Tadashi Tsujimoto

Development of an apparatus for measuring ground exhalation rates of 222Rn and 220Rn

A field apparatus with a large area ZnS(Ag) scintillator (30 cm × 40 cm) was developed for measuring simultaneously the exhalation rates of 222Rn and 220Rn from the surface of the ground. The system is based on alpha particles emitted from 222Rn, 218Po, 214Po, 220Rn, and 216Po nuclei floating in the air and deposited on the mylar foil or fringe (skirt), which covers the surface of ground. The alpha particles are subsquently counted at 1-min intervals for about 10 min. Setting a detection limit equal to three times the standard deviation of the background count rate, the detection limit of this system corresponds to 140 mBq m−2 s−1 for 220Rn and 6.8 mBq m−2 s−1 for 222Rn. This detection limit of 222Rn, which decreases with time, corresponds to a 30-min sampling.

Preparation of high purity chromium

Abstract The purification of chromium is important in investigations of its true properties. High purity chromium was prepared by overlap floating zone refining in a dry hydrogen atmosphere at about 100 kPa. The purity was estimated from the values of the residual resistivity ratio RRR 4.2K and activation analyses using neutrons, charged particles and γ rays. The concentrations of residual carbon and oxygen were less than 10 ppm for purified chromium, and the highest value of RRR 4.2K was 667 which is higher than previously reported values. The rolling reduction of the purified chromium was over 50% at room temperature, showing a relatively good ductility.

Multielement trace analysis of high purity aluminium by neutron activation

Instrumental neutron activation analysis was applied to multielement trace analysis of high purity aluminium samples. In order to reduce the production of24Na from the matrix, samples were activated by thermal neutron flux of high cadmium ratio. Detection limits of various impurity elements were evaluated. So called “five nine” class standard aluminium samples were analyzed and concentrations of various impurity elements were determined. The analytical results obtained on zone refined aluminium samples showed that zone refining is effective against many elements, such as Na, Cr, Fe, Co, Cu, Ga, As, Br, Ba, La, Ce, Sm, Yb, Lu, Hf, W, Th and U, but not very effective against the element Sc.

Neutron-irradiation effect on the mechanical properties of alumina fiber

This paper describes the neutron irradiation effects on the deterioration of alumina fiber (made by Mitsui Mining Material, Almax), a typical electrical insulation material. The material was irradiated at the research reactor at Kyoto University Research Reactor Institute with a maximum fluence of 5.6×1023 n/m2 (energy: E>0.1 MeV). Tensile strength and tensile modulus of the specimen scarcely changed. Observation with a scanning electron microscope (SEM) and a transmission electron microscope (TEM) did not indicate any changes in crystal or pore structure. However, the Weibull coefficient of tensile strength decreased as the irradiation dose increased. This suggests an increase in the defect size distribution.

A mysterious spot on the outdoor concentration of radon isotopes

Abstract Temporal and spatial distribution of 222 Rn and 220 Rn and their progeny concentrations in the open atmosphere, 222 Rn and 220 Rn exhalation rates, radioactivities in soil and underground water, including some meteorological factors, were measured at a spot of high 222 Rn and 220 Rn concentrations to investigate the source and occurrence mechanism. Hourly mean concentrations of 222 Rn and 220 Rn during August 1993 were about 230 Bq m −3 and 130 Bq m −3 at 1 m above ground surface. Diurnal variations were high at daytime and low at nighttime, which gives an inverse variation compared with the typical variation in the normal environment. 222 Rn concentrations varied quickly in a few minutes and reached a maximum of about 14 kBq m −3 . The maximum daily mean 222 Rn concentration at 5 cm above ground surface was 11 kBq m −3 . Concentrations of 218 Po, 214 Pb, 214 Bi, and 220 Rn progeny were 8∼61 Bqm −3 , 1∼7 Bqm −3 , 0.5∼5 Bq m −3 , and 0.02∼0.14 Bq m −3 , respectively. The equilibrium factor for 222 Rn was estimated to be 0.01∼0.2. The main source of the mysterious spot of high 222 Rn and 220 Rn concentrations was a small but deep channel between the basement of the building and the surrounding soil, and the extremely localized weather condition.

Measurement and analysis of leakage neutron energy spectra around the Kinki University Reactor, UTR-KINKI

The highly sensitive cylindrical multi-moderator type neutron spectrometer was constructed for measurement of low level environmental neutrons. This neutron spectrometer was applied for the determination of leakage neutron energy spectra around the Kinki University Reactor. The analysis of the leakage neutron energy spectra was performed by MCNP Monte Carlo code. From the obtained results, the agreement between the MCNP predictions and the experimentally determined values is fairly good, which indicates the MCNP model is correctly simulating the UTR-KINKI.

Neutron Radiography Application to Ancient Arts

Neutron radiography testing (NRT) has been applied to several ancient relics at Kyoto University Research Reactor and the cyclotron-based facility of Sumitomo Heavy Industries, Ltd. Some of the results are presented with comments on the usage and applicability of NRT. The objects studied are an excavated bronze mirror with four bells (late 5c.A.D. to early 6c.A.D.), an unearthed corroded bronze mirror with cloth (4c.A.D.), unearthed Buddhist sutras in a bronze case (10c.A.D.), a Tibetan unglazed Buddhist statue cushioned with cloth in a copper box with a window and an excavated iron sword conserved and restored (4–5c.A.D.). From comparisons with X-ray radiography testing, it has been found that NRT can well identify the stones located inside the bells and suggest the casting procedure. Moreover, NRT has been found to be remarkably effective for elucidating unobserved organic objects in bronze fine arts.

Characteristics of Neutron Radiography Systems Using Accelerators and a Research Reactor

The equipments for neutron radiography using a 1-MeV Van de Graaff type accelerator and a 18-MeV electron linac of the Radiation Center of Osaka Prefecture (ORC) and Kyoto University Research Reactor (KUR) were set up. The characteristics of neutron beam and the radiographic image qualities with various films available were measured by a Beam Purity Indicator and a Sensitivity Indicator approved by ASTM and a System Image Quality Indicator devised by Barton.

A method for measuring each concentration of β-emitting nuclides mixed in air

Abstract The authors developed a new type of instrument for continuous measurement of each concentration of β-emitters mixed in air. The instrument consists of a series of several unit double cylindri chambers. Air containing cylinder. The space between the outer and the inner cylinder walls serves as the ionizing section. The thickness of the inner cylinder wall for each unit chamber is different from one to another. The concentration of each β-emitter was calculated from the measured ionization current using calibration constants, which were evaluated using both the Monte Carlo calculation and experiment. The following three combinations of nuclides were taken for the study of performance of this type of instrument: 85 Kr with 41 A, 15 O with 13 N, and 3 H with 85 Kr.