Levels Of Natural Radionuclides Research Articles

Radiological implications of NORM in the production of rare-earth compounds

The composite rare earth chloride produced from monazite contain low levels of natural radionuclides and is being used as the input material for the production of individual rare earth compounds which have wide applications. Gross alpha, beta and 228 Ra activity concentrations in composite rare earth chloride and individual rare earth compounds such as oxides of Ce, Nd, Pr, Sm, Gd etc are presented. The significant radionuclide of environmental concern is identified as 228 Ra and the activity level varied between 0.1 and 7.8Bq.g −1 in different compounds. Sporadic 228 Ra levels up to 16Bq.g −1 was observed in Lanthanum oxide. The external gamma exposure rates and airborne activity due to thorium and thoron progeny in the process locations are studied. The activity levels in liquid effluent and potential exposure scenarios are indicated. Radiation protection and management of wastes generated by industries that process minerals and raw materials containing naturally occurring radioactive materials (NORM) are of concern in the context of long term environmental implications of waste disposal. Chemical compounds of rare-earth (RE) elements (La to Lu) have wide applications in daily life. They are commercially exploited from minerals such as monazite, bastnasite, xenotime, allanite etc. Most of these natural ores and minerals contain low or significant levels of thorium and uranium series nuclides. The thorium content varies from 0.1% to 10% and uranium content varies from very low percentage to 0.8% depending on the mineral and region of occurrence (1). Monazite (Ce,La,Th)PO4, a phosphate mineral containing nearly 9% thorium as ThO2 is the starting material for the production of rare earth compounds in India. Caustic digestion followed by selective extraction in HCl is the method used to separate composite rare-earths chloride. Limited studies on the radiation protection aspects in rare-earths industry are reported (2, 3). A variety of diversified RE compounds that have wide applications in daily life and advanced scientific research are produced from the composite RE chloride by different chemical processes such as precipi- tation, solvent extraction and ion-exchange methods. The present studies are carried out in a rare-earths producing plant typically convert composite RE chloride to different compounds such as RE fluoride, oxide, carbonate and other individual rare earths compounds with emphasis on radiological aspects.

Occupational radiation exposure due to norm in a rare-earth compounds production facility

In India, rare-earth compounds are produced from the beach sand mineral monazite. Caustic digestion of the mineral followed by selective acid extraction is the method used to separate composite rare-earth fraction. The composite rare-earth chloride contains low levels of natural radionuclides and is the starting material for individual rare-earth compounds which have wide applications. Activity concentrations in composite rare-earth compounds such as chlorides, fluorides, carbonates and oxides of Ce, Nd, Pr, Sm, Gd, etc. are presented in this paper. The external gamma exposure rates and airborne activity due to thorium and thoron progeny in the occupational environment are studied. The activity levels in liquid effluent are presented. The potential individual occupational dose is estimated to be 1.9 mSv per annum.

Radiological impact in an area of elevated natural radioactivity background: the case of the island of Ikaria–Aegean Sea, Greece

The levels of natural radionuclides in metallic spring water (either for spa and household use), potable water (local domestic network), soil and rock samples were measured in the island of Ikaria in the Aegean Sea, Greece. The concentrations of 222Rn and natural γ emitters were found to be significantly elevated in spring water and some soil and rock samples. The external and internal dose rates (μSv year −1) were estimated in three critical groups according to the water use. The maximum external dose rates were found to be at the upper limits of the levels reported in the literature. Moreover, high dose rates were estimated for the workers in spa installations.

Levels of natural radionuclides in some Nigerian cereals and tubers

The activities of radionuclides in the two major groups of foodstuff widely consumed in Nigeria have been determined. The 40K concentration range from 9.9 ± 3.6 Bq kg −1 to 298 ± 14 Bq kg −1 (av. 130 ± 8.12 Bq kg −1). 238U concentration range from 1.47 ± 0.91 Bq kg −1 to 39.5 ± 9.9 Bq kg −1 (av. 11.5 ± 3.86 Bq kg −1), and 232Th range from 3.50 ± 1.85 Bq kg −1 to 10.5 ± 2.13 Bq kg −1 (av. 6.78 ± 2.13 Bq kg −1). 137Cs was not detected in any of the foodstuffs analysed.

Concentrations of natural radionuclides in imported mineral substances

Levels of natural radionuclides, such as thorium-232 ( 232Th), radium-226 ( 226Ra) and potassium-40 ( 40K), were determined in about 2000 samples of imported mineral substances using gamma spectrometry. The maximum concentration levels of 232Th, 226Ra and 40K were 1260±54, 13400±94 and 1256±260 Bq kg −1, respectively, in zirconium compounds. Due to relatively high concentrations of the above-mentioned radionuclides in some imported mineral substances, the National Radiation Protection Department (NRPD), as the competent authority, has established national limits (900 Bq kg −1 for 232Th, 1800 Bq kg −1 for 226Ra and 11000 Bq kg −1 for 40K), based on the external exposures, for general importation permits of these materials.

Monitoring of natural radioactivity in working places

Radioactive materials are treated and transformed mainly in nuclear industries. However, non-nuclear industries use raw materials containing significant levels of natural radionuclides; the processing of these materials can expose workers and people living near such sites to radiation levels well above the natural background. This radioactivity is due to nuclides belonging to the 238U and 232Th decay chains and to 40K. Inductively coupled plasma mass spectrometry (ICP-MS) and gamma-ray spectrometry have been used together to determine uranium and thorium concentration and the conditions of secular equilibrium in their decay chains for samples from ceramic and phosphate-fertiliser plants. In fact, the knowledge of the secular equilibrium conditions is necessary in order to make correct assumptions for the dose assessment. The results indicate that the secular equilibrium is verified for the samples from ceramic plants, whereas a situation of disequilibrium between parents and daughters of the natural chains is detected in phosphate fertilisers.

Natural radionuclides in the aquatic environment of a phosphogypsum disposal area

Rock phosphate ore processing and disposal of phosphogypsum contribute to enhanced levels of natural radionuclides in the environment. Studies on the distribution of U-series nuclides were carried out in the Chitrapuzha River, near Cochin, in the southern part of India. The concentrations of radionuclides, especially 226 Ra , in the river waters showed enhancement by an order of magnitude relative to the levels in nearby water bodies. The concentrations were influenced by seasonal changes in the river flows during monsoon and summer periods. Ingestion doses via fish and milk have an upper estimate of 18 μSv for the critical population.

Spatial analysis of natural radionuclides in peat overlying a lithological contact in Co. Donegal, Ireland

The Cronamuck Valley lies on the north-eastern contact of the Barnesmore pluton in Co. Donegal and has been identified as a region with elevated levels of natural radionuclides during a programme of uranium prospecting in the region, conducted in the 1970s. As part of a radiological survey of the area carried out by the Institute of Technology, Sligo the spatial distribution of 238U, 226Ra, 228Ra and 40K in the valley was investigated using geostatistical methods. Radionuclide levels in sixty soil samples were determined using high-resolution gamma-ray spectrometry. 238U levels ranged from 2.7 to 788 Bq kg -1 with a mean value of 79 Bq kg -1, 226Ra levels ranged from 4 to 479 Bq kg -1, with a mean value of 104 Bq kg -1, 228Ra levels ranging from 3 to 135 Bq kg -1 with a mean of 35 Bq kg -1 and 40K activities ranged from 8 to 1088 Bq kg -1 with a mean value of 526 Bq kg -1. Standard deviations for the radionuclide distributions were 149.9, 125.5, 25.1 and 278.1 Bq kg -1, respectively. Isopleth maps of the radionuclide activities were constructed using geostatistical techniques. These indicate strong geological control over soil radionuclide levels in the region, the highest activity values occurring in the granite area, and provide evidence of the immobility of natural radionuclides in organic soils.

Levels of Natural Radionuclides in Human Excreta in the Berlin Area

The determination of radionuclides in human excreta is one method for monitoring the internal exposure of workers handling radioactive material. For the purposes of calculating the internal dose from such exposures one has to consider the natural background caused by the ubiquitous but area-dependent exposure to natural radionuclides. This is especially true of monitoring of the exposure to long-lived natural radionuclides of the 238 U and 232 Th series. To get a first impression of the natural background of some of these radionuclides the amount of various natural radionuclides present in faeces and urine of non-exposed persons from Berlin were measured. In the faecal samples, each collected over a period of 24 h, the following levels were found: uranium ranged from 0.4 to 2.2 μgFd -1 mean 1.4 μg.d -1 226 Ra from 38 to 121 mBq.d -1 , mean 65 mBq.d -1 , 210 Pb from 52 to 185 mBq.d -1 , mean 111 mBq.d -1 , 232 Th from 1.6 to 12 mBq.d -1 , mean 5.4 mBq.d -1 , 230 Th from 1.7 to 16 mBq.d -1 , mean 9.8 mBq.d -1 , and 228 Th ranged from 11 to 39 mBq.d -1 , mean 23 mBq.d -1 . Ten 24 h urine samples were analysed to determine 210 Pb and 210 Po. Only one value for 210 Pb and six for 210 Po were above the detection limit of 6 mBq.l -1 and 2 mBq.l -1 , respectively. The highest value for 210 Po was at 10 mBq.d -1 .

Protection against occupational exposure to natural sources

AH forms of life are unavoidably exposed to radiation from natural sources. Over the past decade, a gowing awareness with regard to potential hazard incurred at work as a consequence of this natural radioactivity has emerged. Considering that this exposure should reasonably be regarded in certain circumstances as being the responsibility of operating management, the Intemal commission on radio- logical protection (ICRP) provided some practical guidance on good practices in this field in iis recent publications. One key question however remains to iden- tify properly the situations in which expasure from natural sources should be inclu- ded as part of occupational exposure and possibly subject to the same degree of control as those from artincial radiation sources. This paper intends to mess the scope of the problem and to review recent data reported on exposure which may occur in different workplaces due to natural sources: radon, material with ele- vated levels of natural radionuclides and cosmic radiation.

Uranium in Humans

Abstract Measurements of the environmental and metabolic behaviour of the naturally occurring radionuclides have provided necessary information on the behaviour of stable elements and have been useful analogues in the study of man-made radionuclides. Uranium has been studied primarily because of its role in the nuclear industry and its possible effects as a heavy metal in occupational exposure cases. There is abundant literature dealing with uranium studies in animals, and some literature on human studies with chronically ill patients. Relatively few data are available which document the uranium concentrations in humans under chronic, low level environmental conditions. Some recent bone measurements performed at the US Department of Energy, Environmental Measurements Laboratory are presented. For comparison, a summary of published information on uranium concentrations in blood, soft tissues and bones of humans is also presented. These data are selected to eliminate results from areas of known elevated natural radionuclide levels and occupational or controlled experimental exposure cases. From the measurements of the uranium concentration in bone from 12 countries, it is possible to derive a cumulative frequency distribution for the sampled populations.

The Distribution of Natural Radionuclides in Native Soils of Southern Saskatchewan, Canada

AbstractLittle information is available on the regional distribution of natural radionuclides in agricultural environments. Surface soil samples were collected from uncultivated, unfertilized sites in the agricultural area of Saskatchewan, Canada, and analyzed for 40K, and daughters of 238U and 232Th. Activities of 40K, 214Bi (238U daughter), and 208Tl (232Th daughter) were normally distributed with means of 480, 19, and 8 Bq kg−1, respectively. Overall, the activities of all three radionuclides decreased as soil texture became coarser, while distinct geographic areas with elevated levels were probably due to local parent material composition. Natural radionuclide levels were significantly correlated to one another and the average ratio of 214Bi/208Tl/40K in native, unfertilized Saskatchewan surface soils was 1:0.45:26.

Natural radionuclides in mineral waters

Concentration levels of natural radionuclides in mineral waters have been studied in several European countries. In the Federal Republic of Germany in recent years a nationwide investigation was carried out by several institutions. The concentrations of 226Ra, uranium isotopes, 210Pb and 210Po found are similar to those in other European countries. While for adults the health risk from drinking mineral water is comparable to the risk from terrestrial radiation, special consideration has to be given to the risk of infants when mineral water is used for preparing their food.

Gross alpha and beta radioactivities associated with aquatic environments of Upper-East Tennessee impacted by industrial and mining activities

Gross alpha and beta radioactivities present in water, sediments, and macrophytes from several surface water systems in Upper-East Tennessee impacted by industrial and mining concerns were monitored during 1982. Additional samples were collected from surface water systems in the region not impacted by industrial and mining activities in order to measure the levels of natural radionuclides. Concentrations measured in surface waters were significantly lower than concentrations permitted by the U.S. Environmental Protection Agency. Sediment sample measurements indicated the presence of high natural levels of radionuclides in several of the surface water systems studied. Possible radiological contamination of sediment was identified below both of the industrial concerns in the region which process radioactive materials. Measurements of gross radioactivities in aquatic vegetation indicated extremely high levels; particularly, in macrophytes present in the surface water system immediately below a nuclear fuel fabrication facility. The levels of radioactivity present in one plant species were almost 11,000 times the levels in the surrounding water for alpha radioactivity and in excess of 7,000 times for beta radioactivity. Significant gamma radioactivity was also observed in smallmouth bass tissues harvested from this surface water system.