Meteorological parameters contributing to variability in 222Rn activity concentrations in soil gas at a site in Sapporo, Japan.

Continuous (222)Rn monitoring in soil gas since November 22, 2004 has revealed variability in activity concentration with time in the semi-natural woods on the campus of Hokkaido University in Sapporo, Japan. Among various factors affecting soil radon levels and variability, temperature was found to be dominant during three seasons when activity concentrations of (222)Rn showed a diurnal high and nocturnal low with a boundary around 10 o'clock in the morning. This pattern was disturbed by low pressure fronts with occasional rain. The activity gradually decreased as soil temperatures decreased from late November to mid-December. After the ground surface was completely covered with snow, soil radon levels became low with a small fluctuation. There were several peaks of (222)Rn on the time-series chart in winter. Those peaks appearing in early winter and early spring may be interpreted by considering meteorological parameters. In a few cases, the radon activity suddenly increased with increasing pressure in the soil at a depth of 10 cm, which may be associated with subsurface events such as seismic activity in the area.

Variation of (222)Rn activity concentration in soil gas at a site in Sapporo, Japan.

Several factors controlling the soil radon level in the present site were found to be changing air-filled porosity caused by fluctuations in moisture content, differences between the atmospheric and soil temperatures as well as volumetric (226)Ra content of the soil. The radon activity increased significantly in early October, especially at point 1, possibly as a result of a magnitude 8.0 earthquake which occurred on September 26, 2003, with epicenter located offshore near Tokachi, Hokkaido.

Calculation of fluence to dose conversion coefficients in partial exposure.

Organ doses and effective doses of electrons and photons for the partial exposure using the MIRD-5 phantom and EGS-4 Code have been calculated. Irradiation geometries are AP and PA exposure. Calculations are carried out using 5 isocentered beams with different sizes to investigate the beam sizes effect on the effective dose. The results show that the effective doses depend not only on the energy of incident particle but also on the exposure position and the beam size on the body.

Superheated emulsion in neutron spectrometry.

The application of superheated emulsion as a neutron spectrometer is described by varying the operating temperature and the ambient pressure of the emulsion. For the calibration of the detector, a relationship was established between the degree of metastability (ss) of superheated emulsion and the threshold neutron energy. The sensitivity and the integral response of the emulsion was calculated and compared with the experimental results.

Propagation characteristics of neutrons leaking from the accelerator facilities.

In this study spatial and time distribution of neutrons leaking from Hokkaido University 45 MeV Electron Linac facility have measured and compared with the Monte Carlo simulations. The neutron transport processes inside and outside the facility building has been simulated using MCNP. The neutrons have measured by BF3 counters and 3He counters with polyethylene moderators up to the distance of 330 m from the facility. The spatial distribution of ambient dose equivalent converted from the counts has been compared with the simulation. The distribution estimated from the counts by the BF3 counter has been shown fairly good agreement with the calculation. The spatial distribution of counts obtained at the 45 MeV Electron Linac facility has been compared with that obtained at the Fusion Neutronics Source (FNS) facility of JAERI. The difference between the propagation characteristics of neutrons leaking from those facilities has been discussed.

Mesoscale variability of vertical profiles of environmental radionuclides (40K, 226Ra, 210Pb and 137Cs) in temperate forest soils in Germany.

Vertical profiles of environmental radionuclides (40K, 226Ra, 210Pb and 137Cs) were investigated in several temperate forest soils in Germany to estimate heterogeneity of the soil horizon of interest. Absolute values of the activity concentrations of these nuclides varied to a large extent depending on the properties of individual forests as well as local geology. Several trends were generally observed independent of the location: (1) Activity concentrations of 40K increased with increasing soil density reflecting that most potassium is contained in mineral components of the soil. The variations in the 40K activity with depth may relate to biological activities in subsoil, such as root uptake of the nutrients. (2) Profiles of 226Ra with depth could be an indicator for evaluating soil heterogeneity within a horizon of interest. They are also useful to estimate anthropogenic 210Pb (210Pbexc) derived from the atmosphere via dry fallout or wet deposition. In several forests, there appeared surface enrichment of 210Pb down to a depth of approximately 10 cm, in which the 210Pb would have come from the atmosphere by combustion of fossil fuels. (3) Depth profiles of 137Cs were roughly divided into three types in which (a) the activity concentration decreased exponentially with soil depth, (b) small amounts of 137Cs existed only in the upper-most layer of the soil (0-5 cm) and (c) 137Cs disappeared at certain depths and appeared again at deeper portions of the soil. Consequences of bioturbation could be deduced from variability in vertical profiles of the environmental radionuclides. It is probable that a site showing an exponential decrease of the 137Cs activity with depth and also having a surface enrichment of 210Pb is not significantly influenced by bioturbation.

Radiation-chemical properties of the hypoxic cell radiosensitizer doranidazole (PR-350).

This study was performed to confirm the radiation-chemical properties of the 2-nitroimidazole derivative doranidazole, (+/-)-(2RS,3SR)-3-[(2-nitroimdazol-1-yl)-methoxy]butane-1,2,4-triol [CAS 137339-64-1], PR-350, which was synthesized as a hypoxic cell radiosensitizer with low toxicity. Radiation-chemical experiments using doranidazole showed that (1) unlike O2, it had high reactivity toward not only hydrated electrons (eaq-), but also hydroxyl radicals (.OH), (2) the reduced intermediates of doranidasole had no ability to induce immediate strand breaks of colE1 plasmid DNA, (3) doranidazole enhanced radiation-induced DNA strand breaks of colE1 plasmid DNA in the aqueous state, whereas it did not enhance the base alteration, such as 8-oxo-deoxyguanosine, (4) it enhanced the radiation-induced formation of strand breaks with 3'-phosophate and 3'-phosphoglycolate termini, and (5) it was bound to DNA after irradiation. These facts revealed that the majority of radiation-chemical properties of doranidazole, except for the high reactivity toward OH, were similar to those of oxygen.

Investigation of the soil radon variation during the winter months in Sapporo, Japan.

Soil radon was measured from late October 2000 to January 2001 at three test sites on the campus of Hokkaido University in Sapporo, Japan. Factors affecting radon concentrations were investigated with relation to meteorological data, as well as soil 226Ra content, mineral composition, water content, and pH, Eh and conductivity. Soil radon varied with time and with sampling site appreciably, in a manner unaltered by the surface geology. However, the ratio of radon isotopes (220Rn/222Rn) in the soil was constant within each sampling site, regardless of varying concentration of these nuclides during the monitoring period. Snow covering on the soil surfaces may affect the 222Rn concentration.