Otohiko Aizawa

Remodeling and dosimetry on the neutron irradiation facility of the Musashi Institute of Technology reactor for boron neutron capture therapy

The remodeling of the neutron irradiation facility of the Musashi Institute of Technology reactor (TRIGA Mark II, 100 kW) was carried out for the purpose of boron neutron capture therapy. The gamma contamination was reduced by the bismuth scatterer technique, and the thermal-neutron intensity was enlarged by virtue of the cavity effect. A /sup 6/LiF sheet was used instead of a /sup 10/B sheet for neutron collimation to minimize production of the secondary gamma rays.

Prompt gamma-ray neutron activation analysis of boron-10 in biological materials

Prompt gamma-ray neutron activation analysis of 10B concentrations in biological samples was carried out using a germanium detector and single crystal silicon filtered neutron beams from the TRIGA-II reactor. The 10B concentrations of biological samples such as tumors, tissues, blood and cultured cells were estimated from calibration curves obtained by using standard samples containing various 10B concentrations. A method of measuring absolute 10B concentrations was also presented.

Head phantom experiment and calculation for boron neutron capture therapy

Head phantom experiments with various neutron beams and calculations were carried out in order to provide useful information for boron neutron capture therapy (BNCT). Thermal neutron beams for thermal neutron capture therapy were used for phantom experiments with various neutron collimator aperture sizes. The filtered beam neutrons of 24 and 144 keV generated with iron and silicon filters were also used to investigate the possible application of BNCT in the treatment of deep-seated cancers. Thermal neutron fluence and induced capture gamma dose distributions within the phantom were calculated with a transport code DOT 3.5 and compared with the experimental results. The results showed that the calculation used was consistent with the experimental results and provided useful information on BNCT. The filtered beam neutron may be very useful for the treatment of deep or widespread cancer, if there were a high power research reactor constructed for this purpose.

Analysis of Differences in Void Coefficient Predictions for Mixed-Oxide—Fueled Tight-Pitch Light Water Reactor Cells

Abstract Analysis of the benchmark problems on the void coefficient of mixed-oxide (MOX)-fueled tight-pitch cells has been performed using the Japanese SRAC code system with the JENDL-3.2 library and the French APOLLO-2 code with the CEA93 library based on JEF-2.2. The benchmark problems have been specified to investigate the physical phenomena occurring during the progressive voidage of MOX-fueled tight-pitch lattices, such as high conversion light water reactor lattices, and to evaluate the impact of nuclear data and calculational methods. Despite the most recently compiled nuclear data libraries and the sophisticated calculation schemes employed in both code systems, the k∞ and void reactivity values obtained by the two code systems show considerable discrepancy especially in the highly voided state. The discrepancy of k∞ values shows an obvious dependence on void fraction and also has been shown to be sensitive to the isotopic composition of plutonium. The observed discrepancies are analyzed by being decomposed into contributing isotopes and reactions and have been shown to be caused by a complicated balance of both negative and positive components, which are mainly attributable to differences in a limited number of isotopes including 239Pu, 241Pu, 16O, and stainless steel.

Analysis of First-Harmonic Eigenvalue Separation Experiments on KUCA Coupled-Core

The first-harmonic eigenvalue separation, the difference between the fundamental and the first order eigen-values of the higher harmonic neutron transport equations, which were measured at the Kyoto University Critical Assembly (KUCA) has been analyzed. A method was proposed to calculate the first order eigenvalue based on the discrete ordinate method. The 3-D effect, energy group effect, mesh size effect, and transport effect were investigated. Among these effects, the transport effect was significant and when it was taken into account, the calculated eigenvalue separation approached the measured value on the KUCA coupled-core.

Improved Monitoring System of Neutron Flux during Boron-Neutron Capture Therapy

Continuous and simultaneous monitoring of neutron flux in the course of a boron-neutron capture operation on a brain tumor has been achieved using a new monitoring system. A silicon surface barrier diode mounted with /sup 6/LiF instead of the previously reported borax is used to sense neutrons. The pulse heights of /sup 3/H and ..cap alpha.. particles from /sup 6/Li(n, ..cap alpha..)/sup 2/H reaction are sufficiently high and well separated from noises due to ..gamma.. rays. The effect of pulse-height reduction due to the radiation damage of the diode thus becomes smaller, permitting continuous monitoring. The relative error of the monitoring is within 2% over 5 hr for a neutron-flux density of 2 x 10/sup 9/ n/cm/sup 2/ sec.

Total Neutron Cross Section of Lead

The total thermal-neutron cross section of natural lead under various physical conditions was measured by the transmission method. It became clear that the total cross section at room temperature previously reported is lower than the present data. The total cross section at 400, 500, and 600/sup 0/C, above the melting point of lead, 327/sup 0/C, was also measured, and the changes in the cross section as a function of temperature were examined, especially near and below the melting point. The data obtained for the randomly oriented polycrystalline state at room temperature were in reasonable agreement with the theoretical values calculated by the THRUSH and UNCLE-TOM codes.

Fast neutron radiography tests at the YAYOI-reactor, university of Tokyo

Fast neutron radiography (FNR) has been jointly studied by the members of neutron radiography laboratories in Japan by using the CR-39 nuclear track detector at the fast neutron source reactor “YAYOI” of the University of Tokyo. Three beam holes installed at the reactor are utilized, whose collimator ratios, LD, are up to 135, and the fast neutron fluxes are more than 106 ncm−2 s−1. Some well-defined FNR images of various types of objects are obtained with a fast neutron fluence of about 1010 n/cm2. Small holes of 0.5 mm in diameter and 10 mm in depth in an acrylic plate are well imaged through 60 mm thickness of iron plate. Hydrocarbon specimens placed behind thick iron plates (30 mm) are clearly imaged. For the ASTM image quality indicators (IQIs for thermal neutron radiography), very thin A1 spacers with 0.05 mm thickness in the SI indicator have been discernible. The scattering component of fast neutrons from object materials does not seriously degrade the resolution of the FNR image.

Dose measuring system for boron neutron capture therapy

Abstract Dose measuring systems for boron neutron capture therapy (BNCT) of brain tumors are presented. The systems are a real-time monitoring system, an integral measuring system and a 10B concentration measuring system. The real-time monitoring with a small PN junction silicon detector made it possible to simultaneously measure the thermal neutron flux and the gamma dose rate in a patient during neutron therapy. Another monitoring of dose equivalents of thermal neutrons and gamma rays was performed with a BGO scintillation detector connected to an optical fiber. The accurate neutron fluence and gamma dose were determined with the integral measurements of the foil activation method and thermoluminescent dosimeters (TLDs) after irradiation. Kerma doses of thermal neutrons and gamma-rays were also measured with the TLD at the same time. Preliminary measurements of 10B concentration in tissue and blood of a patient were carried out by prompt gamma-ray spectroscopy.

Rapid estimation of core-power ratio in coupled-core system by rod drop method

To determine rapidly the core-power ratio in a coupled-core system, a method is proposed on the basis of the control rod drop experiment. A formula of an asymmetrical two-point version was derived to deduce the core-power ratio and subcriticalities of the individual cores. It requires only a familiar measurement technique and tools for the conventional rod drop experiment to apply this formula for the purpose of obtaining these quantities. The present method was applied to the rod drop data measured in coupled-core systems, where the core-power ratio sensitively depended on the rod patterns. The validity of the proposed method was experimentally demonstrated through the comparison between the measured core-power ratios obtained by the present method and that derived from the flux distribution measurement.