Primordial Radionuclides Research Articles

Effect of Geology on Soil Radioactivity and Risks to Humans Based on Data from Several Towns in Nigeria

Gamma ray spectrometric technique has been used to determine activity concentrations of some primordial radionuclides in the naturally occurring uranium, actinium and thorium series and of non-series 40K in soil samples collected from five major towns in Oyo State, Southwestern Nigeria. Activity concentration determination was done using a high purity germanium (HPGe) detector. It ranged from 85.83 ± 4.04 Bq kg−1 to 1,850.60 ± 36.83 Bq kg−1 for 40K; 5.23 ± 0.34 Bq kg−1 to 198.31 ± 4.10 Bq kg−1 for 208Tl (indicator for 232Th) and 7.82 ± 0.42 Bq kg−1 to 64.65 ± 2.00 Bq kg−1 for 214Bi (indicator for 238U). The outdoor absorbed dose rate in air due to each of the primordial radionuclides was calculated from the mean values of the activity concentration in each sample. Values ranged from 3.60 ± 0.17 nGy h−1 to 77.73 ± 1.55 nGy h−1 for 40K, 3.48 ± 0.23 nGy h−1 to 132.07 ± 2.73 nGy h−1 for 208Tl and 3.35 ± 0.21 nGy h−1 to 27.73 ± 0.86 nGy h−1 for 214Bi. The absorbed dose rate in air was the highest for rocky areas, while the lowest value came from non-rocky, non-industrialized areas. The estimated annual outdoor effective dose equivalents for the two rocky areas were 385.76 μSv y−1 and 221.28 μSv y−1. The estimated annual outdoor effective dose equivalents for the two industrialized areas were 64.05 μSv y−1 and 47.65 μSv y−1. The value for non-rocky, non-industrialized areas was 19.19 μSv y−1. The average value for the study area was 147.59 μSv y−1. The estimated collective effective dose equivalent for the area was 9.77 × 102 man-Sv y−1. The expected number of people in the study area at risk of incurring cancer per year as a result of radioactivity in the soil was estimated to be 11; this value represents approximately 7% of the estimated 160 people for 18 Nigerian cities, approximately 69% of 16 people estimated for oil producing areas of Nigeria and less than the United States Environmental Protection Agency regulatory limit of 1 cancer case to 10,000 people. Also, this result shows that local variability of natural radionuclides in soil depends on local geology of the area. The incidence number was 2.4 people per million.

Radioactivity and associated radiation hazards in ceramic raw materials and end products

Studies have been planned to obtain activity and associated radiation hazards in ceramic raw materials (quartz, feldspar, clay, zircon, kaolin, grog, alumina bauxite, baddeleyite, masse, dolomite and red mud) and end products (ceramic brick, glazed ceramic wall and floor tiles) as the activity concentrations of uranium, thorium and potassium vary from material to material. The primordial radionuclides in ceramic raw materials and end products are one of the sources of radiation hazard in dwellings made of these materials. By the determination of the activity level in these materials, the indoor radiological hazard to human health can be assessed. This is an important precautionary measure whenever the dose rate is found to be above the recommended limits. The aim of this work was to measure the activity concentration of (226)Ra, (232)Th and (40)K in ceramic raw materials and end products. The activity of these materials has been measured using a gamma-ray spectrometry, which contains an NaI(Tl) detector connected to multichannel analyser (MCA). Radium equivalent activity, alpha-gamma indices and radiation hazard indices associated with the natural radionuclides are calculated to assess the radiological aspects of the use of the ceramic end products as decorative or covering materials in construction sector. Results obtained were examined in the light of the relevant international legislation and guidance and compared with the results of similar studies reported in different countries. The results suggest that the use of ceramic end product samples examined in the construction of dwellings, workplace and industrial buildings is unlikely to give rise to any significant radiation exposure to the occupants.

Kernel-Based Machine Learning for Background Estimation of NaI Low-Count Gamma-Ray Spectra

Virtually all gamma-ray spectrometry measurements contain background components due to the ubiquitous presence of primordial radionuclides in the Earth's crust and cosmic radiation interactions high in the Earth's atmosphere. In principle, spectral signatures due to radiation source(s) of actual interest can be extracted from the measured gamma-ray spectrum by background subtraction. However, if separate background measurements are unavailable or infeasible, and particularly for measurements exhibiting low signal-to-noise ratio (SNR), background subtraction is nontrivial, and it requires accurate background estimation . An example application of gamma-ray spectroscopy with low SNR is the “source search” scenario, where the position of a source is sought using measurements taken over very short time intervals by a detector in motion. We have developed an algorithm for background estimation in low-count gamma-ray spectra using kernel-based Gaussian processes (GP) taken from the field of machine learning. We have evaluated the performance of our algorithm using a group of three kernels tested against a dataset composed of background spectra measured in an urban environment using a mobile sodium iodide (NaI) detector. We have also simulated datasets containing nonbackground gamma-ray sources in an urban background measured with a NaI detector. The simulated scenarios employed a variety of source-detector distances and different types of source shielding. As a metric of algorithm performance, we calculated correlation coefficients, Theil inequality coefficients, and count difference statistics between estimated and actual backgrounds. We concluded that our method adequately estimates the gamma-ray background, but we also observed a strong dependence of the algorithm's performance on the selected kernel.

Natural radioactivity and associated radiation hazards of some commonly used building materials in southwest Nigeria

The activity concentrations of primordial radionuclides ( 40 K, 226 Ra and 232 Th) in five different types of commonly used building materials in southwest Nigeria were measured using a low-background NaI(Tl) detector coupled to an IBM-compatible multichannel analyzer. The highest mean concentration of 40 K, which was 887.5 ± 101.3 Bq.kg -1 , was obtained in gravel. Also, the highest mean concentrations of 226 Ra and 232 Th were obtained, respectively, in sand and brick samples. The lowest mean concentrations of 40 K, 226 Ra and 232 Th, respectively, were obtained in brick and cement sample. The annual gonadal effective dose (AGED) and other radiological parameters were estimated from the activity concentrations of the radionuclides. The highest mean values of the AGED and radium equivalent activity concentration obtained were 359.1 μSv.y -1 and 110.9 Bq.kg -1 , respectively. All these radiological parameters were below the maximum permissible levels recommended for safe use of materials in building construction. It can therefore be concluded that these materials do not pose any radiological hazard to the dwellers of buildings constructed with them.

Background in the context of land contaminated with naturally occurring radioactive material

The financial implications of choosing a particular threshold for clearance of radioactively contaminated land are substantial, particularly when one considers the volume of naturally occurring radioactive material (NORM) created each year by the production and combustion of fossil fuels and the exploitation of industrial minerals. Inevitably, a compromise needs to be reached between the level of environmental protection sought and the finite resources available for remediation. In the case of natural series radionuclides, any anthropogenic input is always superimposed on the inventory already present in the soil; this ‘background’ inventory is conventionally disregarded when assessing remediation targets. Unfortunately, the term is not well defined and the concept of ‘background dose’ is open to alternative interpretations. In this paper, we address the issue of natural background from a geochemical rather than from a solely radiological perspective, illustrating this with an example from the china clay industry. We propose a simple procedure for decision making based on activity concentrations of primordial radionuclides and their progeny. Subsequent calculations of dose need to take into account the mineralogical and chemical characteristics of the contamination, which in the case of NORM are invariably reflected in uranium series disequilibrium.

Implication and hazard of radiation level in the building materials

The natural radioactivity due to radium, thorium, and potassium in building material samples contribute to the radiation dose received by human beings significantly. It is essential to evaluate the activity levels of these nuclides for the assessment of natural radiation dose. Activity concentrations of the gamma emitting primordial radionuclides 232Th, 226Ra, and 40K were measured using high resolution gamma spectrometry technique with high purity germanium (HPGe) detector in building materials: sand, brick, granite, cement and rock, collected from various areas of Gulbarga and Koppal districts. The standard ASTM procedure was followed for the sample preparation. The distribution of radionuclides and variation in activity concentration depend upon the rock formation and the geological properties of the region. The activity of the three radionuclides, 232Th, 226Ra, and 40K, were found to be in the range of 3.1–227.1, 1.6–111, and 23.2–1505 Bq/kg, respectively. The dose related radiological parameters were also calculated for all the samples and the observations show that the activity concentrations of the radionuclides are well within the UNSCEAR limits.

A review on natural background radiation

The world is naturally radioactive and approximately 82% of human-absorbed radiation doses, which are out of control, arise from natural sources such as cosmic, terrestrial, and exposure from inhalation or intake radiation sources. In recent years, several international studies have been carried out, which have reported different values regarding the effect of background radiation on human health. Gamma radiation emitted from natural sources (background radiation) is largely due to primordial radionuclides, mainly 232Th and 238U series, and their decay products, as well as 40K, which exist at trace levels in the earth's crust. Their concentrations in soil, sands, and rocks depend on the local geology of each region in the world. Naturally occurring radioactive materials generally contain terrestrial-origin radionuclides, left over since the creation of the earth. In addition, the existence of some springs and quarries increases the dose rate of background radiation in some regions that are known as high level background radiation regions. The type of building materials used in houses can also affect the dose rate of background radiations. The present review article was carried out to consider all of the natural radiations, including cosmic, terrestrial, and food radiation.

Radiopurity of a CeBr3 crystal used as scintillation detector

Cerium bromide (CeBr3) has recently been shown to exhibit several properties making it a suitable material as a scintillation detector in nuclear physics applications. The intrinsic activity of gamma-ray emitting radionuclides in a 38.1mm×38.1mm (diameter×height) crystal of CeBr3 was investigated. The measurements were carried out in the HADES underground laboratory located 225m underground. Two primordial radionuclides were detected; 227Ac (and its daughters) with massic activity of 0.30±0.02Bq/kg and 138La with massic activity of 7.4±1.0mBq/kg. Two activation products were also detected; 139Ce and 82Br. Their massic activities (assuming a homogeneous distribution in the crystal) just before taking the CeBr3 crystal underground were 4.3±0.3mBq/kg and 18±4mBq/kg correspondingly. None of the other common primordial radionuclides (40K, 226Ra, 228Ra, 228Th, and 235U) were detected and their detection limits were below 2mBq/kg except for 238U for which the upper limit was 135mBq/kg and 210Pb with an upper limit of 600mBq/kg.

Primordial radioactivity (238U, 232Th and 40K) measurements for soils of Ludhiana district of Punjab, India

The aim of the present work was to study the activity concentration and absorbed gamma dose rates due to primordial radionuclides ((238)U, (232)Th and (40)K) for the soil of different villages of Ludhiana district of Punjab, India using a high-purity germanium detector based on high resolution gamma-ray spectrometry. The average activity concentrations of (238)U, (232)Th and (40)K in the soil samples have been found to be 28.58, 50.95 and 569.59 Bq kg(-1), respectively, which gives the total gamma dose rate contribution of 68.50 nGy h(-1). To evaluate the radiological hazard of the natural radioactivity, the radium equivalent activity, the external hazard index, the absorbed dose rate and the effective dose rate have been calculated. The calculated radium equivalent activity values are on the lower side of the recommended safe limit value of 370 Bq kg(-1) by Organization of Economic and Control Department. The calculated value of external health hazard index is lower than unity.

Radiometric analysis of construction materials using HPGe gamma-ray spectrometry

Concentrations of primordial radionuclides in common construction materials collected from the south-west coastal region of India were determined using a high-purity germanium gamma-ray spectrometer. Average specific activities (Bq kg(-1)) for (238)U((226)Ra) in cement, brick, soil and stone samples were obtained as 54 ± 13, 21 ± 4, 50 ± 12 and 46 ± 8, respectively. Respective values of (232)Th were obtained as 65 ± 10, 21 ± 3, 58 ± 10 and 57 ± 12. Concentrations of (40)K radionuclide in cement, brick, soil and stone samples were found to be 440 ± 91, 290 ± 20, 380 ± 61 and 432 ± 64, respectively. To evaluate the radiological hazards, radium equivalent activity, various hazard indices, absorbed dose rate and annual effective dose have been calculated, and compared with the literature values. Obtained data could be used as reference information to assess any radiological contamination due to construction materials in future.

Distribution of terrestrial gamma radiation dose rate in the eastern coastal area of Odisha, India

Terrestrial gamma radiation is one of the important radiation exposures on the earth's surface that results from the three primordial radionuclides (226)Ra, (232)Th and (40)K. The elemental concentration of these elements in the earth's crust could result in the anomalous variation of the terrestrial gamma radiation in the environment. The geology of the local area plays an important role in distribution of these radioactive elements. Environmental terrestrial gamma radiation dose rates were measured around the eastern coastal area of Odisha with the objective of establishing baseline data on the background radiation level. The values of the terrestrial gamma radiation dose rate vary significantly at different locations in the study area. The values of the terrestrial gamma dose rate ranged from 77 to 1651 nGy h(-1), with an average of 230 nGy h(-1). During the measurement of the terrestrial gamma dose rate, sand and soil samples were also collected for the assessment of natural radionuclides. The activities of (226)Ra, (232)Th and (40)K from these samples were measured using a gamma-ray spectrometry with a NaI(Tl) detector. Activity concentrations of (226)Ra, (232)Th and (40)K ranged from 15.6 to 69 Bq kg(-1) with an average of 46.7 Bq kg(-1), from 28.9 to 973 Bq kg(-1) with an average of 250 Bq kg(-1) and from 139 to 952 Bq kg(-1) with an average of 429, respectively. The detailed significance of these studies has been discussed from the radiation protection point of view.

Anthropogenic Radionuclides in Ottawa River Sediment near Chalk River Laboratories

The Ottawa River has received nuclear reactor effluent from Chalk River Laboratories (CRL) for more than 60 years, including releases from a NRX accident in 1952. Recent interest in the potential impact of these historical releases and the possible need for remediation of a small region immediately downstream from the release point has led to comprehensive studies to assess risk to people and wildlife. In this paper, the results of an extensive survey of gamma-emitting anthropogenic radionuclides in Ottawa River sediment in the vicinity of CRL are presented. Anthropogenic radionuclides detected in Ottawa River sediment include 60Co, 94Nb, 137Cs, 152Eu, 154Eu, 155Eu and 241Am. Concentrations of all anthropogenic radionuclides decline rapidly with distance downstream of the process outfall, reaching stable concentrations about 2 km downstream. All of these radionuclides are found at some sites within 2 km upstream of the process outfall suggesting limited upstream transport and sedimentation. Comparison of anthropogenic radionuclides with several representative primordial radionuclides shows that with the exception of sites at the process outfall and within 2 km downstream of the process outfall, primordial radionuclide concentrations greatly exceed CRL derived anthropogenic radionuclide concentrations. Thus, over 60 years of radionuclide releases from operations at CRL have had little impact on radionuclide concentrations in Ottawa River sediment, except at a few sites immediately adjacent to the process outfall.

Geological and radiological studies of the Mount Arafat, Mekkah, Saudi Arabia

Mount Arafat is a sacred place for Muslims. It has been classified as a granodiorite rock which mainly consists of feldspar and quartz, muscovite, etc. During the Hajj and Umra, Muslims visit this holly place and stay there for some time. In order to study the geology and thermal history as well as to assess the radiological hazards due to the presence of primordial radionuclides, systematic studies using petrographic, fission track dating and γ-spectrometric (HPGe) techniques were carried out. Our study yielded fission track age of 9.13 ± 1.05 Ma of the Mount Arafat granodiorite. Rifting, magmatism, volcanism and sea floor spreading that resulted in the formation of Red Sea seems may have altered the original age of the Arafat granodiorite under study to 9.13 ± 1.05 Ma. Measured radioactivity concentrations due to 226Ra, 232Th and 40K were found to be 10.75 ± 3.92, 29.21 ± 4.34 and 664.49 ± 7.45 Bq kg−1, respectively. From the measured radioactivity, gamma index (Iγ) and radium equivalent (Raeq) were calculated as 0.402 and 103.23 Bq kg−1 whereas outdoor external dose (Dout) and annual effective dose (Eout) were estimated to be 40.30 nGyh−1 and 0.045 mSvy−1 respectively. All the above mentioned values are well below the recommended limits. The Mount Arafat thus does not pose any radiological health hazard to the general public.

Radioactivity measurement of primordial radionuclides in and dose evaluation from marble and glazed tiles used as covering building materials in Turkey

Measurements of the natural radioactivity arising from primordial radionuclides ((226)Ra, (232)Th and (40)K) in marble and glazed tile samples used covering building materials in Turkey were carried out by gamma-ray spectrometer with a high purity germanium detector. The mean activity concentrations of the (226)Ra, (232)Th and (40)K in marble and glazed tile samples were found as 8.2, 5.5 and 58.1 Bq kg(-1) and 81.2, 65.4 and 450.1 Bq kg(-1), respectively. The radiation doses received by occupants of buildings in which the sample marble and glazed tiles might be used are estimated using measured activity concentrations of constituent primordial radionuclides and dose conversion factors evaluated by the European Commission from models of tile use. Results obtained are presented for each radionuclide, analysed and compared with relevant national and international legislation, guidance and report, and with the results obtained from other studies. Results show that the use of such decorative building materials in the construction of domestic homes or workplaces in Turkey is unlikely to lead to any significant radiation exposure to the occupants.

Estimation of indoor radon levels and absorbed dose rates in air for Chennai city, Tamilnadu, India

Indoor radon concentrations were measured inside different types of dwellings in Chennai city on a quarterly basis using a solid state nuclear track detector (LR-115, Type II) for 1 year. Significant seasonal variations were observed. The average highest radon concentration was observed during winter (86.08 Bq m−3) and the lowest in summer (42.50 Bq m−3). The radon concentrations were also varying on the basis of different floor-covering materials. For a given season, the average maximum radon concentration was observed with cement flooring (118.96 Bq m−3) followed by tiles (75.25 Bq m−3) and marbles (74.04 Bq m−3). Also, outdoor soil samples were collected in and around the same dwellings and determined the radioactivity content of three primordial radionuclides (238U, 232Th and 40K) in these soil samples using NaI(Tl) scintillation detector based gamma-ray spectrometer.

Measurement of gamma natural background radiation in Chamaraja Nagar district, Karnataka state, India

Background: All objects in nature are exposed to ionizing radiation emitted by primordial radionuclides and cosmogenic radionuclides due to cosmic rays, the influence of which on living beings is very imminent and important to study. The amount of this background radiation received by an individual depends on altitude, latitude type of building and the building construction materials. Materials and Methods: In the present study, measurements of natural background radiation were made in the schools, temples, dwellings, and hill stations etc., in Chamaraja Nagar District, Karnataka State, India by using Environmental Dosimeter technique. Results and Conclusion: The absorbed dose rate in dwellings of different villages in this region varies from 98.3 ± 7.1 to 708.2 ± 59.3 nGyh−1 with an average of 291.8 ± 23.4 nGyh−1 , whereas in temples it varies from 71.4 ± 5.2 to 589.0 ± 46.3 nGyh−1 with an average of 240.5 ± 19.2 nGyh−1 .

Gamma Radiation Measurements in Tunisian Marbles

The radioactivity of 15 kinds of different granites collected in Tunisia was determined by gamma-ray spectrometry using hyper-pure germanium (HPGe) detector. The average activity concentrations for primordial radionuclides 238U, 232Th and 40K were respectively 33.24, 8.01 and 116.98 Bq/kg. The activity concentrations ranged from 3.59 to 87.37 Bq/kg for 238U, from 0.45 to 25.34 Bq/kg for 232Th and from 24.06 to 380.23 Bq/kg for 40K. The measured activity concentrations were used to assess of the radium equivalent activity ranged from 22.2 to 995.8 Bq/kg, the absorbed dose rate in air from 7 to 1209 nGy/h and the internal (0.1 to 2.8) and external (0.1 to 2.7) hazard indices. The data obtained in this study may be useful for natural radioactivity mapping.

Environmental radioactivity evaluation in the coastal stretch of Bay of Bengal from Pondycherry to Velanganni (South East coast of India)

Background: Since the Madras Atomic Power Station, Kalpakkam and Kudankulam Nuclear Power Plant, Kudankulam are sited in Bay of Bengal coast, radiological study of this coastal environment is imperative to assess the impact of operation of nuclear power plant, if any, on the radioactivity profile of the coast. Materials and Methods: In the present study the environmental radioactivity was evaluated by measuring activity concentrations of primordial radionuclides namely 238 U, 232 Th and 40 K. in the beach sand samples using high purity germanium gamma ray spectrometry. 10 sampling stations were fixed along a 290 km coastal stretch of Bay of Bengal from Pondycherry to Velangannni. Results: The activity concentration of 238 U is always much less than that of 232 Th and 40 K and it ranged from 9 Bq/kg (Pondicherry coast) to 93 Bq/kg (Karaikal coast). However, 232 Th concentration fluctuated from 12 Bq/kg (Pichavaram Mangrove) to 1075 Bq/kg (Karaikal coast). The activity concentration of 40 K varied within a narrow range from 162 Bq/kg to 474 Bq/kg. The distribution of primordial radioactivity was non-uniform along the entire stretch of Bay of Bengal. The elevated levels of 232 Th were recorded in Karaikal coast (S7) (1075 Bq/kg), Tirumullaivasal coast (S4) (215 Bq/kg), and Nagapattinam coast (S9) (146 Bq/kg) and attributed to the presence of thorium-rich monazite as beach placer in coastal sands. Conclusion: The total absorbed gamma dose contributed by the activity of 238 U, 232 Th, and 40 K varied between 29 nGy/h and 308 nGy/h with a GM value of 64.4 nGy/h. Similarly, the annual effective dose recorded for Bay of Bengal ranged from 0.04 mSv/year to 0.38 mSv/year, indicating that the Bay of Bengal, in general, falls under Normal Background Radiation Area.

Determination of Primordial Radionuclides in Natural Samples Using HPGe Gamma-Ray Spectrometry

Distributions of primordial radionuclides in soil and vegetables were investigated using high-purity germanium gamma-ray spectrometry. Gamma-ray spectrometry is one of the most accepted and widely used techniques for the detection and analysis of radioactive materials for a wide range of activity. Important properties of the employed gamma-ray detector were also determined to ensure the accuracy of the radiometric analysis. The studied samples were kept in airtight condition at least for 6 weeks before gamma counting to attain the radioactive equilibrium between daughters and parents of 226Ra (238U) and 232Th decay series. The average specific activities for uranium in soil and vegetable samples were obtained as 21±4 and 2.4±0.4, respectively. Respective values for Thorium and Potassium levels were obtained as 21±3, 1.9±0.5 and 290±20, 80.3±54.9 in soil and vegetable samples. The reported data can be considered as base values for distribution of natural radionuclides in soil and vegetable samples in the studied region, and will be used as reference information to assess any radiological contamination due to soil and vegetables in future. The response of the studied the detector was found suitable for radioactivity analysis of natural samples having a wide range of activity.

A Study on Natural Radioactivity in Khewra Salt Mines, Pakistan

The Khewra Salt Mines, the second largest salt mines in the world, are located 160 km south of Islamabad, the capital of Pakistan. Around 1000 workers are involved in the removal of salt from these mines. More than 40,000 visitors come annually to see the mines. The visitors and workers are directly exposed to the internal and external radiological hazards of radon and gamma rays in these mines. The general public is affected by the intake of the salt containing the naturally occurring radionuclides. Therefore the concentration of radon (²²²Rn) in the Khewra Salt Mines and activity concentrations of the naturally occurring radionuclides in the salt samples from these mines were measured. Both active and passive techniques were employed for the measurement of radon with Radon Alpha Detector (RAD-7) and SSNTD respectively. The concentration of ²²²Rn was 26 ± 4 Bq m⁻³ measured by the active method while 43 ± 8 Bq m⁻³ was measured by the passive method. The activity concentration of the radionuclides was measured using gamma ray spectrometry with HPGe detector. The mean activity of ⁴⁰K in salt samples was found to be 36 ± 20 Bq kg⁻¹ and the concentration of ²²⁶Ra and ²³²Th in the salt samples was below the detection limits. Gamma radiation hazard was assessed in terms of the external gamma dose from salt slabs and the rooms made of salt and the annual effective dose due to gamma radiation. The exposure to radon daughters, annual effective dose and excessive lifetime cancer risk due to radon in the mines were estimated. The mean annual effective dose due to an intake of ⁴⁰K from the salt was calculated as 20.0 ± 11.1 µSv, which is lower than the average annual effective dose rate of 0.29 mSv, received by the ingestion of natural radionuclides. Due to the low concentration values of primordial radionuclides in the salt and radon ²²²Rn) in the mines, a 'low level activity measurement laboratory' is suggested to be established in these mines.