Terrestrial Gamma Ray Dose Rates Research Articles

日本列島における地表γ線量率分布の地学的背景

日本列島における地表γ線量率分布の地学的背景

Terrestrial Gamma Ray Dose Rates in the Region from Fuji-Hakone District to the Izu Islands

Terrestrial Gamma Ray Dose Rates in the Region from Fuji-Hakone District to the Izu Islands

Terrestrial Gamma Ray Dose Rates in Granitic Rock Terrains in Japan

Air absorbed dose rates evaluated from uranium, thorium and potassium contents in rock samples (rock dose rate) have been compared with K2O data in order to understand lithologic characteristics of terrestrial γ-ray dose rate levels in granitic rock terrains. The comparison showed that the dose rate increased with increasing K2O content of rock. The crystallization differentiation model of magma was used to analyze this trend quantitatively. Next, data sets were compiled with respect to dose rate measured on soil (soil dose rate) and K2O content of bedrock at the corresponding site. A semi-empirical formula expressing the soil dose rate as a function of K2O content of rock was derived by comparing with the rock dose rate analysis.

Terrestrial Gamma Ray Dose Rates in Dacitic and Rhyolitic Terrains

Air absorbed dose rate data taken at 36 sites have been analyzed in order to understand lithologic characteristics of dose rate levels measured on soils in dacitic and rhyolitic terrains. The dose rate increased with increasing K2O content of rock. The following three models were tested to interpret this trend, i.e., crystallization-differentiation of mafic or felsic magma, partial melting of mafic or felsic material, and mixing of mafic and felsic magmas. Semi-empirical formulas expressing the dose rate as a function of K2O content were derived based on the above models.

歩行サーベイによる空間放射線線量率の測定

In order to estimate the environmental radiation dose rate level, measurements of the terrestrial gamma ray dose rates and cosmic ray ionizing components were conducted in public places such as park, street and train in Tokyo area. Measurements for 10 s with a NaI(Tl) scintillation spectrometer were repeatedly carried out with walking. Terrestrial gamma ray dose rate ranges from 10 nSv/h in a train to 80 nSv/h on the stone road. Although cosmic ray ionizing component was constantly 30 nSv/h in the outdoor, reductions by shielding effect were observed at underground and in the concrete building. Influence of radiopharmaceutical was measured in the stations where so many people exist. This shows that the same effect may occur in the environmental radiation monitoring.

Population dose in the vicinity of closed Hungarian uranium mine

In order to determine the exposure to natural sources of radiation for people in the vicinity of remediated Hungarian uranium mine regional surveys were carried out. The surveys evaluated indoor radon concentrations and outdoor and indoor external gamma dose rates. Radon concentration has been measured with nuclear etched track detectors for 4 months in 129 houses in Kovágószolos and in 23 houses in Cserkút. In some houses measurements have been carried out for a year and the measurement results of the 4 months were corrected according to these. The corrected radon concentrations altered between 15 and 2314 Bq m(-3). An average of 257 Bq m(-3) in Kovágószolos and 125 Bq m(-3) in Cserkút was measured. The average was 434 Bq m(-3) for the 48 houses within 100 m of the passage of the former mine that is under the village of Kovágószolos. The higher values of Kovágószolos are likely to be the result of the influence of mining. The terrestrial gamma-ray dose rate was measured outdoors and indoors at these houses. Values of 139 (62-233) nGy h(-1) and 133 (93-275) nGy h(-1) were measured in Kovágószolos and Cserkút, respectively. The average annual effective doses for the two villages studied were 3 and 5 mSv y(-1), but the maximum value was 40 mSv y(-1).

Terrestrial Gamma Ray Dose Rate Map of the Japanese Islands in Relation to Geological Systems

Terrestrial Gamma Ray Dose Rate Map of the Japanese Islands in Relation to Geological Systems

日本における地表γ線の線量率分布

Nationwide in-situ measurements of terrestrial gamma ray dose rates have been carried out using a scintillation counter. A database of over 4300 entries has been compiled by adding data taken from literature to the data collected by the mentioned survey. A contour map of dose rates in Japan calculated from the database is presented along with a table of dose rates for each bedrock type.

Population dose in the vicinity of old Spanish uranium mines

Regional surveys were conducted to determine exposure to natural sources of radiation for people in the vicinity of old Spanish uranium mines. The surveys evaluated indoor radon concentrations and outdoor and indoor external gamma dose rates. Indoor radon concentrations were measured in 222 dwellings by means of nuclear track-etched detectors. The terrestrial gamma ray dose rate was measured outdoors and indoors at a total of 256 points and 115 points, respectively. Estimates mean annual effective doses for the six areas studied ranged from 3.2 to 5.1 mSv per year, which is between 1.2 and 2 times higher than the average national value.

Population dose in the vicinity of old Spanish uranium mines

Regional surveys were conducted to determine exposure to natural sources of radiation for people in the vicinity of old Spanish uranium mines. The surveys evaluated indoor radon concentrations and outdoor and indoor external gamma dose rates. Indoor radon concentrations were measured in 222 dwellings by means of nuclear track-etched detectors. The terrestrial gamma ray dose rate was measured outdoors and indoors at a total of 256 points and 115 points, respectively. Estimates mean annual effective doses for the six areas studied ranged from 3.2 to 5.1 mSv per year, which is between 1.2 and 2 times higher than the average national value.

A Survey of Terrestrial Gamma Ray Dose Rates of Nara Prefecture

A Survey of Terrestrial Gamma Ray Dose Rates of Nara Prefecture

Simple soil mass balance approach to interpret the distribution of global terrestrial gamma ray dose rates in relation to geology

A recent literature survey on natural gamma rays has yielded data on the dose rate levels above soils and rocks in the world, classified by their associated bedrock types. For comparison, the data in the Japanese Islands were also collected. The compiled results indicated a strong linear correlation between the soil and the rock dose rates. A soil–mass balance model was used to obtain the quantitative estimate of soil production and inflow rates, respectively, relative to the outflow rate. It was found from the analysis that the degree of mixing of soils, measured by the ratio between the inflow and the production rates, was fairly small in Japan compared to the world average.

地表γ線線量率分布の揺らぎに関する二次元パワースペクトルの推定

世界各地から集めた自然環境における地表γ線線量率データ50組を多変量解析した。データの分散を平均値および測定場所の面積の関数として経験式にまとめた。本研究でとりあげたデータの範囲は, 平均値が10から100 (nGy/h) , 面積が10-3から107 (km2) にわたる。分散の経験式から等方変動場に対する二次元パワースペクトルの式を理論的に導いた。すなわち, S (k) =0.952×10-3m2.02k-2.36である。ここでk (cycles/km) およびm (nGy/h) はそれぞれ波数および平均値である。以下の二つの方法で得たパワースペクトルと比較することにより本研究で推定した二次元パワースペクトルの妥当性を確認した。一つは, 地表面サーベイによるデータ数170以上の二次元ランダム配置データ数組の空間的自己相関解析である。もう一つは航空機サーベイで作られた線量率地図から採取した二組の100×100行列データの直接二次元フーリエ変換である。

Level of natural and artificial radioactivity in Algeria

A national environmental sampling program was carried out during 1993 to determine natural and artificial radionuclides contents in the (0–15 cm) upper layer of the soil. The main objective was to establish a radioactive reference level in the whole territory, since 131I, 134Cs and 137Cs were detected in most of the analysed samples collected right after the Chernobyl accident (May 1986). Soil samples were analysed by direct counting by gamma-ray spectrometry. In addition, terrestrial gamma-ray dose rates in air have been measured out of doors throughout Algeria. In each of the 48 administrative divisions of the country selected sites were chosen to collect soil samples and measure gamma-ray dose rates. The gamma-emitting radionuclides resulting from the radioactive decay of 238U and 232Th, 40K and 137Cs were detected in most of the analysed samples. Radioactivity concentrations in Bq kg −1 dry mass in soil samples of 226Ra, 214Pb, 214Bi, 212Pb, 228Ac, 40K and 137Cs range between (5–176), (2–107), (3–65), (2–97), (3–144), (36–1405) and (0.3–41) respectively. In addition, six selected soil samples were analysed to determine plutonium isotopes contents. Radioactivity concentrations in Bq kg −1 dry mass of 238Pu and 239 + 240Pu vary between (0.012–0.013) and (0.24–0.61) respectively. The dose rates in air measured over the whole country were found to range between 20 and 133 nGy h −1. Presence of 137Cs has been clearly observed. An approach has been made to determine its origin, considering the global fallout, the Chernobyl accident and the French nuclear bomb tests in the 60s as the main potential sources. It is concluded that Algeria has indeed been affected by the Chernobyl accident.

The Structure of Spatial Fluctuation in Terrestrial Gamma-Ray Dose Rate Levels Observed through One-Dimensional Surveys.

Statistical analyses were performed for 50 sets of equal interval data of natural terrestrial gamma-ray dose rates observed for various distances. The multiple regression analysis shows that the variance of a set of data can be expressed as a function of the length and the mean value of the data with relatively high correlation coefficient. One-dimensional spectral analyses for the 50 sets of data suggest that the structures of fluctuation are similar to one another for various distances of observation starting from 0.1 km to about 7 000 km. Each power spectral density can be approximated in the form of P (k) =0.780×10-3 m2.20 k-1.18 where k (cycle/km) and m (nGy/h) are the wave number and the mean, respectively.

One Dimensional Spectral Analysis of Spatial Variations in Terrestrial Gamma-Ray Dose Rate.

Space series analysis was made for 12 sets of equal interval data of terrestrial gammaray dose rate collected in the Japanese Islands, North America and Iceland. Each power spectral density (PSD) could be approximated in the form of P (k) =a·k-n, where P and k were the PSD and wave number, respectively, and a and n were a constant. The value of n ranged from around 1 to 1.7 and the average amounted to 1.3 for a wave-number region of 10-4 -103 cycles/km. The PSDs were divided into two groups having an average of a of 0.1 for Iceland data and that of 5.6 (nGy/h) 2⋅km for others.

Terrestrial gamma radiation levels outdoors in Cantabria, Spain

Terrestrial gamma-ray dose rates have been measured outdoors throughout the region of Cantabria, located in the north of Spain. Results obtained are shown in tabular and cartographical form and are related to the nature of the ground and other influencing factors. The mean absorbed dose rate in air outdoors is 35.46 nGy h-1. The mean annual effective dose equivalent, when the duration of outdoor exposure and distribution of the population are considered, is about 32 mu Sv. This dose is in addition to those doses received from other sources of natural radiation, principally from the presence of radon gas indoors.

A Geochemical Assessment of Terrestrial Gamma-ray Absorbed Dose Rates

A survey of the geochemical literature and unpublished data has resulted in the classification of the concentrations of the naturally occurring radioelements U, Th, and K by their associated rock types. A data base of over 2500 entries has been compiled, permitting calculation of terrestrial gamma-ray absorbed dose rates. The general lithology of terrains may be distinguished by their radioelement ratios, relative abundances, and total gamma radioactivities. The gamma-ray absorbed dose rates in air above igneous rocks generally vary with their silica contents, and with the exception of shale, sedimentary rocks have lower K:U and K:Th ratios than most igneous rocks. The appreciable difference between the overall mean terrestrial gamma-ray dose rate for rock of the continental surface (approximately 7 X 10(-8) Gy h-1) and the mean dose rate from field measurements over soil (approximately 5 X 10(-8) Gy h-1) is explained by the substantial differences between radioelement concentrations of soil and rock, differences that may vary markedly with rock type.

Natural and fallout radioactivity in the San Francisco Bay area.

A compilation of gamma spectrometric data from soil samples collected at 27 fallout monitoring locations in the San Francisco Bay area reveals that natural terrestrial gamma-ray dose rates range from 3–13 μr/hr with a modal value of 5.5 μR/hr (a 10-yr background dose of 480 mr). There is good agreement between the natural dose rates determined by radioactivity measurements made in the field with a portable counter and those derived in the laboratory by pulse-height analyses of soil samples. Analysis of the measurements made with the portable NaI counter from March 1958 through March 1968 yields an average fallout gamma-ray integrated dose for the 27 locations of 280 mr, assuming that all fallout was deposited evenly with respect to time. Roughly three times as much gamma-emitting fallout was deposited in the San Francisco Bay area between March 1958 and the end of 1960 as has been deposited since 1960.