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1.
The region of Amarante (Northern Portugal) is composed of Hercynian tardi-tectonics granites and Paleozoic metasediments. Petrographic observations and SEM studies show that uranium is mainly contained within the rock in heavy accessory minerals such as apatite, zircon, monazite, uraninite, thorite and thorianite. The geological, geochemical and radiological data obtained suggest that the radon concentrations in dwellings of the studied area are mainly related with the uranium content of the rocks. Indeed, the highest contents were observed in granite AT2 of Padronelo (18.2 ppm) and the granite AT1 of Telões (10.3 ppm), with metasediments showing much lower uranium contents of 1.6 ppm; radon concentrations were evaluated in dwellings, using CR-39 passive detectors, and the results obtained in winter conditions suggest that the most productive geological units are the granites AT2 and AT1, with geometric means of 430 and 220 Bq/m3, respectively, while the metasediments show the lowest value of 85 Bq/m3. Some moderate radiometric anomalies, where uranium contents can double typical background values, were found in relation with specific fault systems of the region affecting granitic rocks, thus increasing radon risk; this is an indication of uranium mobility, likely resulting from the leaching of primary mineral supports as uraninite. Groundwater radionuclide contents show a wide range of results, with the highest activities related with granitic lithologies: 2,295 Bq/l for radon, 0.83 Bq/l for gross α and 0.71 Bq/l for gross β, presenting metasediments much lower values, in good agreement with other results obtained. Absorbed dose measured with gamma spectrometers in direct contact with the rocks is directly related with the uranium contents of the rocks, and thus works as a fast proxy for radon risk. It is concluded that radon risk is moderate to high in the granitic areas of the Amarante region and low in the metasediments of the same region.  相似文献   

2.
Indoor radon measurements were carried out in a total of 420 dwellings and 17 schools in Hail region of Saudi Arabia, using NTDs based radon dosimeters. The duration of the measurements was one year, from April 2008 to April 2009. The indoor radon concentrations varied from 4 to 513 Bq/m3 with an overall average of 45 Bq/m3 for all surveyed dwellings. These passive measurements were confirmed by the active measurements. The anomalous concentrations above 200 Bq/m3 were observed in 13 dwellings, representing 3.1 % of the total surveyed dwellings. In Inbowan village alone, it was found that 7.6 % of the dwellings have indoor radon concentration above 200 Bq/m3. The highest average indoor radon concentration of 64 Bq/m3 was found in Inbowan village while the lowest average of 24 Bq/m3 was found in Majasah village. The city of Hail showed an average indoor radon concentration of 49 Bq/m3. The average indoor radon concentration in one area located at the edge of the Aja Mountain in Hail city was 111 Bq/m3. The elevated indoor radon concentrations in many dwellings in the Hail region, prompted us to measure outdoor ground radon in such locations using gas monitor. It was found that radon concentrations at a depth of 0.5 m varied significantly from place to place ranging from 1.2 to 177 kBq/m3. The outdoor radon concentrations are generally correlated with the indoor radon measurements. Radon exhalations from construction materials and soil samples from the Hail region were also measured. It was found that radon exhalations from soil samples are higher than that of construction materials by a factor of at least 3 and reaching up to 11. These results indicate that soil is the main source of indoor radon. Geological interpretations of the results are also given.  相似文献   

3.
A study of the indoor radon gas levels was performed in 935 homes in Scania, southernmost Sweden, located on geologically different ground with regard to uranium (U) content. In one of these two areas the bedrock consists of alum shale with U contents exceeding 200 ppm. In the other area there is no U-rich bedrock. Indoor radon levels are influenced by U content and permeability as shown below.For maam nancy for table, please place here. Thanx!The results show that the indoor radon levels were highest in homes located on bedrock with medium to high U content combined with a highly permeable drift covering the bedrock. The difference was statistically significant(P < 0.0001). Other results of the investigation are: 14 homes built from aerated concrete made from U-rich alum shale had higher levels than 767 homes with walls from other material (312 vs 106 Bq/m3;P = 0.0011); 242 homes with a cellar had lower radon levels than 563 without (62 vs 138 Bq/m3;P <0.0001); further, 418 homes with private well had higher levels than 360 with public water supply (140 vs 82 Bq/m3;P <0.0001). The results of the investigation show a profound effect of a combination of high bedrock U content and high cover permeability. The effect of the uraniferous drift on the indoor radon levels is evident. Thus, the geological conditions should be carefully considered when screening for high-risk buildings, as well as when planning for new ones. Also, the construction of the building and its water supply have some influence.  相似文献   

4.
Radon measurements in soil and groundwater (springs, thermal springs and handpumps) were made in a variety of lithological units including major thrusts between Mandi and Manali in Himachal Himalaya. Analysis of radon data in light of lithological controls and influence of deep-seated thrusts has been made to elucidate the causative factors for anomalous emanation of radon. The lithological types include banded gneisses, schists, quartzite, granite, phyllites, volcanics and mylonites. The low-grade metasedimentries of Shali and Dharamsala generally show low and narrow range of radon concentration in water (5.6–13.4 Bq/l) as well as in soil (1.8–3.2 kBq/m3) except for the samples related to thrusts. On the other hand, sheared and deformed rocks of Chail and Jutogh show moderate radon content (average 5.03 kBq/m3, range 2.9–11.1 kBq/m3) in soil. However, the groundwater radon concentration shows wide variation in different types of sources (2.1–80.8 Bq/l). The quartzite and volcanic rocks of Rampur formation in this area present as a window separated by Chail thrust. Radon emanations on these rock types are relatively high (6.3–68.1 Bq/l in water and 5.5–15.9 kBq/m3 in soil) and are exceptionally high in samples that are related to uranium mineralization, deep-seated thrusts and hot springs (13.5–653.5 Bq/l). It is generally observed that anomalous high radon content is associated with mineralization, deeper source and tectonic discontinuities. Whereas it is obvious that subsurface radioactive mineralization would facilitate enhanced radon production, however, thrust plains provide easy pathways for escape of gases from the deeper sources. Shallow and deep sources of the groundwater have contrasting radon content particularly in the deformed and metamorphosed rocks of Jutogh and Chail. Shallow groundwater sources, mainly handpumps, have lower radon concentration due to limited superficial water circulation, whereas deeper sources, mainly perennial springs, show higher radon content because of larger opportunity for water–rock interaction.  相似文献   

5.
The Miao'ershan uranium ore district is one of the most important granite-hosted uranium producers in South China. There are several Triassic granite plutons in the Miao'ershan batholith, but uranium ore deposits mainly occur within the Douzhashan granitic body. Precise zircon U–Pb dating indicated that these Triassic granite plutons were emplaced during 204 to 215 Ma. The Douzhashan U-bearing granite lies in the central part of the Miao'ershan batholith, and has higher U contents (8.0 to 26.1 ppm, average 17.0 ppm) than the nearby Xiangcaoping granite (5.0 to 9.3 ppm, average 7.0 ppm) and the Yangqiaoling granite (6.4 to 18.3 ppm, average 11.5 ppm) in the south part of the batholith. The Douzhashan granite is composed of medium-grained two-mica granite, whereas the Xiangcaoping and Yangqiaoling granites are composed of porphyritic biotite granite. Both the Xiangcaoping and Douzhashan granites have high A/CNK ratios (> 1.10), high (87Sr/86Sr)i ratios (> 0.720) and low εNd(t) values (− 11.3 to − 10.4), suggesting that they belong to strongly peraluminous S-type granites. The Douzhashan granite has low CaO/Na2O ratios, high Rb/Sr and Rb/Ba ratios, indicating a partial melting origin of clay-rich pelitic rocks. In contrast, the Xiangcaoping granite formed from clay-poor psammite-derived melt. The Yangqiaoling granite shows different geochemical characteristics with the Douzhashan and Xiangcaoping granites, indicating a different magma source. The Yangqiaoling granite has higher εNd(t) of − 9.4 to − 8.3 and variable A/CNK values from 0.98 to 1.19, suggesting a mixture source of meta-sedimentary rocks and meta-igneous rocks. Crystallization fractionation is not the main mechanism for U enrichment in the Douzhashan granite. We suggest that U-rich pelitic rock sources may be the key factor to generate peraluminous U-bearing granites in South China. Searching for those granites which are reduced, strongly peraluminous and were derived from U-rich pelitic rocks, is the most effective way for exploring granite-hosted U deposits.  相似文献   

6.
 Radon concentrations were measured in soil, air and groundwater in Bhilangana Valley, Garhwal Himalaya, India by using an LR-115 plastic track detector and radon emanometer. Radon concentrations were found to vary from 1 KBq/m3 to 57 KBq/m3 in soil , 5 Bq/l to 887 Bq/l in water and 95 Bq/m3 to 208 Bq/m3 in air. The recorded values are quite high due to associated uranium mineralization in the area. Radon concentration was also found to depend on the tectonic structure and geology of the area. Received: 22 July 1996 · Accepted: 8 January 1997  相似文献   

7.
The Zhuguangshan complex carries some of the most important granite-hosted uranium deposits in South China. Here we investigate the Changjiang and Jiufeng granites which represent typical U-bearing and barren granites in the complex, using zircon U-Pb ages, whole-rock geochemistry, Sr-Nd isotopic and zircon Hf isotopic data, and mineral chemistry, to constrain the petrogenesis and uranium mineralization. LA-ICP-MS zircon U-Pb dating shows that both the Changjiang and Jiufeng granites were emplaced ca. 160 Ma. These rocks show high silica, weakly to strongly peraluminous compositions, enrichment in Rb, Th, and U, and depletion in Ba, Nb, Sr, P, and Ti. These features coupled with the high initial 87Sr/86Sr ratios, negative εNd(t) values and εHf(t) values, and the Paleoproterozoic two stage model ages of these two granites suggest that the two granites belong to S-type granites, and the parental magmas of the two granites were derived from the Paleoproterozoic metasedimentary rocks. However, the granitoids show different mineralogical characteristics. The biotite in the Changjiang granite belongs to siderophyllite, marking higher degree of chloritization, whereas the biotite in the Jiufeng granite is ferribiotite, characterized by only slight chloritization. Compared with the Jiufeng granite, the biotite in the Changjiang granite has lower crystallization temperature and oxygen fugacity, but higher F content, and the uraninite has higher UO2 content but lower ThO2 content, and stronger corrosion. The chemical ages of uraninites from both granites are (within error) consistent with the zircon U-Pb ages and are considered to represent the emplacement ages of granites. Chemical ages of pitchblende in the Changjiang granite yield 118 ± 8 Ma, 87 ± 4 Ma, and 68 ± 6 Ma, representing multiple episodes of hydrothermal events that are responsible for the precipitation of U ores in the Changjiang uranium ore field. Our study suggests that the degree of magma differentiation and physicochemical conditions of the magmatic-hydrothermal system are the key factors that control the different U contents of these two granites. The mineralogical characteristics of uraninite and biotite can be used to distinguish between U-bearing and barren granites, and serve as a potential tool for prospecting granite-hosted uranium deposits.  相似文献   

8.
It has been established that radon and its airborne decay products can present serious radiation hazards. A long term exposure to high concentration of radon causes lung cancer. Besides, it is also known that out of the total radiation dose received from natural and man-made sources, 60% of the dose is due to radon and its progeny. Taking this into account, an attempt has been made to estimate radon concentration in dwellings in and around Guwahati using aluminium dosimeter cups with CR-39 plastic detectors. Results of preliminary investigation presented in this paper show that the mean concentration is 21.31 Bq m − 3.  相似文献   

9.
In SW Sardinia syngenetic to syndiagenetic Pb-Zn ores occur in Cambrian carbonates, along the unconformity between the Cambrian and Ordovician, in Permo-Triassic karsts and in vein-type deposits related to late Hercynian granites, which also contact-metamorphosed some Cambrian deposits. In all types of deposits the leadisotope ratios show similarly high (=238U/204Pb) and high W (=232Th/204Pb) values indicating a crustal origin for the lead. Most of the Cambrian ores contain isotopically similar or identical leads, whereas in the younger deposits the isotope ratios vary and suggest that especially the lead of Permo-Triassic ores may consist to a large extent of remobilized Cambrian, possibly also Ordovician, ore lead plus a Hercynian component.The lead of three feldspar samples from Hercynian granites of the area also shows high and W values. Two of them are similar to the ore leads from a vein-type deposit and from contact-metamorphosed deposits. The third sample from the Capo Pecora granite contains a very unradiogenic lead that closely resembles many of the presumed Cambrian-Hercynian mixtures. Therefore, the possibility cannot be dismissed that at the time the Permo-Triassic ores were formed lead sources other than the already existing ores were present with the appropriate isotopic compositions.  相似文献   

10.
An attempt was made in the present study to delineate how the radon concentrations vary with respect to different geological formations and to evaluate annual effective dose exposure due to ingestion of radon. A total of 60 groundwater samples were collected from layered sequential aquifers in Chitradurga district having major rock types such as Bababudan Group, Charnockite, Chitradurga Group, Closepet granite, migmatites and granodiorite — tonalitic gneisses and Sargur Schist complex during pre-monsoon and post-season of the year 2011. Radon measurement was made using Durridge RAD-7 radon-in-air monitor, connected to RAD H2O accessory with closed loop aeration concept. In the present study, the radon activity ranged from 0 to 186.6 Bq/L and 0 to 150.6 Bq/L during pre- and post-monsoon seasons of the year 2011, with 56.67 % (17 samples) of samples during both the seasons exceeding the EPA’s MCL value of 11.1 Bq/L. The annual mean radon activity in the groundwater was higher in the area having Chitradurga rock group formations (78.1 Bq/L) followed by Sargur-Satyamangalam schist complex group (56.8 bq/L), migmatites and granodiorite — tonalitic Gneisses group (56.3 Bq/L), Closepet granite (42.7 Bq/L), Charnonkite (29.1 Bq/L) and Bababudan Group (22.2 Bq/L). It is inferred that radon concentration found to depend on the tectonic structure, geology of the area and on the presence of uranium minerals in these rocks. The annual effective dose resulting from radon in groundwater in the Chitradurga district were significantly lower than UNSCEAR and WHO recommended limit of 1 mSv/y.  相似文献   

11.
A radon risk map for the Walloon region of Belgium, based on the two databases available, has been calculated and is presented in this work. The data are organized into geological units. For each unit, an average logarithmic standard deviation is calculated, after correcting the higher variability of short term data. The region is divided with an 1-km grid. For each node, the local geological unit is determined, as well as the corresponding logarithmic standard deviation. The logarithmic mean is evaluated by smoothing the data belonging to the same geological unit as the node. Assuming a log-normal distribution, a map that shows for each node the predicted percentage of buildings with an indoor radon concentration above the Action level (400 Bq/m3) is constructed. This is the first radon risk map for this region that fully takes into account the geological information.  相似文献   

12.
为查明二连盆地苏尼特右旗地区HFU-39、HFU-40航放异常的铀成矿情况,本文在分析异常区区域地质资料基础上,采用地质剖面测量、地面伽玛总量测量、伽玛能谱剖面测量、土壤氡剖面测量及岩石化探取样分析综合方法,对HFU-39、HFU-40两个异常进行查证及评价。查证结果显示异常呈团块状展布,地面伽玛能谱测量铀含量最高达w（U）=135×10-6,岩石化学分析铀含量最高达w（U）=256×10-6,该区域氡异常突出;综合异常查证结果和对二连盆地泥岩型铀矿化的形成环境分析,指出了该区的下一步铀找矿方向。  相似文献   

13.
The potential genetic link between granites and their host sediments can be assessed using zircon age inheritance patterns. In the Lachlan fold belt, southeastern Australia, granites and associated high-grade metasedimentary rocks intrude low-grade Ordovician country rock. This relationship is well-exposed in the Tallangatta region, northeast Victoria (part of the Wagga-Omeo Metamorphic Complex). In this region granites (two I-types and two S-types) have intruded during the mid-late Silurian between approximately 410–430 Ma based on the ages of magmatic zircons. The age spectra for inherited zircons from the granites have been compared with those of detrital zircons from the enclosing low- and high-grade metasediments. In broad terms, both for detrital zircons in all four sediments and for inherited zircons in three of the four granites, the dominant ages are early Paleozoic and Late Precambrian, with sporadic older Precambrian ages extending up to 3.5 Ga. The ages of the youngest detrital zircons from the low-grade Lockhart and Talgarno terranes limit the time of sedimentation to ca. 466 Ma or younger. The youngest detrital zircons from two samples of the high-grade Gundowring terrane are 473 Ma, making these sediments Ordovician or younger, not Cambrian as originally suggested. However, the individual age spectra for the four selected metasediments are not well matched when closely examined. The age spectra of the inherited zircons in the granites also do not adequately match those in any of the metasediments. Thus, the metasediments might not be representative of the actual source rocks of the granites. While the exact source of the granites cannot be identified from the analysed samples, the existence of a large population of ca. 495 Ma inherited zircon grains in the S-type granites requires that the granite source contains a significant proportion of Cambrian or younger material. This does not preclude the existence of a Precambrian basement to the Lachlan fold belt but indicates that at the level of S-type magma generation, a Cambrian and/or younger protolith is required. Received: 28 August 1998 / Accepted: 7 July 1999  相似文献   

14.
Mineralogical, fluid inclusion and geochemical studies were made on two intra-granitic gold deposits (Grovelas and Penedono), together with a deposit linked to sub-vertical structures in silicified metasediments at Três-Minas, and several intra-metamorphic occurrences at Vila Pouca de Aguiar. They all possess similar mineral assemblages, deformational state, fluid flow characteristics, ore fluid composition and have comparable P–T conditions. Three successive crystallisation stages are recorded during the formation of gold-bearing structures independent of their location or host rocks (granites or metasediments). They are:Stage 1 — the development of milky quartz veins that formed primarily after the emplacement of peraluminous two-mica granites (315–310 Ma) at P–T conditions reflecting high temperature and low pressure. They are similar to those from pluton induced metamorphism (P=300–350 MPa and T=500–550°C). No clear evidence was found for gold deposition during this stage.Stage 2 — during orogenic uplift and repeated tectonic reactivation a clear quartz was deposited in the early milky quartz veins (Stage 1) at P–T conditions between 100 and 300 MPa and 300 and 450°C. Local sulphide deposition (arsenopyrite II and pyrite II) occurred in clear quartz, but was never massive. The fluids percolating within the granite were mainly aqueous-carbonic and reflect equilibrium with the metamorphic host rocks. They are very similar to those found in metamorphic environments. No evidence for the involvement of magmatic fluids was found.Stage 3 — intense microfissuring of the earlier vein infillings occurred, associated with the main episode of gold deposition. The P–T conditions were <100 MPa and <300°C based on aqueous fluid inclusions. Native gold and electrum crystallised together with sulphides (galena, chalcopyrite and bismuthinite), native Bi and sulphosalts (Pb–Bi–Ag dominated). The fractures frequently contain chlorite (± sericite) especially where they crosscut earlier sulphides (arsenopyrite).These processes and fluid types are similar in both the granites and metamorphic host rocks. Therefore, the gold ores appear to be the result of successive periods of fluid circulation, in this case related to the uplift of the Variscan basement in response to high heat flow and the intrusion of granites. Without exception, these fluids have been re-equilibrated with the metamorphic rocks. However magmatic fluids are absent; the granites thus act passively as heat engines for fluid circulation.  相似文献   

15.
Soil-gas radon measurements provide a valuable tool in assessing probable indoor radon levels on a regional basis. However, in Great Britain, seasonal weather changes can cause large changes in soil-gas radon concentration. Although this does not significantly constrain systematic radon potential mapping programmes, it does cause difficulties in responding to ad-hoc requests for site-specific radon investigations. The relationship between soil-gas radon and gamma spectrometry measurements made in the field with radon released from a representative sample of soil in the laboratory has been investigated as part of a program to develop a method of radon potential mapping and site investigation which can be used at any time of the year. Multiple soil and soil-gas samples were collected from sites underlain by bedrocks with widely varying radon potentials. For each geological unit, sites both free of and covered by glacial drift deposits were sampled. Soil and soil-gas samples were taken at the same depth of 60–100 cm. The effectiveness of these radon site investigation procedures has been evaluated by studying the relationship between the soil-gas radon, gamma spectrometry and radon emanation data with an independent estimate of the radon risk. The geologic radon potential (GEORP), which is the proportion of existing dwellings which exceed the UK radon Action Level (200 Bq m−3) for a particular combination of solid and drift geology within a defined geographic area, has been used for this study as the independent estimate of radon risk. Soil-gas radon, radon emanation and eU (equivalent uranium by field γ spectrometry) are all good geochemical indicators of radon risk (GEORP) in Derbyshire but only soil-gas radon correlates significantly with GEORP in Northamptonshire. Radon in soil gas discriminates more effectively between sites with different radon potential in Northamptonshire if soil permeability is also taken into account. In general, measurement of soil-gas radon in the field provides the most universally applicable indicator of radon potential. If soil-gas radon concentrations cannot be determined because of climatic factors, for example when the soil profile is waterlogged, measurement of radon emanation in the laboratory or measurement of eU can be used as radon potential indicators in some geological environments. This applies particularly in areas where the soil composition rather than the composition and permeability of the underlying rock or superficial deposits are the dominant controls of radon potential. It appears, therefore, that it may be necessary to use different radon site investigation methods according to the specific factors controlling radon emanation from the ground. In some cases no method will provide a reliable indicator of radon risk under unfavourable climatic conditions.  相似文献   

16.
Most altered clay minerals in uranium ore deposits in granites in the selected provinces of South China haveδ 18O m values ranging from 6.22 to 7.24,δDm from −60 to −70,δ 18O from +3.05 to −3.07, and from −20.2 to −37.5‰. Relative enrichment of32S in the uranium ore deposits and greater variations in Pb isotopic composition of galenas from them show that uranium ores in the granites were formed in such a way that uranium in shallow-source granites had been mobilized by heated meteoric waters and then migrated to local favourable locations along great faults to form uranium ore deposits. Zhang Shaoli, Yang Wenjin, Tang Chunjing and Xu Wenxin did part of this work.  相似文献   

17.
Radon and its progeny have been recognized as one of the major contributors to the natural radiation and health hazards in the human dwellings. Even lung cancer is expected if it is present in enhanced levels beyond maximum permissible limit. This paper reports the measurements of indoor radon and its progeny in the urban dwellings of the Etah district of Uttar Pradesh province in Northern India using the cellulose nitrate (LR-115 type-II) plastic track detectors. It is found that the values of radon concentration vary from 3.52 to 248.64 Bq m−3 with a standard deviation of 69.19. The values of radon progeny concentration vary from 0.38 to 26.88 mWL with a standard deviation of 7.48. The effective dose has been calculated and found to vary from 0.05 to 3.76 mSv year−1 with a standard deviation of 1.05. The lifetime fatality risk is found to vary from 0.04 × 10−4 to 2.90 × 10−4. The results have been compared with the results reported in the rural areas of the same district.  相似文献   

18.
Optical microscopy, X-ray diffraction (XRD), and back-scattered electron imaging (BSE) have been used to determine the mineralogical composition of the uraniferous iron and manganese oxides and the associated U-minerals hosted in biotite granite that occurred north east Gabal El Sela area south Eastern Desert, Egypt. These mineralizations were found as veinlets fractures filling associated with strongly kaolinitic alteration of the coarse-grained biotite granite. XRD determined that the geothite mineral form the main constituent of uraniferous iron oxide in addition to tapiolite, and kaolinite minerals, where as uraniferous manganese oxide composed of pyrolusite, ramsdellite, and cryptomelane. BSE confirmed that the associated uranium minerals represented by uranothorite, kazolite, and zentime in addition to columbite-bearing minerals. Uranothorite and columbite-bearing minerals are the most abundant minerals in this mineralization. Petrographically, biotite granite is composed mainly of quartz, in addition to K-feldspars, biotite and muscovite with minor zircon, garnet, apatite, uranium-rich thorite and iron oxide. Petrochemical studies and tectonic discrimination diagrams for this granite reveal that they are classified as granite to alkali feldspar granite, originated from calc-alkaline magma having peraluminous nature and developed in within-plate tectonic environment. Field radiometric measurements revealed the localization of two high radiometric anomalies associated with iron and manganese oxides, within this anomaly uranium content range from 65 to 85 ppm. Alpha Track-etch Detectors of radon gas registrations revealed high track density reach up to 15,448.7 Bq/m3.  相似文献   

19.
This paper presents the results of indoor radon concentration measurements in 120 dwellings of district Sudhnuti of Azad Kashmir. Measurements were taken with CR-39 passive alpha track detector. CR-39 based box type radon detectors were installed in a bedroom and living rooms of each house. The detectors were retrieved after exposing to indoor radon for period of 6 months and then etched in 6 M NaOH at 80°C for 16 h, the observed track densities were converted in to the indoor radon concentration. Indoor radon concentration varied from 20 ± 12 to 170 ± 4 Bq m−3 for the houses of the district Sudhnuti. Arithmetic mean (AM), geometric mean (GM) and geometric standard deviations (GSD) were found to be 82 ± 6, 77 ± 6 and 1.51, respectively. The minimum value of weighted average radon concentration was recorded in one of the house of Mang town, whereas the maximum value was found in the Pattan Sher Khan region. Doses due to indoor radon exposure vary from 0.50 ± 0.31 to 4.28 ± 0.11 mSv year−1 AM, GM and GSD. of mean effective doses were found to be 2.06 ± 0.13, 1.95 ± 0.18 and 1.51, respectively. According to the recommendations made by the Health Protection Agency, UK (200 Bq m−3) all the houses surveyed are within the safe limits.  相似文献   

20.
Several radioactive anomalies due to uranium and thorium, associated with the mesedimentary enclaves (Archaean) within granite (Archaean to Early-Proterozoic) have been recorded in parts of Karimnagar Granulite Terrain, Karimnagar Dist. At Peddur and Kottur, Uraninite has been identified in the samples of metasediments. The metasediment from these two places have been subjected to granulite facies of metamorphism and host high values of uranium with negligible thorium. In Peddur, samples of metasediments have assayed as high as 1.96% U3O8 with negligible thorium, and in Kottur up to 0.059% U3O8. Leaching studies on these samples have indicated that most of the U3O8 present is leachable. This discovery has opened up the possibility of finding uranium mineralisation in Archaean metasediments and thus provides a thrust for uranium exploration in similar geological environs in India. Further, the basement granite along with the metasedimentary enclaves has the potential to act as a provenance for a possible unconformity type or sandstone type U-deposit in the rocks of overlying Pakhal and Gondwana Supergroup, in Pranhita-Godavari Basin, situated to the east of this area.  相似文献   

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