Tomonori Hyodo

Propagation of Errors from Response Functions to Unfolded Spectrum

AbstractAn analysis was made on the propagation of errors from the response functions to the unfolded spectrum in the unfolding process from a pulse height distribution to an energy spectrum. In the derivation of formulas, the terms of high variance were ignored. Assumed errors of the response functions were limited to statistical errors in Monte Carlo calculations for the response functions. The unfolding processes used were the SIMPLE method and the FERDO method. The test calculations were done assuming typical spectra having a sharp peak and the 252Cf fission spectrum. The response errors can have a serious influence on the flux error, especially in the case of a sharply peaked spectrum.

Measurements of neutron and gamma-ray streaming in a cavity-duct system and an analysis by an albedo Monte Carlo method

Spectral and spatial distributions of neutrons and gamma rays were measured in a simple cavity-duct configuration to observe profiles of cavity streaming. The change of the profiles of neutrons and gamma rays is examined by blocking source neutrons with a 32-cm-thick aluminum plug. The following observations resulted from the experiments: Fast neutrons of several million electron volts energy streamed through ducts. The neutron and gamma-ray spectra were similar except in the source neutron beam. The gamma rays were predominantly those arising from neutron capture in iron. The aluminum plug greatly decreased the fast neutron flux but had only a limited effect on the low energy neutron flux. The applicability of the albedo Monte Carlo calculational method to this problem was examined with the following conclusions: For ducts of small radius, the calculations overestimate the streaming because the albedo data were given for plane geometry. Low energy neutrons were underestimated by the calculation due to the neutron penetration through the cavity wall.

Energy spectra transmitted through iron slabs of bremsstrahlung produced in iron and gold targets by 0.5–1.44‐MeV electrons

The bremsstrahlung spectra transmitted through iron slabs were measured as a function of incident electron energy and iron‐slab thickness. In this experiment, the gold and the iron targets were bombarded by 0.5–1.44‐MeV electron beams from the Van de Graaff accelerator. Bremsstrahlung produced in the target and transmitted through the iron slab, which emerged at the forward direction of the incident electron beam, was detected with a NaI(Tl) scintillator. The experimental results were in good agreement with those of the approximate numerical calculation of the forward photon spectra. From the slopes of attenuation curves of total photon number and intensity, the effective attenuation coefficients and the effective energies were obtained as a function of the incident electron energy.

Penetration of secondary neutrons and photons from a graphite assembly exposed to 52-MeV protons

Spectra and attenuation profiles of neutrons and gamma rays transmitted through graphite piles were measured by an organic scintillator with an n-..gamma.. discrimination technique. The neutrons and gamma rays were produced in a graphite target placed in front of the piles, which were bombarded by 52-MeV protons. The piles were 54 cm high, 90 cm wide, and 11.7, 23.5, and 44.9 cm thick. The energy spectra of neutrons and gamma rays were obtained after unfolding by the FERDO code, from pulse-height distributions. Spectra calculated by use of a Monte Carlo neutron transport code developed for neutrons of energy up to 50 MeV show good agreement with the measured spectra. 9 figures, 1 table.

BACKSCATTERING OF GAMMA-RAYS FROM SEMI-INFINITE STRATIFIED SLABS OF ALTERNATING TIN AND ALUMINUM LAYERS.

The backscattering of γ-rays has been investigated from semi-infinite stratified slabs of alternating layers of tin and aluminum. The energy spectrum and the angular distribution of backscattered photons, as well as the number and energy albedos were obtained for 60Co and 137Cs point isotropic sources. They were compared with the data obtained with single layers of tin and aluminum. The stratified slabs of alternating layers were assumed in this study to be equivalent in property to a homogeneous mixture of tin and aluminum, and the effective atomic numbers were computed on this basis. The resulting values are found to agree with the effective atomic numbers corresponding to the albedo values obtained for the alternating layers.

Characteristics of miniature dosimeter developed for measurement of bremsstrahlung

Abstract This report describes characteristics of the miniature dosimeter which was developed for the measurement of the exposure rate of bremsstrahlung and of the absorbed dose. This dosimeter is very easily used without applied bias voltages and is very cheap. It is a silicon diffused n -p + junction device. The silicon detecting element of this dosimeter has the form of a disk, 1.5 mm in diameter and 0.2 mm long, which is covered with 1 mm thick copper. The bremsstrahlung was produced in a gold target bombarded by 0.6–1.8 MeV electron beams from a Van de Graaff accelerator. The radiation-induced current was proportional to the exposure rate of bremsstrahlung over the range of 10 2 –10 6 R/h and was independent of the electron energy incident on the gold target, and of the room temperature. This dosimeter gave a current of (1.40±0.05) × 10 −3 μ A/(R/s). The depletion-layer thickness of this dosimeter and the absorbed dose in the silicon detecting element per roentgen were found by calculation to be approximately 79.0 μm and 1.3 Rad/R. Using these values, we obtained 0.96 Rad as the absorbed dose in silicon per roentgen of bremsstrahlung under charged-particle equilibrium.

Fast Neutron Spectra Transmitted through Iron and Sodium Slabs

Transmitted neutron spectra were measured for Fe slabs of 9.6 and 19.2 cm thick and 1 and 2 canned Na slabs of 15 cm thick (thickness of the stainless-steel can was 3 mm). The neutrons from the core of fast neutron source reactor “YAYOI” of the University of Tokyo were collimated and incident to the slabs. The intensity and the profile of the incident neutron beam was determined by a preliminary experiment. The transmitted neutrons were measured on the collimated axis and polar angle of 30° and 45° to the axis. Point-to-point Monte Carlo calculation was carried out for the purpose of comparison with experimental data. The results of the calculation showed good agreement to the experimental spectra.

Backscattering of Neutrons and Secondary Gamma-Rays from Aluminum and Lead Slabs for 15-MeV Neutrons

To obtain neutron and secondary γ-ray albedos for 15-MeV neutrons, spectral measurements of backscattered neutrons and γ-rays from Al and Pb slabs were carried out for monodirectional beams of D-T neutrons using the associated particle method. In the experiment, an NE-213 scintillator was used for simultaneous measurement of the neutron and photon spectra with the aid of the pulse-shape discrimination technique. The obtained pulse height distributions were unfolded to energy spectra by the FERDO code. The accuracy of the measured spectra was examined using calculated results of the Monte Carlo code which was newly developed for the combined neutron and photon transport calculation. A fairly good agreement was obtained between the measured and calculated results, excluding some discrepancies which seemed to come from the inaccuracy in the cross section data used in the Monte Carlo calculation. The obtained neutron and photon data in this paper are very meaningful for the reference data of the neutron and s...

Transmission of Gamma-Rays from 60Co Monodirectional Source through Slabs of Polyethylene and Iron

Scattered γ-rays were measured with 5-in. diameter by 5-in. long NaI(Tl) scintillator for the purpose of obtaining information on the transmission of 60Co γ-rays incident to polyethylene and iron slabs, and layered combinations thereof. The primary γ-rays were collimated, and the detector was used without collimator. The spectra of scattered γ-rays above 300 keV were quite similar to each other irrespective of material and thickness when the scattering angle and scatterer thickness in mean free path units were normalized.

Transmission of gamma rays through pipe walls

Abstract Transmission of gamma rays from 60 Co and 137 Cs line isotropic sources through a steel pipe wall was measured as a function of the wall thickness. The measurement was carried out with two alternative arrangements: a point isotropic source and a long cylindrical ionization chamber, and also a moving point isotropic source on the pipe axis and a small spherical ionization chamber. Comparing the build-up factor obtained by this experiment with that for similar geometry calculated from the results obtained by Goldstein and Wilkins for an infinite homogeneous medium using the method of moments, the ratio of the former to the latter was 0.90 for 60 Co and 0.87 for 137 Cs, respectively, for the wall thickness larger than 1.5 cm.