Worldwide Average Values Research Articles

A preliminary report on the determination of natural radioactivity levels of the State of Qatar using high-resolution gamma-ray spectrometry

This study is aimed at the determination of the activity concentrations of naturally occuring and technically enhanced levels of radiation in soil samples collected across the landscape of Qatar. Representative soil samples from various locations across the Qatarian peninsula have been collected and analyzed in order to establish activity concentrations associated with the 235,8U and 232Th natural decay chains and also the long-lived naturally occurring radionuclide 40K. The activity concentrations have been measured using a hyper-pure germanium detector. Details of the sample preparation and the gamma-ray spectroscopic analysis techniques are presented, together with the preliminary values of the activity concentrations associated with the naturally occuring radionuclide chains for six soil samples collected from the Qatarian peninsula. Sample 228, which has been collected from an inshore oil-field area, was observed to have the highest observed value of 226Ra concentration among the six samples. The weighted mean values of the activity concentrations of the radionuclides 238U, 232Th and 40K in one particular sample (sample 228) were, respectively, found to be 213.9±1.4, 4.55±0.11 and 111.4±3.6 Bq/kg, which compare with the worldwide weighted mean values in soil samples, 33, 45 and 420 Bq/kg, respectively. The deduced activity concentration of 238U in sample 228 in the current work was found to be significantly higher than the worldwide average value and was also significantly higher than the values determined for the five other initial samples discussed here. The mean values of the activity concentration of the 232Th series, 40K and 137Cs in Bq/kg from the six investigated soil samples were found to be 9.4±1.3, 204±22 and 5.8±5.6, respectively, with the quoted uncertainty referring to the standard deviation among these measurements.

External dose-rates for natural gamma emitters in soils from an agricultural land in West Anatolia

The surveys of natural gamma-emitting radionuclides in soils from three basins of West Anatolia intensively used for agricultural purposes were conducted during 1998–2003. In the present study, part of the survey, the activity concentrations of 238U, 232Th and 40K in the soil samples from 43 sites distributed all over the agricultural land known as Buyuk Menderes basin were determined by scintillation gamma spectrometry. The average activity concentrations and ranges of the relevant radionuclides in the soils were as follows: 238U was 29 (7–84); 232Th, 22 (10–48) and 40K, 464 (100–864) Bq kg−1. The corresponding absorbed dose rates in air from all those radionuclides were in the range of 17–81 nGy h−1 with a mean value of 46 nGy h−1 and did not exceed the world-wide average values. All dosimetric calculations were performed based on the guidance of UNSCEAR 2000 report [1].

210-Polonium studies in some environmental and biological matrices of Domiasiat uranium deposit area, West Khasi Hills, Meghalaya, India

The study was performed using a silicon surface barrier alpha spectrometer at Bhabha Atomic Research Centre, Mumbai, India. Through the study, the observed (210)Po activity in water sample from different locations in the Domiasiat area ranges from 0.04 to 0.69 Bq/l. The daily and annual intake of (210)Po through water was also estimated and the mean value of 0.72 and 263.61 Bq, respectively, were observed. It is observed that the effective doses through water were higher than the World Health Organization recommended dose of 0.05 mSv/year. The total annual effective doses through terrestrial ingestion for all the locations was studied and the mean annual effective dose was observed to be 0.315 mSv, which, when compared to the worldwide and the Indian values, was observed to be slightly higher. The mean activity in soil is found to be 124.8 +/-5.7 Bq/kg and in meat the activity is 0.43 +/-0.05 Bq/kg. In fishes, an activity of 0.48 +/-0.07 Bq/kg in Garra lamta, 0.29 +/-0.02 Bq/kg in Neolissocheilus hexaganolepis, and 3.3 +/-0.1 Bq/kg in Macrobrachium sp. is observed. Activity concentration in plant samples was analyzed and the activity ranges from 0.020 +/-0.002 to 9.69 +/-0.35 Bq/kg. Committed effective dose by the adult population of the Domiasiat area through intake of (210)Po through these food items was also determined and compared with the Indian average value and the worldwide average value.

CONCENTRATIONS OF 226Ra, 232Th, AND 40K IN THE SOILS OF BANGALORE REGION, INDIA

Several soil samples of Bangalore region were analyzed for the concentrations of Ra, Th, and K by gamma ray spectrometry. The concentration of Ra varied in the range 7.7-111.6 Bq kg with a mean value of 26.2 Bq kg, Th in the range 16.7-98.7 Bq kg with a mean of 53.1 Bq kg, and that of K in the range 151.8-1424.2 Bq kg with a mean of 635.1 Bq kg. The external gamma absorbed dose rates in air were also measured using a portable environmental radiation dosimeter, and the gamma dose rates were found to vary in the range 61.4-201.7 nGy h with a mean of 117.2 nGy h. These results along with the results of estimation of radium equivalent activity (Raeq), absorbed dose rate (D), annual effective dose rate, external hazard index (Hex), internal hazard index (Hin), and representative level index (Igamma) are presented in this paper. The results are also compared with the literature values reported for other regions of India as well as worldwide average values and discussed.

Population doses from terrestrial gamma exposure in Serbia

Background: Terrestrial radiation emitted from naturally occurring radionuclides, such as 40K and radionuclides from the 238U and 232Th series and their decay products represent the main external source of irradiation to the human body. The purpose of this study was to provide a preliminary assessment of the doses from terrestrial exposure of population in Serbia and to estimate a potential radiation hazard for population inhabiting investigated areas. Methods: The gamma dose rates, external hazard indexes, and annual effective doses due to terrestrial naturally occurring radionuclides (238U, 232Th and 40K) were calculated based on their activities in soil samples in Serbia as determined by gamma-ray spectrometry. Results: The total absorbed gamma dose rate due to these radionuclides varied from 16.9 to 125 nGy h-1, with a mean of 62.8 nGy h-1. Assuming a 20% occupancy factor, the corresponding annual effective dose varied from 2.07 to 15.4?10-5 Sv with the mean value of 7.7?10-5 Sv, i.e. annual effective dose was in range of the world wide average values. Conclusion: According to the values of external hazard index obtained in this study (mean Hex = 0.35), the radiation hazard was insignificant for the population living in investigated areas.

Assessment of occupational exposure to uranium by indirect methods needs information on natural background variations

Urine monitoring is the preferred method to determine exposure to soluble compounds of uranium in workplaces. The interpretation of uranium contents in workers bioassay samples requires knowledge on uranium excretion and its dependence on intake by diet. Exceptionally high concentrations of natural uranium in private drinking water sources have been measured in the granite areas of Southern Finland. Consequently, high concentrations of natural uranium have been observed in the urine and hair samples of people using water from their own drilled wells. Natural uranium content in urine and hair samples of family members, who use uranium-rich household water, have been analyzed by using ICP-MS. The uranium concentrations both in urine and hair samples of the study subjects were significantly higher than the world-wide average values. In addition, gammaspectrometric methods have been tested for determining uranium in hair samples. This method can be used only for samples with highly elevated uranium concentrations.

Assessment of gamma dose rates from terrestrial exposure in Serbia and Montenegro

The gamma dose rates due to naturally occuring terrestrial radionuclides ((226)Ra, (232)Th and (40)K) were calculated based on their activities in soil samples, determined by gamma-ray spectrometry. A total of 140 soil samples from 21 different regions of Serbia and Montenegro were collected. The gamma dose rates ranged from 7.40 to 29.7 nGy h(-1) for (226)Ra, from 12.9 to 46.5 nGy h(-1) for (232)Th and from 12.5 to 37.1 nGy h(-1) for (40)K. The total absorbed gamma dose rate due to these radionuclides varied from 34.5 to 97.6 nGy h(-1) with mean of 66.8 nGy h(-1). Assuming a 20% occupancy factor, the corresponding annual effective dose varied from 4.23 x 10(-5) to 11.9 x 10(-5) Sv with mean of 8.19 x 10(-5) Sv, i.e. the dose was lower than world wide average value. According to the values of external hazard index (mean: 0.39) obtained in this study, the radiation hazard was found to be insignificant for population living in the investigated area.

Levels of Lanthanides and Natural Radionuclides in the Uncultivated Soils Near Industrial Area of Bangladesh

Twenty-five uncultivated surface soil samples collected from the northern and southern regions of Dhaka Export Processing Zone (DEPZ), industrial area of Bangladesh, were analyzed for their contents of Y, lanthanides and natural radionuclides (Th and U) using an inductively coupled plasma mass spectrometer (ICP-MS). Analogous concentrations of the Y, lanthanides, Th and U were observed in the both regions of DEPZ around several kilometer distances. Further, the measured values showed no particular contamination. However, the concentrations of the light lanthanides (La, Ce and Nd) in the Bangladeshi soils were around twice the worldwide average value. But, the smooth curve of the chondrite normalized patterns of the lanthanides suggested that the lanthanide contents of the Bangladeshi soils in this area are the results of the natural dispersion process rather than anthropogenic activities. In addition, the relatively high Th and U concentrations and Th/U ratio were observed in Bangladeshi soils of this area, most likely due to the effect of their parent materials such as clay stones which have a high Th/U ratio. Since this is the first precise result for the Y, lanthanides, Th and U contents in Bangladeshi soils, it could be useful in understanding the background level and the characteristics of these elements in Bangladeshi soils.

Attenuation and source parameters at Deception Island (South Shetland Islands, Antarctica)

Deception Island is the most active volcano of the South Shetland Islands-Antarctic Peninsula group, experiencing eruptions in 1967, 1969 and 1970. Local attenuation derived from coda analysis and source parameters derived from Brune's model, for well located seismic events, have been studied in order to complement the available geophysical information. Results show abnormally lowQ0 values and an abnormally high frequency dependence, as well as large dispersion. These factors are strongly dependent on the path travelled by the seismic wave. Retrieved values of the source parameters (stress drop, seismic moment and source radius), are again abnormally low compared to world-wide average values, for example, those obtained for the Oroville, California aftershock series between June and September, 1976. These results are consistent with some aspects of the geology of Deception Island, such as the very high degree of fracturing and faulting, and the existence of a strong hydrothermal alteration affecting most of the subaerial volcanic rocks. Moreover, the pattern defined for the lateral variations ofQ0 shows minimum values in the inner bay of the island, close to the most recent eruption vents. A large reduction in spectral amplitudes over a particular frequency range occurs in several observations, corresponding to the path crossing the zone of highest attenuation. This observation suggests the existence of a hot magmatic intrusion produced during the most recent eruption, and coincides with the superficial low density mass distribution obtained from the gravimetric model and the long wave magnetic field component obtained from magnetic surveys. The width of this intrusion is estimated to be about 200 m, in agreement with the previous results obtained analyzing residuals of the location of seismic events.

Frequency distribution and quantification of deep earthquakes

The frequency distribution of deep earthquakes (d > 350 km) is analyzed on a regional scale, using magnitude data from ∼4660 events reported in the International Seismological Center Bulletin (1964–1982) and 391 centroid moment tensor solutions (1977–1987). We use the moment magnitude Mw to define b values comparable with studies of shallow seismicity; scaling laws relating Mw, mb, and Mo are derived (Mw = 1.6mb − 3.2; mb = [log Mo − 4.3]/2.4) which compare very favorably with published laws. Uncertainties and biases of the mb and Mo data sets are considered. The slope of the frequency distribution is evaluated over a restricted magnitude range; the results are very robust and independent from the magnitude range used. From the mb magnitude data we obtain regional b values in the range 0.4 < b < 1.22, with a worldwide average value b = 0.87; these results are confirmed by the analysis of the seismic moment data. The steepest frequency distribution is observed in the Tonga Islands region (b = 1.22); although ∼60% of the worldwide deep seismicity occurs here, only few events since 1977 had seismic moment exceeding 1019 N m. The high fractal dimension (D = 2.4) implies a volume partially filled with fault planes, in agreement with the observations on the seismic morphology of the region. At the other extreme. South America is characterized by the largest recorded deep events and an almost complete absence of small ones (b = 0.4).

Rare gas abundances in MORB

Abstract Data are presented for He, Ar and Xe in a number of MORB glasses and crystalline rocks. The rare gases in the latter group are characterized by atmospheric Ar and Xe, coupled with loss of trapped mantle He, Ar and Xe. The glass data also show clear signs of an atmospheric-like component for Ar and Xe. A reasonably constant world-wide average trapped mantle gas value of 40 Ar/ 36 Ar ~15000 ±3000 is suggested. Anomalies are seen in the 129 Xe/ 132 Xe ratio, but at least part of this might be due to mass fractionation rather than to 129 I decay. Correlating the data with those from oceanic island basalts in Ar-Xe space indicates that the latter samples are probably also greatly influenced by an atmospheric component rather than (or in addition to) trapping gases from an undepleted mantle source.

Palaeomagnetic and Rock Magnetic Studies on Cenozoic Basalts from Kyushu, Japan

Summary Some of these Cenozoic basalts are magnetized in either the normal or reversed direction of the axial dipole field but some others are magnetized obliquely. The remanences of the latter are quite as stable as the normal or reversed flows and are interpreted as recording geomagnetic field directions during polarity transitions. When combined with measurements made on rocks from sites some 10 km away from ours, two paths connecting these transitional virtual poles may be traced, one for the lower Pliocene and the other for the upper Pliocene. Both cross central Russia and the Indian Ocean. Palaeosecular variations of the geomagnetic field have been investigated by restricting our studies to flows which yield virtual poles at latitudes higher than 45° and the dispersion of cleaned R.M. directions obtained from such flows agree with world-wide average values. Thermomagnetic, ore microscope and electron microprobe investigations have been made and the shape of the thermomagnetic curves is related to evidence of both low and high temperature oxidation.

THE RELATIONSHIPS BETWEEN THE SECULAR CHANGE AND THE NON-DIPOLE FIELDS

Using airborne, ground, and repeat magnetic observations in Canada compiled in the isomagnetic and isoporic charts for epoch 1955.0, the drift and decay contributions of the non-dipole field to the observed secular variation have been estimated. The drift rates which produce the minimum residual secular variation were found to be unusually small. It is then confirmed, using the longitude displacement method and isomagnetic data only, that the westward drift of the non-dipole field in recent years in Canada is significantly smaller than the world-wide average. These results clearly demonstrate the large local fluctuations which occur in westward drift.The two different methods were applied to obtain relationships between the Gaussian coefficients in the spherical harmonic analyses of the earth's main field and the secular variation. Calculations show that both methods give the accepted world-wide average value of westward drift, that one half of the world-wide secular variation is produced by westward drift, and in general decay terms are unimportant.

The Temperature of the Lower Atmosphere of the Earth

From the known amounts of the various gases of the atmosphere from sea level to about 20 km, from the observed light absorption coefficients of the gases and from the albedo of the earth's surface the temperature of the atmosphere in radiative equilibrium is calculated on the assumption that the sunlight is the only source of energy. The calculation is perhaps more rigorous than has hitherto been attempted, although it contains a number of approximations. The sea level temperature comes out to be about 19\ifmmode^\circ\else\textdegree\fi{} above the observed world-wide average value 287\ifmmode^\circ\else\textdegree\fi{}K, and the temperature above about 3 km falls many degrees below the observed temperatures. The temperature gradient in levels from 3 to 6 km is greater than that of convective equilibrium and hence the atmosphere would not be dynamically stable if radiation equilibrium prevailed. Therefore air currents take place to bring about convective equilibrium. Continuing the calculation it is found that only when the convective region extends to about 12 km (as is observed), with radiative equilibrium above 12 km (as is observed), does the atmosphere satisfy the conditions of dynamic stability and thermal equilibrium with the received solar energy. For this case the calculated sea level temperature is 290\ifmmode^\circ\else\textdegree\fi{}K in good agreement with the observed value 287\ifmmode^\circ\else\textdegree\fi{}K. Calculation shows that doubling or tripling the amount of the carbon dioxide of the atmosphere increases the average sea level temperature by about 4\ifmmode^\circ\else\textdegree\fi{} and 7\ifmmode^\circ\else\textdegree\fi{}K, respectively; halving or reducing to zero the carbon dioxide decreases the temperature by similar amounts. Such changes in temperature are about the same as those which occur when the earth passes from an ice age to a warm age, or vice versa. Thus the calculation indicates that the carbon dioxide theory of the ice ages, originally proposed by Tyndall, is a possible theory.