[en] The thermoluminescence response to neutrons and γ-rays has been measured in an attempt to investigate the high dose and LET effects by thermal neutrons on thermoluminescence phenomena. Glow curves of the undoped LiF have two main peaks at 150⁰C and 335⁰C. These two peaks show different responses to dose and type of irradiation. Superlinear responses are shown in the 335⁰C glow peaks to both γ and neutron irradiation. To explain these responses a model is presented which assumes the production of a two carriers trap center connected with the 335⁰C glow peak in addition to the usual one carrier trap center which corresponds to the 150⁰C glow peak. The mathematical formula derived from this model gives reasonable agreement with the experimental response curves. (author)

[en] 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 ⁶LiF instead of the previously reported borax is used to sense neutrons. The pulse heights of ³H and α particles from ⁶Li(n, α)²H reaction are sufficiently high and well separated from noises due to γ 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 10⁹ n/cm² sec

[en] The absorbed doses in the tumor and in the brain of a patient treated by boron neutron capture therapy are determined by the neutron fluence and the concentration of boron-10 in the tumor and in the blood. In the past the authors used a gold foil activation method to determine the neutron fluence. This method has the drawback that the exact neutron fluence can be determined only after the irradiation is over. They developed in 1977 a system for simultaneous monitorig of thermal neutron flux during irradiation of the patient. Although they reported this in 1978, further advances have been made. They also report briefly on the measurement of boron-10 concentration in tissues. The neutron intensity in the brain is influenced by many factors, such as the distance between the patient's heat and the irradiation port, the size of the irradiation field, and the depth of the tumor. They developed a small detector for simultaneous monitoring which can be implanted into the brain of the patient

[en] The dependence of effective cross sections of gold and uranium for neutron spectrum in Rikkyo University Reactor (TRIGA Mark- II, RUR) fuel cell was studied using computer calculations. The dependence of thermal neutron spectrum with temperature was also investigated. The effective cross section of gold in water of the fuel cell at 32degC was 90.3 barn and the fission cross section of U-235, 483 barn. These two values are similar to the cross sections for neutron energy of 0.034 eV. (author)

[en] The shielding performance of heavy concrete for neutrons and gamma rays was measured experimentally and compared with theoretical predictions. It was found that the hydrogen content in concrete sensitively determined the neutron shielding performance. On the contrary, the gamma ray shielding performance was easily predicted, if the density of concrete and its rough ingredients were given. The shielding performance of heavy concrete can be predicted more accurately, if the hydrogen atom density is carefully analyzed. A very preliminary results to analyze hydrogen atoms using the neutron capture gamma ray will also be discussed. (author)

[en] A simultaneous monitoring device of neutron flux for boron-neutron capture therapy has been developed. A silicon surface-barrier detector mounted with borax is used to count neutrons. The silicon detector is 2.5 mm in diameter and is attached to a cable 1.6 mm in diameter and about 1 m in length. The relative error of the linearity between the counting rate and the neutron flux is within 5%, including statistical fluctuations. The relative error of counting rate is within 5% during 240 min of irradiation with a constant neutron flux of 1.7 x 10⁹ n/cm² sec

[en] The effects of magnesium dopants on glow curve and emission spectra were studied in LiF powders. The intensity of the dosimetric glow peak increased with the amount of magnesium. The emission spectrum of the dosimetric glow peak was determined by using optical interference filters and an unfolding calculation. Four emission bands were identified with peak energies at 2.15, 2.66, 3.00 and 3.53 eV. The relative intensity of the 3.00 eV peak increased with the amount of magnesium. On the other hand the 3.53 eV peak decreased with magnesium amount. Both glow curve and emission spectra are influenced by magnesium impurities. TL centres in our LiF samples are considered to be the complex where trapping and emission centres are combined around the magnesium ions. (author)

[en] Studies on fuel failure detection have been made since 1986 in Rikkyo Research Reactor. One of the methods is the monitoring of the trace concentration of fission products appearing in the air on the surface of the water tank of the reactor. The interested radionuclides here are ⁸⁹Rb and ¹³⁸Cs, which are the daughter nuclides of the FP rare gas nuclides, ⁸⁹Kr and ¹³⁸Xe, respectively and have the half lives of 15.2 min and 32.2 min respectively. They are detected on a filter paper attached on a conventional dust sampler, by sucking the air of the surface of the water for 15 ∼ 30 min during reactor operation (100 kW). In this presentation are reported the results of an attempt to increase the sensitivity of detecting these nuclides by introducing nitrogen gas bubbles into the water. The bubbling of the gas increased the sensitivity as much as several times compared with the case without bubbling. These measurements are giving us the 'background' concentration, the order of which is almost unchanged for these several years, --in 10^-6 Bq/cm³. The origin of these nuclides is considered to be not from the fuel but from the uranium contained as an impurity in the reactor material in the core. (author)

[en] By irradiation of neutrons for the period longer than one month, activation experiment of concrete constituents are performed ,and activated nuclides are analyzed with gamma ray counting. The elements which has very small density (trace element) of ppm order, such as Co, Sc, Cs, Eu, Ce, etc. are successfully identified and their contents are also obtained quantitatively. Activation calculation for concrete constituents was performed with ORIGEN2-82 computer code. It was concluded that radioactivity from the trace elements in reactor shielding concrete plays the important role after a long cooling time. (author)

[en] Boron neutron capture therapy is based on the irradiation of charged particles in the tumour cells. The dose in the tumour is equal to the total energy from the ¹⁰B(n,α)⁷ Li reaction, which is proportional to the product of the neutron fluence and the ¹⁰B concentration in the tumour. Dosimetry for medical therapy implies the monitoring of the neutron fluence and the measurement of ¹⁰B concentrations. The neutron fluence was determined by miniaturized silicon detectors covered with ⁶LiF. The detectors are manufactured in our laboratory and have been successfully utilized for clinical purposes. The ¹⁰B concentrations have, up to now, been measured by chemical analysis. Another measuring system is being studied for practical application. In this system the 0.48 MeV prompt gamma rays emitted from ⁷Li nuclei are detected by Ge(Li) gamma detectors. Errors are 3% for 30 ppm of ¹⁰B and 30% for 1 ppm of ¹⁰B when the sample volume is 0.28 cm³ and the counting time is 1000 seconds. Some clinical results of the boron neutron capture therapy are also described. (author)