Natural Background Dose Research Articles

96/05506 Dose rate conversion factors, soil thickness and their influence on natural background dose rate in air above carbonate terrains

96/05506 Dose rate conversion factors, soil thickness and their influence on natural background dose rate in air above carbonate terrains

Environmental Radiometry Around Coal Mining Wastes Using MCP-N (LiF:Mg,Cu,P) Detectors and Gamma-Ray Spectrometry

Natural gamma background dose rates 1 m above ground level were evaluated using MCP-N detectors (LiF:Mg,Cu,P, produced at INP Krakow) at over 30 points, and the natural radioactivity of samples of materials deposited at the Przezchlebie industrial stockpile gathered from some of these locations assessed off-site using gamma ray spectrometry. Measurements were made in late spring over different parts of the stockpile and the neighbouring terrain, and repeated after one year. Above-ground gamma dose rates correlated well with the activity of elements in the 232 Th and 238 U series, the 226 Ra sub-series and 40 K measured in the material samples. LiF:Mg,Cu,P (MCP-N) detectors are extremely convenient for use in environmental dosimetry as their stability and sensitivity allow field exposures to take no longer than two weeks, instead of three months required for LiF:Mg,Ti (TLD-100) detectors. This considerably speeds up measurements and may prevent theft or displacement of dosemeters in industrial conditions.

Depth-dose distribution in bricks determined by thermoluminescence and by Monte-Carlo calculation for external γ-dose reconstruction

The analysis of depth-dose distributions in bricks sampled from walls in areas with nuclear waste or accident contamination has the potential of providing information on the energy and source configuration of the γ-radiation that had been incident on the brick. In this study, a brick from a mill facing a shallow water reservoir of the contaminated Techa river in the South Ural region is investigated. Thermoluminescence (TL) methods were used to measure the accumulated dose at several depths in the brick. The accidental external γ-dose is obtained by subtracting the natural radiation background dose from the total accumulated dose. In the first segment of the brick, at a depth of about 1.5 cm, the accident dose was found to be roughly 3.5 Gy. Monte-Carlo simulations of the photon transport from the reservoir bed contaminated with 137Cs were calculated for different depths in the brick. The calculations were made assuming different attenuating water levels. It is found that the depth-dose distribution determined by measurements corresponds to a water level between 20 and 50 cm. The results indicate that TL measurements combined with Monte-Carlo modelling calculations are highly promising for external γ-dose reconstruction applications.

Dose rate conversion factors, soil thickness and their influence on natural background dose rate in air above carbonate terrains

The natural background dose rate in air above ground surface is the sum of doses arising from cosmic radiation and radionuclides in air, soil and bedrock. The resulting dose rate arising from radionuclides in soil and bedrock (ground component) is the product of characteristic radionuclides specific activity in soil or bedrock with the accompanying dose rate conversion factors (DRCF). The sum of products between unit dose rates from each emitted photon energy and the emission intensity of all accompanying radionuclides is presented with DRCF for characteristic radionuclide. DRCF are calculated for unit 40K activity in soil and bedrock as well as for unit head radionuclides activity of 232Th decay series, 235U decay series, 238U- 230Th subseries and 226Ra- 210Pb subseries, in relation to soil thickness. Presented DRCF values are generally in good agreement with those published previously, and strongly depend on soil thickness. Recalculation of ground component of natural background dose rate data collected by airborne or carborne surveys above carbonate terrains into radionuclides concentration in the ground is possible in two cases. Recalculated values present radionuclide concentrations in bedrock in the case where soil has been completely missing. In the case of well-developed soil (thickness of 25 cm or more) it represents concentrations in soil relatively well. The laboratory gamma-spectrometry of 40K, 226Ra, 228Ac or 208Tl and 238U in samples collected during conventional geochemical sampling provides a good database of characteristic radionuclides. Such a database is applicable for assessment of ground components of natural background dose rate, as well as for geochemical map constructions.

Environmental Study on Radioactivity of the Spas in the Island of Ikaria

A preliminary study has been conducted on the natural radioactivity of the thermal spas in Ikaria Island. In order to carry out this research. (a) Car-borne radiometry has been applied in the areas around the spas and an elevated average natural background dose rate, 0.14 μGy.h -1 , in comparison with other Greek areas has been measured. (b) The activity concentrations of the natural radionuclides of the 238 U- 226 Ra and 232 Th decay series, as well as 40 K, in spa water, soil, sediment, surface sea water and marine flora samples in the areas of the spas were measured and the distribution of these radionuclides in the abiotic materials was evaluated. (c) The effective dose equivalent due to the consumption of spa drinking water has been estimated. This first evaluation shows that elevated activity concentrations of the environmental abiotic materials are present, which are reflected in the concentrations observed in marine flora. Based on experimental data for the main areas of interest, the observed range of dose rate for the population due to the natural radioactivity of the environmental abiotic component is 175-3133 μSv.y -1 . This seems to be higher than other Greek areas. The effective dose equivalent due to the drinking water is also found to be enhanced when compared with the respective values reported in the literature.

Some Problems of the Radiometric Mapping of Carbonate Terrains - An Example From Istria (Croatia)

The gamma dose rates were calculated from the results of gamma-spectrometric measurements of radionuclide concentrations in soils in the region of the Istrian peninsula, Croatia. Calculated gamma dose rate conversion factors (GDRCF) for external exposure above ground, give external dose rates per unit of natural radionuclide concentration in the soil and bedrock. GDRCF in air at a height of 100 cm above ground are tabulated for 40K, 232Th decay series, 238U - 230Th subseries and 226Ra - 210Pb subseries for various source depths in soil or bedrock up to a maximum depth of 120 cm. The radiometric maps must take into consideration gamma doses from soils as well as from underlying rocks in the first metre of ground profile. This is of crucial importance especially for carbonate terrains, where the differences between natural radionuclide concentrations in carbonate derived soils and carbonate bedrock could be of two orders of magnitude. Furthermore, for soils themselves the role of the drainage network in migration processes is undoubtedly very important. All these dependencies make us believe that gamma-spectrometric measurements and related dose rate conversions in connection with in situ dose measurements could be the best method for radiometric mapping at least for carbonate terrains with numerous rock outcrops, poor drainage and lithological variability on a local scale. Recalculation of natural background dose rate data, collected by airborne or carborne surveys, into radionuclide concentration in the ground in carbonate terrains is possible in two cases only: when soil is completely absent or where soils are well developed (thicknesses of 25 cm or more).

Interventional radiologists: occupational radiation doses and risks.

Interventional radiologists receive nonuniform occupational radiation doses, with relatively high doses to the head and extremities and low doses to the trunk, which is protected by a lead apron. Twenty-eight interventional radiologists from 17 institutions wore thermoluminescent dosimeters over their collars and under their aprons for a 2-month period. The estimated annual radiation dose was converted to effective dose as suggested by the International Commission on Radiological Protection. Effective dose is used to relate the risk associated with nonuniform dose to that associated with an equivalent uniform whole-body dose. The mean annual effective dose was 3.16 mSv (316 mrem), with a range of 0.37-10.1 mSv. The mean annual effective dose is approximately equal to the mean natural background dose of 3 mSv per year from radon and other natural sources and is only 6% of the National Council on Radiation Protection and Measurements' recommended effective dose equivalent limit of 50 mSv per year. The annual radiation risk of fatal cancer would be less than one per 10,000 for almost the entire career of an interventional radiologist.

Probabilistic Safety Assessment for the Transport of Radioactive Waste to a UK Repository at Sellafield

A study has been undertaken to provide a detailed understanding of the radiological and non-radiological risks associated with the transpott of radioactive waste from the sites at which waste is produced in the UK to a proposed deep repository at Sellafield, and to ensure that these risks meet the design targets specified by Nirex. The routine transport collective dose to members of the public was assessed to be 0.2 man.Sv per year, which is only about 0.004% of the natural background dose. Accident frequencies were calculated using event tree methodology. The radiological consequences of accidents were assessed using the probablistic computer code CONDOR. The risk expectation value was calculated to be 1.5 × 10−5 − 8.6 × 10−6 latent cancer fatalities per year (depending on the transport mode scenario). These values are significantly lower than the corresponding prediciions for non-radiological accident fatality rates, 0.05 − 0.035 fatalities per year. The radiological accident risk for the most exposed individual member of the public was assessed to be 5 × 10−11 − 1.7 × 10−11 per year, very much less than the Nirex target of 5 × 10−7 per year. Plots of societal risk were shown to lie in the region of ‘negligible risk’, as defined by the UK Health and Safety Commission for non-radioactive dangerous goods transport.

222Rn Alpha Dose to Organs Other than Lung

The alpha dose to cells in tissues or organs other than the lung has been calculated using the solubility coefficients for 222Rn measured in human tissue. The annual alpha dose equivalent from 222Rn and decay products in most tissues is a maximum of 30% of the annual average natural background dose equivalent (1 mSv) for external and internally deposited nuclides (not including the dose equivalent for 222Rn decay products to cells in bronchial airways). The dose to the small population of lymphocytes located in or under the bronchial epithelium is a special case and their annual dose equivalent is essentially the same as that to basal cells in bronchial epithelium (200 mSv) for continuous exposure to 200 Bq.m-3. The significance of this dose is uncertain because the only excess cancer observed in follow-up studies of underground miners with high 222Rn exposure is bronchogenic carcinoma.

210Pb, 137Cs and 40K in three species of porpoises caught in the eastern tropical Pacific Ocean

Long after the atmospheric nuclear weapons tests were discontinued, 137Cs has been traced in muscle tissue and livers of porpoised netted in the Pacific Ocean. Porpoises born and netted near test sites at dates closest to detonations show the highest 137Cs contents in their muscle. Caesium and potassium are correlated in their occurrence in muscle tissue and livers of porpoises. The similarity of the estimated concentration factor in muscle (30–100) with those obtained for fish characterized by the same ethological features, such as tuna, suggests that the mechanisms and rates governing caesium accumulation by the top marine predators are likely to be similar. Using a similar methodology as for the dose assessment in man, this study of porpoises has shown that 137Cs internal dose rates are significantly higher than 137Cs external dose rates, though both are much lower than the component of the natural background dose rate derived from 40K.

可搬型γ線波高分布測定システムの開発

The variations of environmental gamma radiation flux were observed by using a new portable spectrometry recording system for 1 year. Spectrum analyses by the response matrix method have provided much information, and the artificial contribution can be separated from natural back ground dose by using the Th-method or the three component method.

Iodine-129 in the environment of a nuclear fuel reprocessing plant: I. 127I and 127I contents of soils, food crops and animal products

Concentrations of 129I and 127I in soils, food crops and animal products collected in the environment of the small Karlsruhe nuclear fuel reprocessing plant (WAK) were determined by neutron activation analysis. 129I levels in all samples were found to be elevated by several orders of magnitude above current average biospheric background values. Resultant thyroid doses from consumption of food produced at locations in the vicinity of the Karlsruhe reprocessing plant are, however, small relative to the natural background dose.

Über die röntgendiagnostische Strahlenbelastung der Kinder in Spitälern und Ambulatorien

Die individuelle Strahlenbelastung der Kinder im Rahmen der Röntgendiagnostik wurde an 4 Krankenanstalten und einem Großambulatorium in Wien vergleichend geprüft.

Dose reduction in diagnostic radiology.

Recent editorials in the radiological journals have expressed the concern felt by all at the realisation of the fact that diagnostic radiology contributes the largest percentage of man-made radiation to the population. The knowledge that this is the case has been brought to our attention by the publication of the White Paper entitled The hazards to man of nuclear and allied radiations. One of the conclusions reached in this report is that “Those responsible for authorising the development and use of sources of ionizing radiation should be advised that the upper limit, which future knowledge may set to the total dose of extra radiation which may be received by the population as a whole, is not likely to be more than twice the dose which is already received from natural background; the recommended figure may indeed be appreciably lower than this.” The natural background dose is given as about 1 r per ten years. In the statement on the responsibilities of the medical profession in the use of ionizing radiation published by the United Nations Scientific Committee (1957) it is stated that the genetic radiation from diagnostic procedures is found to be equal to at least 100 per cent of all natural radiation in Sweden and in the U.S.A. An estimate of the minimum genetic dose from diagnostic procedures in Great Britain is given as at least 22 per cent of background (Osborn and Smith, 1956).