Terrestrial gamma radiation dose rate in Ryukyu Islands, subtropical region of Japan

Temporal and Spatial Variation of Radon Concentrations in Environmental Water from Okinawa Island, Southwestern Part of Japan

In this study, to get a better understanding in characterizing groundwater and ensure its effective management, the radon concentrations in water samples were measured through Ryukyu limestone in southern Okinawa Island, Japan. Water samples were collected from a limestone cave (Gyokusendo cave, dropping water) and two springs (Ukinju and Komesu, spring water), and the radon concentrations were measured by liquid scintillation counters. The radon concentrations in the samples from the Gyokusendo cave, and Ukinju and Komesu springs were 10 ± 1.3 Bq L⁻¹, 3.2 ± 1.0 Bq L⁻¹, and 3.1 ± 1.1 Bq L⁻¹, respectively. The radon concentrations showed a gradually increasing trend from summer to autumn and decreased during winter. The variation of radon concentrations in the dripping water sample from the Gyokusendo cave showed a lagged response to precipitation changes by approximately 2–3 months. The estimated radon concentrations in the dripping water sample were calculated with the measured radon concentrations from the dripping water obtained during the study period. Based on our results, groundwater in the Gyokusendo cave system was estimated to percolate through the Ryukyu limestone in 7–10 days, and the residence time of groundwater in the soil above Gyokusendo cave was estimated to be approximately 50–80 days. This work makes a valuable contribution to the understanding of groundwater processes in limestone aquifers, which is essential for ensuring groundwater sustainability.

Japanese population dose from natural radiation

The radiation doses from natural radiation sources in Japan are reviewed using the latest knowledge. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the Nuclear Safety Research Association report the annual effective doses from cosmic rays, terrestrial radiation, inhalation, and ingestion as natural sources. In this paper, the total annual effective dose from cosmic-ray exposure is evaluated as 0.29 mSv. The arithmetic mean of the annual effective dose from external exposure to terrestrial radiation is 0.33 mSv for the Japanese population using the data of nationwide surveys by the National Institute of Radiological Sciences. Previously in Japan, although three different groups have conducted nationwide indoor radon surveys using passive-type radon monitors, to date only the Japan Chemical Analysis Center (JCAC) has performed a nationwide radon survey using a unified method for radon measurements conducted indoor, outdoor, and in the workplace. Consequently, the JCAC results are used for the annual effective dose from radon and that for radon inhalation is estimated as 0.50 mSv using a current dose conversion factor. In this paper, UNSCEAR values are used for the mean indoor and outdoor thoron-progeny concentrations, and the annual effective dose from thoron is reported as 0.09 mSv. Thus, the annual effective dose from radon and thoron inhalation is 0.59 mSv. From a JCAC large-scale survey of foodstuffs, the committed effective dose from the main radionuclides in dietary intake is 0.99 mSv. Finally, the Japanese population dose from natural radiation is given as 2.2 mSv, which is similar to the reported global average of 2.4 mSv.

Natural radioactivity-based radiological hazards in soils of the islands: a case study from Eastern Turkey

A comprehensive work was carried out to investigate natural radionuclides of 238U, 232Th and 40K in 73 soil samples collected from islands of Adır, Çarpanak and Akdamar on the Van Lake (Turkey) located at Eastern Turkey. Radioactivity concentrations of these radionuclides were measured by using a gamma spectrometer with NaI(Tl) detector to be from 4.11 to 77.1 Bq/kg, from 6.0 to 70.0 Bq/kg and from 133.05 to 749.77 Bq/kg with the mean values of 33.33 Bq/kg, 36.68 Bq/kg and 478.19 Bq/kg, respectively. In addition, the absorbed gamma dose rate in air (D) and annual effective dose equivalent (AED) were found to be 57.5 nGy/h and 70.5 μSv/year, respectively. We have shown that our results might be related to the geological formation type. The results were compared with some published ones in Turkey and the World, which were found within acceptable limits.