Thorium Activity Research Articles

Measurements of Natural Radionuclides in Vegetables by Gamma Spectrometry

This article reports the activity of natural radionuclides uranium, thorium, and potassium, in different vegetables in Malaysia, measured with a p-type high-purity germanium detector (HPGe). Potassium radionuclides were the most prevalent element in the tested samples, whose activity ranges from 138.89 to 2660.31 Bq/kg. Meanwhile, the activity of uranium was found to be within the minimum detection limit (MDL) to 46.94 Bq/kg, and thorium from < MDL to 192.98 Bq/kg. The annual dose was in the range 0.001 to 0.06 mSv, within the worldwide range of 0.29 mSv/year for ingestion of vegetables.

Thorium isotopes (228Th, 230Th, 232Th) and applications in reconstructing the Yangtze and Yellow River floods

In the past decades, the floods of the Yangtze and Yellow River introduced unexpected changes of the ecological community and sedimentary dynamics in the East China Sea (ECS). To reconstruct the flood events in the ECS, 228Th, 230Th and 232Th have been examined in a sediment core. The specific activities of three thorium isotopes have good positive relations with fine fractions (<63 μm), indicating that Th activity concentrations heavily depend upon the sediment grain size. The size-normalized activities of 228Th, 230Th and 232Th showed significant variations. Coincidences between the higher Th activities and historical floods of the Yangtze and Yellow River demonstrated that size-normalized Th recorded the two rivers' flood events. The activity ratios of thorium isotopes, i.e. 230Th/232Th and 228Th/232Th, also showed similar patterns to the historical river floods. In three periods (1740s, 1840–1860s and 1930–1960s), characterized by frequent floods, the thorium activity ratios were fairly low and close to the Yangtze and Yellow River estuary sediments, coinciding with the less oceanic 228Th and 230Th contributions during the flooding periods. Accordingly, these results support the size-normalized Th activity and thorium ratios as proxies of the river floods in coastal seas.

Concentration and activity ratio of thorium isotopes in surface soil around proposed uranium mining site in India

Unconformity type of uranium deposits at Lambapur and Peddagattu located in Nalgonda District of Andhra Pradesh, India has been reported. Soil surveillance for isotopic thorium belonging to two different radioactive decay chains provide information on characterization of soil formation due to weathering of underlying host rocks. Thorium concentration and their isotopic activity ratio in localized soil samples were assessed. Thorium concentration and 230 Th/ 232 Th activity ratio were observed to be in the range of 15 ± 3 mg/kg to 132 ± 15 mg/kg and 0.21 ± 0.07-0.68 ± 0.05, respectively. A significant wide variation in thorium concentration and that of activity ratio for localized area soil indicates the soil development due to a different type of underlying host rocks. Activity ratio of 228 Th/ 232 Th in the soil samples of the study area are observed to vary from 0.87 ± 0.05 to 1.07 ± 0.15 with a mean of 0.96 ± 0.02, indicating secular equilibrium between 232 Th and its daughter product 228 Th. The study describes the application of isotopic thorium activity as a chronological indicator for geological characterization.

Comparative study of different analytical methods for the determination of 238U, 234U, 235U, 230Th and 232Th in NORM samples (Southern Catalonia)

Uranium and thorium isotopes from sludge samples taken from an area of influence of a dicalcium phosphate factory, located close to the Ebro River reservoir in Flix, and from mineral raw materials (coal and phosphate) which were deposited in Tarragona Harbour (Catalonia) have been measured. To do that, several procedures to determine these isotopes have been applied and compared in terms of accuracy, precision and total analysis time. In particular, digestion procedures, such as one based on conventional acidic digestion or another based on the use of microwave digestion, have been tested. Moreover, different radiochemical separation procedures have been applied. In this regard, one method based on liquid–liquid extraction using TBP/Xylene and another based on the use of extraction chromatography using UTEVA resins have been compared. Firstly, the different proposed methods were tested by analyzing a phosphogypsum sediment and a moss-soil sample from two different intercomparison exercises. The microwave digestion – UTEVA method provided the best results (recoveries higher than 82% for uranium and thorium isotopes) and was then applied to the NORM samples. The obtained results showed that the higher uranium and thorium activities values were found in phosphate raw material and in the more superficial samples located in sludge sediments next to the dicalcium phosphate factory.

How does dynamical spatial variability impact 234Th-derived estimates of organic export?

In this study we first evaluate the small-scale spatial variability of particulate export, using a set of synoptic thorium-234 activity observations sampled within a one-degree radius. These data show significant variability of surface thorium activity on scales of the order of 100km (∼270–550dpmm−3). This patchiness of export potentially affects the robustness of point observations and our interpretation of them. Motivated by these observations we subsequently couple an explicit model of thorium-234 dynamics to a coupled physical–biogeochemical basin model capable of resolving these small-scales. The model supports the observations in displaying marked thorium variability on spatial scales of the order of 100km and smaller, with highest values in the regions of large eddy kinetic energy and large primary productivity. The model is also used to quantify the impact of small-scale variability on export estimates. Our model shows that the primary source of error associated with the presence of small-scale spatial variability is related to the standard assumptions of steady state and non-steady state (>40% during bloom condition). The non-steady state method can misinterpret variations due to patchiness in thorium activity as temporal changes and lead to errors larger than those introduced by the simpler steady state approach. We show that the non-steady state approach could improve the flux estimates in some cases if the sampling was conducted in a Lagrangian framework. Undersampling the spatial variability results in further bias (>20%) that can be reduced when the sampling density is increased. Finally, errors due to the dynamical transport of thorium associated with small-scale structures are relatively low (<20%) except in regions of high eddy kinetic energy.

Estimation of Low-Level Radiation Dose from Some Building Materials Using Gamma Spectroscopy

The study of the radiation hazards from building materials is of interest in many countries. So, it becomes necessary to study the natural radioactivity in different materials to assess the dose for the population to know the health risks and to have a baseline for future changes in the environmental radioactivity due to human activities. The present study assesses the level of terrestrial gamma radiation and associated dose rates from the naturally occurring radionuclides 226Ra, 232Th and 40K in building materials collected from the Northeastern part of Haryana state of India using gamma ray spectrometry. Places are in the vicinity of Shivalik range of Himalayas. The activity of radium, thorium and potassium in various soil samples varied from 27 ± 1.2 to 51 ± 1.5 Bq/kg, 42 ± 1.5 to77 ± 2.3 Bq/kg and 277 ± 3.2 to 584 ± 6.1 Bq/kg and in various building materials varied from 14 ± 0.4 to 87 ± 7.7 Bq/kg, 6 ± 0.3 to 24 ± 1.1 Bq/kg and 26 ± 0.4 to 245 ± 3.7 Bq/kg, respectively. The values of absorbed annual effective doses (indoors and outdoors) were found to vary in various soil samples from 50 to 95 nGyh−1, 0.24 to 0.46 mSv and 0.06 to 0.12 mSv and in various building materials found to vary from 11 to 57 nGyh−1, 0.05 to 0.28 mSv and 0.01 to 0.07 mSv, respectively.

Synthesis, structural studies and biological activity of dioxomolybdenum(VI), dioxotungsten(VI), thorium(IV) and dioxouranium(VI) complexes with 2-hydroxy-5-methyl and 2-hydroxy-5-chloroacetophenone benzoylhydrazone

New complexes of MoO2(VI), WO2(VI), Th(IV) and UO2(VI) with aroyl hydrazones have been prepared and characterized by various physicochemical methods. Elemental analysis suggested 1 : 1 metal : ligand stoichiometry for MoO2(VI), WO2(VI), and UO2(VI) complexes whereas 1 : 2 for Th(VI) complexes. The physicochemical studies showed that MoO2(VI), Th(IV) and UO2(VI) complexes are octahedral. The electrical conductivity of these complexes lies in the range 1.00 × 10−7−3.37 × 10−11Ω−1 cm−1 at 373 K. The complexes were found to be quite stable and decomposition of the complexes ended with respective metal oxide as a final product. The thermal dehydration and decomposition of these complexes were studied kinetically using both Coats-Redfern and Horowitz-Metzger methods. It was found that the thermal decomposition of the complexes follow first order kinetics. The thermodynamic parameters of the decomposition are also reported. The biological activities of ligands and their metal complexes were tested against various microorganisms.

Variation of 231Pa, 230Th and 231Paex/230Thex in surface sediments of the Sabah–Sarawak coastal waters

Protactinium and thorium activities were measured in eight surface sediment taken in 2004 to determine effectiveness scavenging of 231Pa at Sabah–Sarawak coastal waters. The result found that activity ratios of 231Paex/230Thex were ranged from 0.07 to 0.13 at all sampling stations. The high 231Paex/230Thex activity ratio than the production ratio of 0.093 in seawater at station SR 01, SR 02, SR 04, SB 02 and SB 05, revealed that 231Pa is effectively removed from the water column into the sediment in comparison with 230Th at those stations. Low percentage of 230Thex (90–95%) in comparison with 231Paex at all stations can be attributed to less efficiently scavenged of 230Th onto particles prior deposited at the marine sediment bed.

A comparative study of thorium activity in NORM and high background radiation area

Several industrial processes are known to enrich naturally occurring radioactive materials (NORM). To assess such processes with respect to their radiological relevance, characteristic parameters describing this enrichment will lead to interesting information useful to UNSCEAR. In case of mineral treatment plants, the high temperatures used in smelting and refining processes lead to high concentrations of (238)U and (232)Th. Also due to thermal power combustion, concentration of U and Th in the fly ash increases manifold. NORM samples were collected from a Thailand mineral treatment plant and Philippine coal-fired thermal power plants for investigation. Some studies are initiated from a high background radiation area near Gopalpur of Orissa state in India. These NORM samples were analysed by gamma-ray spectrometry as well as inductively coupled plasma mass spectrometry. The radioactivity in case of Orissa soil samples is found to be mainly contributed from thorium. This study attempts to evaluate levels of thorium activity in NORM samples.

Radioactivity distribution of thorium in sediment core of the Sabah-Sarawak coast

Thorium activity concentrations were measured in seven marine sediment cores taken from Sabah-Sarawak coast on 2004 by using a gravity box corer. Collected sediments were generally homogenous mud which contained much more mixture of silt and clay compared to sand and relatively low content of organic carbon (i.e. less than 5% at all sampling stations). The results found that activity concentrations of 230Th, 232Th and ratios of 230Th/232Th were ranged from 6.5–20.4 Bq/kg dry wt., 6.8–27.8 Bq/kg dry wt. and 0.69–0.92, respectively. It seem that, 232Th activity concentrations are slightly higher than 230Th at all sampling stations and both radionuclides were generally high at Sabah compared to Sarawak coastal waters. 230Th activity concentrations in sediment core appear to be correlated with the activity concentrations of 232Th at some sampling station. These indicating both radionuclides were supplied from the same of environment and source origin of detrital from terrestrial and shallower water. The low 230Th/232Th activity ratio which is less than unity suggesting that 232Th was actively and rapidly regenerated compared to 230Th from 234U. It also can be attributed to less efficiently scavenge of 230Th onto particles prior deposited at the marine sediment bed.

Measuring 226Ra and 232Th activity in soil and vegetation samples using a method of double γ-coincidences

A coincidence method for measuring radium and thorium activity has been developed using the PRIPYAT-2M gamma-ray coincidence spectrometer, with six NaI(Tl) detectors and registration geometry close to 4π. It was tested by measuring soil samples from the Northern region of Montenegro, as well as vegetation samples from the same region. The results showed a good agreement with ones obtained by the HPGe spectrometer.

EVALUATION OF TOTAL EFFECTIVE DOSE DUE TO CERTAIN ENVIRONMENTALLY PLACED NATURALLY OCCURRING RADIOACTIVE MATERIALS USING A PROCEDURAL ADAPTATION OF RESRAD CODE

Due to a recent upward trend in the price of uranium and subsequent increased interest in uranium mining, accurate modeling of baseline dose from environmental sources of radioactivity is of increasing interest. Residual radioactivity model and code (RESRAD) is a program used to model environmental movement and calculate the dose due to the inhalation, ingestion, and exposure to radioactive materials following a placement. This paper presents a novel use of RESRAD for the calculation of dose from non-enhanced, or ancient, naturally occurring radioactive material (NORM). In order to use RESRAD to calculate the total effective dose (TED) due to ancient NORM, a procedural adaptation was developed to negate the effects of time progressive distribution of radioactive materials. A dose due to United States' average concentrations of uranium, actinium, and thorium series radionuclides was then calculated. For adults exposed in a residential setting and assumed to eat significant amounts of food grown in NORM concentrated areas, the annual dose due to national average NORM concentrations was 0.935 mSv y(-1). A set of environmental dose factors were calculated for simple estimation of dose from uranium, thorium, and actinium series radionuclides for various age groups and exposure scenarios as a function of elemental uranium and thorium activity concentrations in groundwater and soil. The values of these factors for uranium were lowest for an adult exposed in an industrial setting: 0.00476 microSv kg Bq(-1) y(-1) for soil and 0.00596 microSv m(3) Bq(-1) y(-1) for water (assuming a 1:1 234U:238U activity ratio in water). The uranium factors were highest for infants exposed in a residential setting and assumed to ingest food grown onsite: 34.8 microSv kg Bq(-1) y(-1) in soil and 13.0 microSv m(3) Bq(-1) y(-1) in water.

Uranium and thorium in soils, mineral sands, water and food samples in a tin mining area in Nigeria with elevated activity

The activity concentrations of uranium and thorium have been determined in soils and mineral sands from the Nigerian tin mining area of Bisichi, located in the Jos Plateau, and from two control areas in Nigeria (Jos City and Akure) using high-purity germanium detectors (HPGe). High resolution sector field inductively coupled plasma mass spectroscopy (HR-SF-ICP-MS) was used to determine uranium and thorium in liquids and foodstuffs consumed locally in the mining area. The activities of uranium and thorium measured in the soils and mineral sands from Bisichi ranged from 8.7 kBq kg −1 to 51 kBq kg −1 for 238U and from 16.8 kBq kg −1 to 98 kBq kg −1 for 232Th, respectively. These values were significantly higher than those in the control areas of Jos City and Akure and than the reference values reported in the literature. They even exceeded the concentrations reported for areas of high natural radioactive background. Radionuclide concentrations in samples of the local foodstuffs and in water samples collected in Bisichi were found to be higher than UNSCEAR reference values. The results reveal the pollution potential of the mining activities on the surrounding areas.

Detection efficiencies of 226Ra and 232Th in different modes of counting of the PRIPYAT-2M spectrometer

Detection efficiencies of 226Ra and 232Th decay products, as well as corresponding minimum detectable activities in different modes of counting of the PRIPYAT-2M spectrometer (integral, when all pulses - coincident and non-coincident, are counted; non-coincident, when only non-coincident pulses are counted; coincident, when coincident pulses of multiplicity from 2 to 6 are counted), in energy ranges of 200 keV to 2000 keV and 300 keV to 3000 keV are presented here. It has been shown that the mode of double coincidences is the optimum one for measuring radium and thorium activity. In this mode of counting, the sensitivity of the spectrometer is the highest.

Measuring the activity of thorium by its decay products using a multidetector γ-ray coincidence spectrometer

A method for detecting thorium by its decay products has been tested on PRIPYAT six-crystal 4π γ-ray coincidence spectrometers. This method makes it possible to measure large-volume samples of any shape with a higher sensitivity and a shorter acquisition time than when an HPGe spectrometer with a comparable cost is used.

Determination of uranium, thorium and potassium activity concentrations in soil cores in Araba Valley, Jordan

Determination of uranium, thorium and potassium activity concentrations in soil cores in Araba Valley, Jordan

Measurement of natural radioactivity and radon exhalation rate from rock samples of Jaduguda uranium mines and its radiological implications

The Singhbhum shear zone is a 200km long arcuate belt in Jharkhand state situated in eastern India. The central part between Jaduguda–Bhatin–Nimdih, Narwapahr–Garadih–Turamdih is rich in uranium. Presence of uranium in the host rocks and the prevalence of a confined atmosphere within mines could result in enhanced concentration of radon (222Rn) gas and its progeny. Inhalation of radon daughter products is a major contributor to the radiation dose to exposed subjects. By using high resolution γ-ray spectroscopic system various radionuclides in the rock samples, collected from different places of Jaduguda uranium mines have been identified quantitatively based on the characteristic spectral peaks. The activity concentrations of the natural radionuclides, uranium (238U), thorium (232Th) and potassium (40K) were measured in the rock samples and radiological parameters were calculated. Uranium concentration was found to vary from 123±7Bqkg−1 to 40,858±174Bqkg−1. Activity of thorium was not significant in the samples, whereas, few samples have shown potassium activity from 162±11Bqkg−1 to 9024±189Bqkg−1. Radon exhalation rates from these samples were also measured using “Sealed Can technique” and found to vary from 4.2±0.05 to 13.7±0.08 Bq m−2h−1. A positive correlation was found between the radon exhalation rate and the uranium activity. The absorbed dose rates vary from 63.6 to 18876.4nGyh−1, with an average value of 7054.2nGyh−1. The annual external effective dose rates vary from 0.7 to 23.2mSvy−1. Radium equivalent activities (Raeq) varied from 134.3 to 40858.0Bqkg−1. Value of external hazard index (Hex) varied from 0.4 to 110.4 with an average value of 41.2.

A comparison of alpha and gamma spectrometry for environmental natural radioactivity surveys

An α-spectrometry, using automated borate fusion and sequential extraction and exchange chromatography, was used to determine the uranium and thorium based on environmental radioactivity of 20 soil samples. The same set of the samples was analysed using γ-spectrometry with an HPGe detector. The two data sets were checked for coherence using Z-score and χ 2 statistical tests. We show that γ-spectrometry is a valid alternative to time-consuming α-spectrometry for the determination of natural uranium and thorium activity in soil (activity range: 12.5–58.2 Bq/kg). The measured activities were compared with the theoretical activities to ensure secular equilibrium in the 238U and 232Th series. For 226Ra, a special study was made on deconvolution of the 186 keV multiplet with the Levenberg–Marquardt algorithm. Finally, the combined use of Z-score and χ 2-tests was found to be a powerful tool for comparing the results obtained with two different methods.

Investigation of uranium and thorium activities and their isotopic ratios in environmental water samples in Tokushima, Japan, using extraction chromatography and samarium coprecipitation

A highly sensitive separation procedure has been developed to investigate uranium and thorium activities and their isotopic ratios in environmental water samples in Tokushima, Japan. Uranium and thorium isotopes in environmental water samples were simultaneously isolated from interfering elements with extraction chromatography using an Eichrom UTEVA™ resin column. After the chemical separation, activities of U and Th isotopes coprecipitated with samarium fluoride (SmF3) were measured by α-spectrometry. It has been confirmed that uranium isotopes are isolated successfully from thorium decay chains by analyzing a test aqueous solution as a simulation of an environmental water sample. The separation procedure has been first applicable to the determination of U and Th activities and their isotopic ratios in a drinking well water named “Kurashimizu” in Tokushima City, Japan. The specific activities of 238U and 232Th in “Kurashimizu” were deduced to be within the upper limits of <0.31 and <0.19 mBq/l, respectively.

Constraining initial 230Th activity in incrementally deposited, biogenic aragonite from the Bahamas

The 230Th content of subsurface Bahamas seawater has been estimated from incrementally deposited aragonite skeletons of sclerosponges using U-series age models which imply syndepositional incorporation of 230Th. First order age models, assuming constant growth rate and zero initial 230Th activity, display an average surface age of 63 ± 18 y despite the fact that the surfaces of the organisms were known to be alive at the time collection in the 1990s. A knowledge of the initial 230Th activity is necessary to incorporate the surface age constraint into an age model. In the Bahamas, this approach estimates an initial 230Th/ 232Th activity ratio of 4.3 ± 1.1 when applied to several individuals of the Caribbean sclerosponge Ceratoporella nicholsoni. These results differ from the same approach applied to previous work on Jamaican sclerosponges accreting aragonite in an environment closer to crustal sources and with less carbonate substrate. We report new measurements of Jamaican sclerosponge suggesting initial activity ratios of 230Th/ 232Th of ∼1, albeit with a high amount of uncertainty, indicating a regional difference in initial thorium activities. The estimates of initial 230Th/ 232Th activity ratios in the Bahamas are similar to the dissolved ratio rather than the particulate ratio and can be explained by mixing of open ocean water and bank-top surface water, however no information regarding temporal changes in the amount of initial 230Th/ 232Th activity available for incorporation into biogenic aragonite can be constrained using this approach. Growth rates do not change after correction for initial thorium and they display an inverse relationship with depth. Although this paper deals uniquely with sclerosponge aragonite, it is likely that the approach can be used on any incrementally deposited biogenic aragonite, provided information is known a priori about the first order growth model and there is evidence that initial thorium incorporation is representative of ambient environment rather than individual physiology.