have been reevaluated as a function of reactor operating times from 10 2 to 10 8 sec after shutdown. Decay scheme data were taken mainly from the Table of Isotopes [1] and fission yields from Meek and Riders 1972 recommendations [2]. Gamma energy releases do not depend strongly on the incident neutron energy, and those for 239 Pu and 241 Pu are much different from that for 235 U. Soon after fission, the present values for burst fission are lower than those of Perkins [3], but agree after 10 4 sec and agree better with the experimental results of Sugarman et al. [4] and Borst [5]. The calculated data are tabulated in detail to facilitate interpolation.