Toshiso Kosako

Measurements of summer radon and its progeny concentrations along with environmental gamma dose rates in Taiwan

The concentrations of 222Rn (radon) and its progeny with surrounding environmental gamma-dose rates were measured simultaneously inside and outside of buildings at 10 locations around Taipei and Hualien in Taiwan. For summer radon in Taiwan, indoor concentrations were estimated to be about 20 Bq m(-3) with about 90 nSv h- of environmental gamma, and outdoors, about 10 Bq m(-3) with about 70 nSv h(-1). The equilibrium factors were calculated to be 0.2-0.3 indoors and 0.3-0.4 outdoors. Indoor radon concentration had a weak positive correlation with gamma-dose rate. Since there is a possibility that high radon concentrations exist indoors during the cool season in Taiwan because of extremely low ventilation rates in the dwellings, a winter survey in January through February will be needed for future estimation of the annual effective dose.

Europium-152 depth profile of a stone bridge pillar exposed to the Hiroshima atomic bomb: 152Eu activities for analysis of the neutron spectrum

The 152Eu activity depth profile of a granite pillar of the Motoyasu bridge located 132 m from the Hiroshima atomic bomb hypocenter was assessed. The pillars each measured 82 cm in depth, 82 cm in width and 193 cm in height. One of the pillars was bored and 6.8-cm-diameter core samples were removed and cut into 2-cm-thick disks. Two gamma rays of 152Eu, 122 keV and 344 keV, in each disk were measured using a low background, gamma-ray spectrometer, and the activity distribution was determined as a function of depth in the granite. A concentration of stable Eu in the granite was determined by activation analysis. The specific radioactivity of 152Eu and 154Eu at the pillar surface was determined to have been 117 and 24 Bq per mg Eu, respectively, at the time of detonation. The value of 152Eu agrees within 20% of that calculated by Loewe. The depth profile of 152Eu in granite demonstrates a distinct difference from the estimates made only by thermal neutrons. Present data provide valuable information for the analysis of the neutron spectrum of the Hiroshima atomic bomb and its intensity.

Annotated bibliography and discussion of gamma-ray buildup factors

Abstract The literature from 1950 to April 1987 on gamma-ray buildup factors for simple monoenergetic sources and for homogeneous media are surveyed and classified according to the source condition of point isotropic, plane normal, and plane isotropic. Based on those data, discussions have taken place to find out the status and the future issues on gamma-ray buildup factors.

The thin layer activation technique applied to the on-line iron wear measurement of an engine cam nose

Abstract The thin layer activation technique, in which 7 MeV proton beam was irradiating an iron surface to produce a very thin (several tens μm) activated region, was applied to the on-line iron wear measurement of an engine cam nose. The wearing amount of this activated part was measured using a Ge-semiconductor detector in an on-line and nondestructive method. The calibration curve of iron wear was obtained through the comparison of this radiometric method and the usual electromicrometer method in which an iron block wear test is performed by a polishing machine. For the application of this method to a real car engine part (engine cam nose), a data acquisition system was built using microcomputers. The wear characteristics were successfully measured and the effectiveness of this method was verified.

Wear measurement at depths of several tens micrometers on the surface of iron using a thin layer activation method by 7 MeV proton beam

Abstract A method of measuring iron wear using thin layer activation is discussed. The iron surface is activated by a 56Fe(p, n)56Co reaction etc., using a 7.00 MeV proton beam from a tandem Van de Graaff accelerator. Irradiation of 0.5–2 (μA beam currents produces 1–10 μCi of 56Co activities in a layer about 50 (μm thick. To get the basic depth profile of cobalt activities, a 1.5 cm iron cube with a 3 mm diameter activation area is used to produce a wear calibration curve. Wear is produced by a polishing machine and wear thickness is measured by a precise electric micrometer. Monitoring radiation instruments are a 3 in. diameter × 3 in. Nal (Tl) scintillator and a high-purity Ge detector. A detailed iron wear calibration curve using 56Co, 57Co and 58Co activities is obtained in accordance with iron wear thickness. After discussions, a universal iron wear calibration curve using the 56Co/57Co or 56Co/58Co ratio is newly developed. This convenient curve is expressed in an experimental formula with a correction for time attenuation.

Relationship between variations of 7Be, 210Pb and 212Pb concentrations and sub-regional atmospheric transport: Simultaneous observation at distant locations

In order to investigate the applicability of (212)Pb as a tracer for atmospheric transport in the sub-regional scale (few hundred kilometers in horizontal direction and up to approximately 1km by height), we measured the air concentrations of the short-lived radionuclide (212)Pb along with the long-lived (7)Be and (210)Pb near the ground surface. For this purpose, simultaneous observations were continued for several days at three locations: a reference point representative for standard land surface atmosphere conditions, a second location at an altitude 650 m near the reference point, and on a solitary island approximately 180 km from the reference point. Measurements of radioactivity in aerosol particle samples collected at intervals of 2-3h with a high-volume air sampler were performed by extremely low background gamma-ray spectrometry with the use of Ge detectors located at the Ogoya Underground Laboratory. Concentration of (7)Be or (210)Pb and their variation patterns was found to be similar among the three points during the whole observation period except for moment of the passage of a cold front. The results indicate that distributions of concentrations of the long-lived nuclides were uniform in this range. On the other hand, concentration levels and the variation patterns of the short-lived (212)Pb differed greatly from one location to another, reflecting differences in geographical location and altitude of the observation points. Additionally, there were certain indications that observed concentration of (212)Pb contained two components: an autogenous component from sources nearby and a heterogenous one from faraway sources carried by atmospheric horizontal transport. Results of this study provide experimental proof that (212)Pb can be used as a tracer of sub-regional atmospheric transport.

Environmental neutron measurements around nuclear facilities with moderated-type neutron detector.

A cylindrical BF3 counter with cylindrical polyethylene moderators of 1-, 3-, 6- and 10-cm wall thickness were developed for neutron spectrometry, having response functions calculated by the time-dependent multi-group Monte Carlo code, TMMCR, and evaluated by a time-of-flight experiment in the energy region from epithermal to about 50 keV. This system of neutron detectors was used to measure the environmental neutron spectrum and dose equivalent around a 252Cf fission neutron source, a fast neutron source reactor, a cyclotron and an electron synchrotron. The neutron spectrum and dose obtained by this detector system showed very good agreement with those measured by a commercially available neutron rem counter and calculated by our MMCR Monte Carlo code. As a result of these comparisons, this detector system has been established as a standard spectrometer and dosimeter for environmental measurements around nuclear facilities.

Annotated references on neutron and photon production from thick targets bombarded by charged particles

The literature on neutron and photon production from thick targets bombarded by charged particles has been surveyed. The survey covers fourteen journals and some internal reports and conference proceedings, mainly from 1965 up to June 1984. For each paper, applicable information is listed on type and energy of the projectile, the accelerator used, composition and thickness of the target, the experimental method, the calculation, and the quantities obtained. The references on neutron and on photon production are accessed through two indices which list the available projectile-target combinations and the projectile energy range.

Estimation of response functions of moderating type neutron detectors by the time-of-flight method combined with a large lead pile

Abstract The energy dependent response functions of moderating type neutron detectors having cylindrical polyethylene moderators of 1, 3, 6 and 10 cm thicknesses were determined using the time-of-flight (TOF) technique. By combining the 35 MeV electron linear accelerator with a large lead pile of about 150 t, a pulsed neutron field which is rich in intermediate neutrons was formed and its spectrum at the standard measuring point for the TOF experiment was measured by a Li glass scintillator. In this kind of TOF, the neutron time delay in the polyethylene moderator due to multiple collisions with hydrogen was evaluated by the time dependent neutron transport Monte Carlo code, and compiled to the time response matrix. By using the neutron spectrum at the standard measuring point and the time response matrix, the energy dependent response functions of the moderating type neutron detectors were determined from the measured time spectra for the first time in a considerably wide energy range from a few eV to about 50 keV. The experimental response functions showed good agreement with the calculated results.

Applicability of convex hull in multiple detector response space for neutron dose measurements

A novel neutron dose measurement method that flexibly responds to variations in the neutron field is being developed by Japan Atomic Energy Agency. This is an implementation of the multi-detector method (first introduced in 1960s) for neutron dose evaluation using a convex hull in the response space defined for multiple detectors. The convex hull provides a range of possible neutron dose corresponding to the incident neutron spectrum. Feasibility of the method was studied using a simulated response of mixed gas proportional counter. Monochromatic neutrons are shown to be fundamentally suitable for mapping the convex. The convex hull can be further reduced taking into consideration a priori information about physically possible incident neutron spectra, for example, theoretically derived moderated neutron spectra originated from a fission neutron source.