Uranium Decay Chain Research Articles

Measurement of radium, thorium, potassium and associated hazard indices from the soil samples collected from Northern India

The presence of radium, thorium and potassium in soil and building materials impose radiological hazards to human population. Both alpha and gamma radiation are produced from the decay chain of uranium and thorium while potassium is itself a source of gamma radiation. The measurement of these radionuclides in soil is important to prevent the general public from health hazards. The measurement of radium, thorium and potassium from soil samples collected from some locations of Northern India was carried out to assess the various radiological hazard indices using sodium iodide-based gamma ray spectroscopy. The observed specific activities of radium, thorium and potassium varied from 13 to 175, 141 to 399 and 276 to 1581 Bq/kg with an average of 78, 231 and 525 Bq/kg, respectively. The mean values from soil samples under study are more than the corresponding worldwide average values (35, 30 and 400 Bq kg−1 for 226Ra, 232Th and 40K) but less than the recommended limits. The measured radium, thorium and potassium activity from the soil samples were used to find out the various hazards index and absorbed dose. The results show the soil of the study area does not pose any health hazards to people residing in this area.

SOURCES OF RADIOACTIVE WASTE IN LEACH PLANTS PROCESSING URANIUM ORES

A distinctive feature of enterprises for extracting and processing uranium ore is the inevitable pollution by solid, liquid and gaseous waste. The amount of radioactive waste (RW) is most significant in the nuclear fuel cycle. In spite of its relatively low activity it is the major contributor to the formation of radiation hazards to the people and environment. The radioactivity of uranium ores and of their processing waste is due to natural radionuclides of uranium (238U and 235U) and thorium (232Th) radioactive decay chains.

Pre-Quaternary rocks and sediments with a high level of radioactivity in Denmark

The pre-Quaternary sediments and rocks in Denmark generally have a low content of radioactive minerals and elements. Uranium, thorium and radium are built into mineral structures or are, for example, adsorbed on the surface of clay minerals, Fe-minerals or organic material. Radon (222Rn) is a radioactive noble insoluble gas with a half-life of 3.8 days. It belongs to the uranium (238U) decay chain where radon is formed from radium (226Ra). When Rn is formed by radioactive decay from Ra, the emanation process sends part of the radon produced into the pore spaces of rocks and soils. From here, the radon can enter and accumulate in buildings. The source of the radioactive materials in Danish sediments and rocks is primarily from weathered Precambrian crystalline rocks from Norway, Sweden, Finland and the Danish island of Bornholm. Physical and chemical weathering disintegrates these rocks and rivers transport the material into the Danish–Norwegian and Danish–Polish sedimentary basins.

Mapping uranium concentration in soil: Belgian experience towards a European map

A map of uranium concentration in soil has been planned for the European Atlas of Natural Radiation. This Atlas is being developed by the Radioactivity Environmental Monitoring (REM) group of the Joint Research Centre (JRC) of the European Commission. The great interest in uranium compared to other terrestrial radionuclides stems from the fact that radon (222Rn) is in the decay chain of uranium (238U) and that public exposure to natural ionizing radiation is largely due to indoor radon.With several different databases available, including data (albeit not calibrated) from an airborne survey, Belgium is a favourable case for exploring the methodology of uranium mapping. A harmonized database of uranium in soil was built by merging radiological (not airborne) and geochemical data. Using this harmonized database it was possible to calibrate the data from the airborne survey.Several methods were used to perform spatial interpolation and to smooth the data: moving average without constraint, by soil class and by geological unit. When using the harmonized database, it is first necessary to evaluate the uranium concentration in areas without data or with an insufficient number of data points.Overall, there is a reasonable agreement between the maps on a 1 km × 1 km grid obtained with the two datasets (airborne U and harmonized soil U) with all the methods. The agreement is better when the maps are reduced to a 10 km × 10 km grid; the latter could be used for the European map of uranium concentration in soil.

A Study of Radioactive Contamination of Crystals for the AMoRE Experiment

A calcium molybdate ( $\text{CaMoO}_{4}$ ) crystal scintillator, with molybdenum enriched in $^{100}\text{Mo}$ and calcium depleted in $^{48}\text{Ca}$ ( $^{40}\text{Ca}{}^{100}\text{MoO}_{4}$ ), was developed by the Advanced Molybdenum based Rare process Experiment (AMoRE) collaboration to search for a neutrinoless double beta ( $0\nu \beta \beta $ ) decay of $^{100}\text{Mo}$ . We are planning to use about 10 kg of $^{40}\text{Ca}{}^{100}\text{MoO}_{4}$ crystals as cryogenic bolometers for the first phase of the experiment (AMoRE-I) at the Yang Yang underground laboratory (Y2L) in Korea. This experiment calls for an extremely low level of radioactive contamination in detectors, particularly by thorium, uranium, and radium decay chains. We measured scintillation properties and radioactive contamination of $\text{CaMoO}_{4}$ and $^{40}\text{Ca}{}^{100}\text{MoO}_{4}$ crystals at the Y2L. We also estimated the acceptable level of internal radioactive background using Monte Carlo simulation for the AMoRE-I.

Measurement of the total activity concentrations of Libyan oil scale

Twenty-three oil scale samples obtained from the Libyan oil and gas industry production facilities onshore have been measured using high-resolution gamma-ray spectrometry with a shielded HPGe detector, the work being carried out within the Environmental Radioactivity Laboratory at the University of Surrey. The main objectives of this work were to determine the extent to which the predominant radionuclides associated with the uranium and thorium natural decay chains were in secular equilibrium with their decay progeny, also to compare differences between the total activity concentrations (TAC) in secular equilibrium and disequilibrium and to evaluate the measured activities for the predominant gamma-ray emitting decay radionuclides within the 232Th and 238U chains. The oil scale NORM samples did not exhibit radioactive equilibrium between the decay progeny and longer-lived parent radionuclides of the 238U and 232Th series.

Mapping geogenic radon potential by regression kriging

Radon (222Rn) gas is produced in the radioactive decay chain of uranium (238U) which is an element that is naturally present in soils. Radon is transported mainly by diffusion and convection mechanisms through the soil depending mainly on the physical and meteorological parameters of the soil and can enter and accumulate in buildings. Health risks originating from indoor radon concentration can be attributed to natural factors and is characterized by geogenic radon potential (GRP). Identification of areas with high health risks require spatial modeling, that is, mapping of radon risk. In addition to geology and meteorology, physical soil properties play a significant role in the determination of GRP. In order to compile a reliable GRP map for a model area in Central-Hungary, spatial auxiliary information representing GRP forming environmental factors were taken into account to support the spatial inference of the locally measured GRP values. Since the number of measured sites was limited, efficient spatial prediction methodologies were searched for to construct a reliable map for a larger area. Regression kriging (RK) was applied for the interpolation using spatially exhaustive auxiliary data on soil, geology, topography, land use and climate. RK divides the spatial inference into two parts. Firstly, the deterministic component of the target variable is determined by a regression model. The residuals of the multiple linear regression analysis represent the spatially varying but dependent stochastic component, which are interpolated by kriging. The final map is the sum of the two component predictions. Overall accuracy of the map was tested by Leave-One-Out Cross-Validation. Furthermore the spatial reliability of the resultant map is also estimated by the calculation of the 90% prediction interval of the local prediction values. The applicability of the applied method as well as that of the map is discussed briefly.

Shielding concepts for low-background proportional counter arrays in surface laboratories

Development of ultra low background gas proportional counters has made the contribution from naturally occurring radioactive isotopes – primarily α and β activity in the uranium and thorium decay chains – inconsequential to instrumental sensitivity levels when measurements are performed in above ground surface laboratories. Simple lead shielding is enough to mitigate against gamma rays as gas proportional counters are already relatively insensitive to naturally occurring gamma radiation. The dominant background in these surface laboratory measurements using ultra low background gas proportional counters is due to cosmic ray generated muons, neutrons, and protons. Studies of measurements with ultra low background gas proportional counters in surface and underground laboratories as well as radiation transport Monte Carlo simulations suggest a preferred conceptual design to achieve the highest possible sensitivity from an array of low background gas proportional counters when operated in a surface laboratory. The basis for a low background gas proportional counter array and the preferred shielding configuration is reported, especially in relation to measurements of radioactive gases having low energy decays such as 37Ar.

NORM in the East Midlands' oil and gas producing region of the UK

Naturally occurring radioactive material (NORM) is a common feature in North Sea oil and gas production offshore but, to date, has been reported from only one production site onshore in the United Kingdom. The latter, Wytch Farm on the Dorset coast, revealed high activity concentrations of 210Pb in metallic form but little evidence of radium accumulation. NORM has now been discovered at two further onshore sites in the East Midlands region of the UK. The material has been characterized in terms of its mineralogy, bulk composition and disequilibrium in the natural uranium and thorium series decay chains. In contrast to Wytch Farm, scale and sludge samples from the East Midlands were found to contain elevated levels of radium and radioactive progeny associated with crystalline strontiobarite. The highest 226Ra and 228Ra activity concentrations found in scale samples were 132 and 60 Bq/g, with mean values of 86 and 40 Bq/g respectively; somewhat higher than the mean for the North Sea and well above national exemption levels for landfill disposal. The two East Midlands sites exhibited similar levels of radioactivity. Scanning electron microscope imaging shows the presence of tabular, idiomorphic and acicular strontiobarite crystals with elemental mapping confirming that barium and strontium are co-located throughout the scale. Bulk compositional data show a corresponding correlation between barium-strontium concentrations and radium activity. Scales and sludge were dated using the 226Ra/210Pb method giving mean ages of 2.2 and 3.7 years, respectively. The results demonstrate clearly that these NORM deposits, with significant radium activity, can form over a very short period of time. Although the production sites studied here are involved in conventional oil recovery, the findings have direct relevance should hydraulic fracturing for shale gas be pursued in the East Midlands oilfield.

Internal doses of French adult population linked to the intake of radionuclides from the decay-chains of uranium and thorium by foodstuffs ingestion

This study provides the first dose assessment to the French adult population due to the intake of radionuclides from the decay chains of uranium and thorium by foodstuff ingestion (water consumption excepted). This dose varies widely with the consumption of seafood, from less than 200 μSv.y-1 for people who do not consume shellfish or crustaceans at all, to more than 2,000 μSv.y-1 for the biggest consumers (about 150 kg.y-1 according to specific dietary surveys carried out along the French seaside). For moderate consumers of seafood (around 4.6 kg.y-1), who probably represent a major part of the population, this internal dose would be around 330 μSv.y-1. This variable consumption of seafood overshadows all the other causes of variability of these internal dose estimates.

The deportment of uranium decay chain radionuclides during processing of an Australian monazite concentrate using a caustic conversion route

Monazite is conventionally processed using caustic conversion and hydrochloric acid leaching in industry, to recover the rare earth elements (REE). Understanding the deportment of uranium decay chain radionuclides is of particular importance for product quality and occupational health and safety (OH&S) purposes. Here, the deportment of uranium decay chain radionuclides during the alkaline treatment route was investigated for the first time, using analytical techniques. Significant quantities of 226Ra, 210Pb and 227Ac were found to report to the rare earth chloride liquor. Subsequent impurity removal treatment generally resulted in the elimination of more than 85 % of radionuclides contained in the chloride liquor.

Investigation of the radiological impact on the coastal environment surrounding a fertilizer plant

This investigation was carried out in order to assess the marine environmental radioactive pollution and the radiological impact caused by a large production plant of phosphate fertilizer, located in the Lebanese coastal zone. Natural radionuclides (238U, 235U, 232Th, 226Ra, 210Po, 210Pb, 40K) and anthropogenic 137Cs were measured by alpha and gamma spectrometry in seawater, sediment, biota and coastal soil samples collected from the area impacted by this industry. The limited environmental monitoring program within 2 km of the plant indicates localized contamination with radionuclides of the uranium decay chain mainly due to the transport, the storage of raw materials and the free release of phosphogypsum waste.

The Earthʼs mantle and geoneutrinos

The KamLAND and Borexino experiments have observed, each at ∼4σ level, signals of electron antineutrinos produced in the decay chains of thorium and uranium in the Earthʼs crust and mantle (Th and U geoneutrinos). Various pieces of geochemical and geophysical information allow an estimation of the crustal geoneutrino flux components with relatively small uncertainties. The mantle component may then be inferred by subtracting the estimated crustal flux from the measured total flux. We find that crust-subtracted signals show hints of a residual mantle component, emerging at ∼2.4σ level by combining the KamLAND and Borexino data. The inferred mantle flux, slightly favoring scenarios with relatively high Th and U abundances, within ∼1σ uncertainties is comparable to the predictions from recent mantle models.

Measuring activity of 235, 238U, 232Th and 40K in geological materials using neutron activation analysis

The radioactivity of the 235, 238U and 232Th isotope decay chains for geological samples can usually be assumed to be in equilibrium due to their age. Similarly, one can assume that the isotopic mass proportions are equal to natural isotopic abundance. Current methods used to ascertain activity in these decay chains involve alpha particle spectrometry, ICP-MS or passive gamma-ray spectrometry, all of which can be laborious and time consuming. In this research, we have used thermal and epithermal neutron activation analysis (NAA) of small sample sizes of various geological materials in order to ascertain these activities. By using NAA, we aim to obviate cumbersome sample preparation, the need for large samples and extended counting time. In addition to the decay chains of uranium and thorium, 40K was also determined using epithermal neutron activation analysis to determine total potassium content and then subtracting out its isotopic contribution.

Mantle geoneutrinos in KamLAND and Borexino

The KamLAND and Borexino experiments have observed, each at ~4 sigma level, signals of electron antineutrinos produced in the decay chains of thorium and uranium in the Earth's crust and mantle (Th and U geoneutrinos). Various pieces of geochemical and geophysical information allow an estimation of the crustal geoneutrino flux components with relatively small uncertainties. The mantle component may then be inferred by subtracting the estimated crustal flux from the measured total flux. To this purpose, we analyze in detail the experimental Th and U geoneutrino event rates in KamLAND and Borexino, including neutrino oscillation effects. We estimate the crustal flux at the two detector sites, using state-of-the-art information about the Th and U distribution on global and local scales. We find that crust-subtracted signals show hints of a residual mantle component, emerging at ~2.4 sigma level by combining the KamLAND and Borexino data. The inferred mantle flux slightly favors scenarios with relatively high Th and U abundances, within +-1 sigma uncertainties comparable to the spread of predictions from recent mantle models.

Naturally occurring radionuclides in food and drinking water from a thorium-rich area

This paper focuses on a survey of uranium and thorium decay chain radionuclides in food and drinking water from the thorium-rich (monazite-bearing) region of Buena, which is located in the state of Rio de Janeiro, Brazil. The radionuclide concentration values in the food and drinking water from Buena reached values higher than 100-fold the international reference values. The daily intake of radionuclides by the local population is similar to that of another high background radiation area in Brazil, but the intake is higher than that of residents from a normal background radiation area. Approximately 58 % of the food consumed by Buena inhabitants is produced locally. Based on that figure, locally produced food and the dilution of total radionuclides in the diet of residents caused by food importation are both highly relevant to a population's intake of radionuclides. The concentration values for (210)Pb and the radium isotopes in drinking water from Buena are among the highest values to be reported in the literature. (228)Ra is the most important radionuclide ingested with both food and water among the inhabitants of Buena.

Estimation of the radiological background and dose assessment in areas with naturally occurring uranium geochemical anomalies—a case study in the Iberian Massif (Central Portugal)

Naturally occurring uranium geochemical anomalies, representative of the several thousand recognized in the Portuguese section of the Iberian Massif and outcropping in three target areas with a total of a few thousand square metres, were subjected to a detailed study (1:1000 scale) to evaluate the radiological health-risk on the basis of a dose assessment. To reach this goal some radioactive isotopes from the uranium, thorium and potassium radioactive series were measured in 52 samples taken from different environmental compartments: soils, stream sediments, water, foodstuff (vegetables) and air; external radiation was also measured through a square grid of 10×10m, with a total of 336 measurements. The results show that some radioisotopes have high activities in all the environmental compartments as well as a large variability, namely for those of the uranium decay chain, which is a common situation in the regional geological setting. Isotopic disequilibrium is also common and led to an enrichment of several isotopes in the different pathways, as is the case of 226Ra; maximum values of 1.76BqL−1 (water), 986Bqkg−1 (soils) and 18.9Bqkg−1 (in a turnip sample) were measured. On the basis of a realistic scenario combined with the experimental data, the effective dose from exposure to ionizing radiation for two groups of the population (rural and urban) was calculated; the effective dose is variable between 8.0 and 9.5mSvyear−1, which is 3–4 times higher than the world average. Thus, the radiological health-risk for these populations could be significant and the studied uranium anomalies must be taken into account in the assessment of the geochemical background. The estimated effective dose can also be used as typical of the background of the Beiras uranium metalogenetic province and therefore as a “benchmark” in the remediation of the old uranium mining sites.

Transfer of natural radionuclides from hay and silage to cow’s milk in the vicinity of a former uranium mine

After the closure of the former Žirovski Vrh uranium mine in Slovenia, mining and milling wastes were deposited on two waste piles, which are located close to the mine. These wastes contain elevated levels of natural radionuclides from the uranium decay chain. Due to different migration processes (erosion, aerial deposition, through groundwater), these radionuclides can be transported via fodder into cow’s milk, which is an important foodstuff for Slovenian people. Therefore, natural radionuclides were analysed in the transfer food chain from soil to cow’s fodder and cow’s milk. After sampling, 238U, 234U, 230Th, 226Ra, 210Pb and 210Po were determined using radiochemical separation methods and alpha spectrometry or proportional counting. Hay and silage to milk concentration ratios (kg dry weight L−1) were calculated and were 0.260 for 238U, 0.255 for 230Th, 0.070 for 226Ra, 0.021 for 210Pb and 0.019 for 210Po. The calculated annual ingestion dose due to milk consumption for the natural radionuclides analysed was 9 μSv/year for adults and 389 μSv/year for infants with the highest contribution of 210Po (51% for adults and 63% for infants) and 210Pb (36% for adults and 24% for infants). This study provides new data quantifying the transfer of natural radionuclides to milk, which is a parameter for which there have been very few previously reported values.

Radioactivity of dumps in mining areas of the Upper Silesian Coal Basin in Poland

Underground coal mining is associated with large quantities of gangue. In the past, the majority of gangue was not utilized but was placed in the vicinity of the coalmines forming cone-shaped dumps. Some of them contained even millions of tons of rock. Nowadays, environmental precautions extort larger utilization of any kind of waste materials, for example in road construction, civil engineering or as stowing in underground abandoned workings. Examination of the composition of waste dumps, including radioactivity, is thus an important issue. The paper presents results of a radiological survey carried out in several dumps located in the Upper Silesian Coal Basin in the south of Poland. Measurements of samples were carried out with the use of a gamma-ray spectrometer. Activity concentration results for the uranium and thorium decay chains are discussed.

Testing the potential of luminescence dating of high-alpine lake sediments

The potential of luminescence dating of high-alpine lacustrine sediments is tested on samples taken from three high-altitude moraine-bounded lakes in the Swiss Alps. Independent age control is provided by radiocarbon ages and detailed palynological data in all cases. All samples show good luminescence characteristics (no thermal transfer, good dose recovery and recycling), but two samples show rather low quartz signals. Radioactive disequilibria in the uranium decay chain observed in one sample are accounted for by using a dynamic modelling approach. Because all cores had largely dried out and water content had not been measured after sampling, we developed a modern limnological approach to retrospectively establish palaeo-water content. Applying average water content values from a dataset of modern sediments with similar characteristics to the samples investigated here we obtained ages that match the independent age control. Whereas the low-signal quartz separates consistently underestimate these ages, the polymineral samples more accurately match them, do not suffer from anomalous fading and are thus considered reliable. This study demonstrates for the first time that applying luminescence dating to high-alpine, ice-proximal lacustrine sediments is a promising avenue to obtain a chronology for such depositional environments.