[en] A preconcentration method with combined diethyldithiocarbamate (DDTC) and iron (III) was studied for X-ray fluorescence determination of molybdenum in sea water. Ten grams of sodium chloride, one milligram of iron (III) and 10 ml of 10 w/v% sodium acetate buffer were added to 500 ml of sample, which was adjusted to pH 3.0, by adding 3 ml of 2 w/v% DDTC solution. The coprecipitate containing molybdenum was then collected on a membrane filter paper (0.45 μm), dried at room temperature and delivered to the X-ray fluorescence analysis. Limits of detection and lower determination of this method were 0.3 μg/l and 0.9 μg/l, respectively. This method was applied to determination of molybdenum in sea water. The analytical results found by the calibration curve method were in good agreement with those by the standard addition method. The relative standard deviation in respective five determinations of sea water was 2.9 %. It was concluded that the calibration curve method was available for the determination of molybdenum in sea water. (author)

No abstract available

[en] In the detailed analysis of the index dose rate calculation process using the response matrix method that has been carried out so far, it was shown that the fluctuation of the index dose rate during rainfall could be alleviated by applying the nuclear beam spectrum table corresponding to rainfall time to the rainfall increment of the dose rate. Based on the results, the authors examined the timing of introducing a calculation method corresponding to rainfall time in actual real-time monitoring. (A.O.)

[en] When it rains, environmental gamma-ray dose rate increases due to the effects of natural radionuclides contained in rainwater. For this reason, rain sensors and 0.5mm rain-gauges were installed at a monitoring station to confirm the presence or absence of rainfall and rainfall amount in parallel with measurement of the environmental gamma-ray dose rate. However, the environmental gamma-ray dose rate sometimes exceeds the survey level even during a small amount of rainfall that cannot be observed with a 0.5 mm rain-gauge. In addition, there is a problem that the rain sensor is also sensitive to sea salt particles blown up by strong winds from the sea. Therefore, 0.1mm rain-gauges were installed at an Onagawa monitoring station to investigate their availability in monitoring the environmental gamma-ray dose rate. (A.O.)

[en] For dose-rate measurements of γ-rays in air near a nuclear power plant by remote monitoring, the authors present a detailed analysis for the calculation procedure of the indicator dose-rate based on the response matrix method. Gamma spectra from the NaI(Tl) scintillation detector of Environmental Radioactivity Research Institute of Miyagi, Japan, are processed to obtain the RM (Response Matrix) dose-rate. Subtracting the estimated BG (Background) dose-rate yields the indicator dose-rate. Fluctuations due to rainfall effect are remarkable. The authors investigated the cause of the fluctuation and found an inadequacy in nuclear-spectral flux table to be used to calculate the background originating from U-decay series. Using a modified table adequate at rainfall, they succeeded to diminish the fluctuation and to obtain more moderate indicator dose-rates. (S. Ohno)

No abstract available

[en] Gamma-ray dose rate, gamma-ray spectrum and outdoor radon concentration were measured at three sites in the Oshika-Peninsula, Miyagi, Japan. Increase of gamma-ray dose rate by several nGy/h and ²²²Rn concentration by 60 Bq/m³ were observed, when maritime air mass covered the sites in June 19-20, 2008. In addition, count rates of ²¹⁴Pb and ²¹⁴Bi by an NaI(Tl)-detector increased. Meteorological data of wind-direction, wind-speed, temperature, and radiation balance showed that there was an inversion layer by radiation cooling. Considering such circumstances, increases of ²²²Rn concentration and gamma-ray dose rate can be explained by transport of ²²²Rn -rich air mass from hills and mountains by offshore wind. Similar phenomena observed at three sites in the Oshika-Peninsula in September 2-4, 2008. In this period, remarkable differences of ²²²Rn concentration were observed among sites, and the concentration varied from 60 to 213 Bq/m³. The differences might be induced by a different geological condition, spatial distribution of ²²²Rn, and equilibrium condition between parent and daughter nuclides. (author)

[en] The authors processed, using the response matrix method, the spatial gamma-ray spectra measured with NaI(Tl) detectors in the northern part of Miyagi Prefecture during April 2012 and April 2018, after the Fukushima Daiichi Nuclear Power Station accident. They separated the flux density and dose rate of gamma rays due to radiocesium (Cs-134 and -137) derived from the accident, and evaluated the results. They examined the effects of differences in the surrounding environment, the presence or absence of snow, and weathering on the cesium-donated dose rate. The weathering half-life of cesium after considering the physical half-life from the decay rate of the total dose rate of Cs-134 and -137 was calculated at about 15-23 years when the surrounding area was soil and about 7-8 years when the surrounding area was paved. The half-life obtained from Cs-134,137 primary gamma rays (direct rays) when the surrounding area was soil was about 11-12 years, which was shorter than the total dose rate. Combined with the fact that the dose build-up factor of cesium showed an increasing tendency over time, it was suggested that cesium penetrated into soil. (A.O.)

No abstract available

No abstract available