Investigation of radon and thoron concentrations in a landmark skyscraper in Tokyo

The temporal variation of the radon concentration, and the radon and thoron concentrations every three months for a year were measured using two types of devices in a landmark skyscraper, the Tokyo Metropolitan Government Daiichi Building. In the measurement of temporal variation of the radon concentration using a pulse type ionization chamber, the average radon concentration was 21 ± 13 Bq m-3 (2 - 68 Bq m-3). The measured indoor radon concentration had a strong relationship with the operation of the mechanical ventilation system and the activities of the office workers. The radon concentration also increased together with temperature. Other environmentalparameters, such as air pressure and relative humidity, were not related to the radon concentration. In the long-term measurements using a passive radon and thoron discriminative monitor, no seasonal variation was observed. The annual average concentrations of radon and thoron were 16 ± 8 Bq m-3 and 16 ± 7 Bq m-3, respectively. There was also no relationship between the two concentrations. The annual average effective dose for office workers in this skyscraper was estimated to be 0.08 mSv y-1 for 2000 working hours per year. When considering the indoor radon exposure received from their residential dwellings using the annual mean radon concentration indoors in Japan (15.5 Bq m-3), the annual average effective dose was estimated to be 0.37 mSv y-1. This value was 31 % of the worldwide average annual effective dose

Measurement of radon and thoron concentrations in the Tokyo Metropolitan University Arakawa Campus building

Smoking and radon inhalation are the primary causes of lung cancer in many countries. The world average annual dose due to radon inhalation is 1.26 mSv y^, which is more than half of the annual exposure dose from natural radiation sources, 2.40 mSv y^. In this study, radon and thoron radioactivity concentrations（ hereafter referred to simply as concentrations） measurements were carried out in the Tokyo Metropolitan University Arakawa Campus building using a pulse type ionization chamber and passive radon and thoron discriminative monitors. The respective average （±σ） radon concentrations （Bq m^） for each day of the week from Sunday to Saturday were: 21 ± 7, 20 ± 7, 20 ± 8, 22 ± 6, 21 ± 7, 20 ± 6, 23 ± 7. On week days, the radon concentration peaked daily at 8:00 am with a value of 25 ±6 Bq m^, it decreased until 7:00 pm reaching a value of 17 ±7 Bq m^, and then, showed a rising trend to the next morning’s peak. Radon concentration tended to show a higher value and less fluctuation on weekends. No seasonal change was observed. No correlation was observed between radon concentration and thoron concentration. In Japan, the repor ted arithmetic average radon concentration indoors is 15.5 Bq m^ and the arithmetic average concentration outdoors is 5.4 Bq m^. The annual effective dose of radon by inhalation in Japan is 0.64 mSv y^. The average radon concentration of reinforced concrete buildings tends to be higher, though a radon concentration survey in reinforced concrete buildings in Japan is lacking. Calculated annual average exposure dose in the campus reinforced concrete building was 0.15 mSv y^. Annual average exposure dose considering an indoor environment other than the Arakawa Campus building was 0.42 mSv y^

Contribution ratios of natural radionuclides to ambient dose rate in air after the Fukushima Daiichi Nuclear Power Plant Accident

It is important that the contribution ratio of natural radioactivity to ambient dose rate in air is clarified after the accident at the Fukushima Daiichi Nuclear Power Plant. In this study, ambient dose rates in air were observed at 34 places in eastern Japan and the contribution ratios were clarified. The mean contribution ratio of the natural radionuclides was 71% (range: 0–100%). In most places, the natural radionuclides made a larger contribution to the ambient dose rate in air

Changes of ambient gamma-ray dose rate in Katsushika Ward, metropolitan Tokyo before and after the Fukushima Daiichi Nuclear Power Plant Accident

Katsushika Ward in the eastern part of metropolitan Tokyo was the Tokyo area with the highest deposition of artificial radionuclides after the nuclear accident at the Fukushima Daiichi Nuclear Power Plant. A car-borne survey of the air kerma rate was conducted for all of the ward and the results were compared with measurements done in 2005. The mean air kerma rate in 2014 was 59 ± 12 nGy h⁻¹ and that was 50% higher than the rate in 2005 (p < 0.01). Additionally, the environmental half-life was estimated to be 1.9 years from the transition of ambient equivalent dose rate after the accident for data published by the Katsushika Ward Office

Impact on ambient dose rate in metropolitan Tokyo from the Fukushima Daiichi Nuclear Power Plant accident

A car-borne survey was made in metropolitan Tokyo, Japan, in December 2014 to estimate external dose. This survey was conducted for all municipalities of Tokyo and the results were compared with measurements done in 2003. The ambient dose rate measured in the whole area of Tokyo in December 2014 was 60 nGy h^ (23-142 nGy h^), which was 24% higher than the rate in 2003. Higher dose rates (>70 nGy h^) were observed on the eastern and western ends of Tokyo; furthermore, the contribution ratio from artificial radionuclides (^Cs and ^Cs) to ambient dose rate in eastern Tokyo was twice as high as that of western Tokyo. Based on the measured ambient dose rate, the effective dose rate after the accident was estimated to be 0.45μSv h^ in Tokyo. This value was 22% higher than the value before the accident as of December 2014

Ambient dose rate in Mikurashima Island after the Fukushima Daiichi Nuclear Power Plant accident

No detailed ambient dose rate has been reported, either before or after the Fukushima Daiichi Nuclear Power Plant (F1-NPP) accident, for Mikurashima Island, one of the islands within the authority of the Tokyo Metropolitan Government. Thus, the ambient dose rate on Mikurashima Island was observed 4.5 years after the F1-NPP accident. A car-borne survey and a foot patrol survey of the ambient dose rates were conducted over the entire island using a 3-in × 3-in NaI(Tl) scintillation spectrometer. The average ambient dose rate was 27 nGy h^-1 (12 – 45 nGy h^-1) and a higher dose distribution was observed for the northern and eastern areas of Mikurashima Island. However, the impact from the F1-NPP accident (i.e., the presence of artificial radionuclides) was mainly observed for the mountain area of the island (4 – 9 nGy h^-1; located about the center to south-southeast direction). Based on the measured ambient dose rate, the estimated annual effective dose after the accident was 0.09 mSv y^-1

Estimation of radioactivity in single photon emission computed tomography for sentinel lymph node biopsy in a torso phantom study

Objectives: Number of lymph nodes to be removed are determined from residual counts. Estimating residual radioactivity in lymphatic nodes before a biopsy in advance is useful for reducing surgical operation time. The purpose of this study was to estimate total radioactivity of a small hot spot in single-photon emission computed tomography (SPECT) of a torso phantom. Methods: Cross-calibration study was performed to convert counts in SPECT images to radioactivity. A simulation study was performed to estimate the size of volume of interest (VOI) covering a hot spot corrupted with full width at half maximum (FWHM) between 8 and 16 mm. The estimation of total radioactivity was validated in a torso phantom study using small sources. Results: True radioactivity was approximately equal to integrated values of hot spots using the VOI with a diameter of 40 mm in our simulation study. The difference was less than18% in cases of more than 9.4 kBq. Conclusions: The total radioactivity in small sources simulating a typical sentinel node was estimated from SPECT images using a VOI of 40 mm in a torso phantom study. Because the difference from actual values were less than 10% on average when radioactivities were more than 9.4 kBq, the total radioactivity of a lymph node can be estimated in a clinical examination

Natural Variation of Ambient Dose Rate in Air of Izu-Oshima Island After the Fukushima Daiichi Nuclear Power Plant Accident

The ambient dose rate in air and radioactivity concentration in soil samples collected on Izu-Oshima Island were observed in 2012, 2013 and 2014, i.e., one, two and three years after the severe accident at the Fukushima Daiichi Nuclear Power Plant. A car-borne survey for the ambient dose rate in air was carried out for the entire island. Soil samples were collected for the radioactivity concentration measurements from 22 points. The ambient dose rates in air were 36 nGy h⁻¹ in 2012, 34 nGy h⁻¹ in 2013 and 29 nGy h⁻¹ in 2014, respectively. The corresponding radioactivity concentrations in those years for ¹³⁴Cs were 53 Bq kg⁻¹, 39 Bq kg⁻¹ and 29 Bq kg⁻¹ and for ¹³⁷Cs, 87 Bq kg⁻¹, 73 Bq kg⁻¹ and 75 Bq kg⁻¹. All the values have decreased every year