Chemical characterization of graphite by instrumental neutron activation analysis

Nuclear and commercial grade graphite samples were analysed by instrumental neutron activation analysis (INAA) using high flux reactor neutrons. Eleven elements (Na, K, As, Sc, Fe, Cr, Co, Zn, La, Ce, and Sm) were determined in eight samples of graphite (two nuclear grade and six commercial grade) by irradiating at a neutron flux of 3?×?10¹³ cm^?2 s^?1 in CIRUS reactor and assaying the activity by high-resolution gamma ray spectrometry using 40% relative efficiency HPGe detector coupled to an MCA. Concentrations of elements were determined by relative method of INAA. Results of both types of graphites as well as detection limits achieved by INAA method are discussed in the paper.     

Estimation of thorium intake due to consumption of vegetables by inhabitants of high background radiation area by INAA

A study was conducted to estimate the thorium concentration in locally grown vegetables in high background radiation area (HBRA) of southern coastal regions of India. Locally grown vegetables were collected from HBRA of southern coastal regions of India. Thorium concentration was quantified using instrumental neutron activation analysis. The samples were irradiated at CIRUS reactor and counted using a 40% relative efficiency HPGe detector coupled to MCA. The annual intake of thorium was evaluated using the consumption data provided by National Nutrition Monitoring Board. The daily intake of ²³²Th from the four food categories (green leafy vegetables, others vegetables, roots and tubers, and fruits) ranged between 0.27 and 5.352?mBq?d^?1. The annual internal dose due to ingestion of thorium from these food categories was 46.8?×?10^?8 for female and 58.6?×?10^?8?Sv?y^?1 for male.     

Determination of trace concentrations of thorium in uranium oxide matrix by epithermal instrumental neutron activation analysis

An epithermal instrumental neutron activation analysis (EINAA) method using cadmium filter was standardized to determine trace concentrations of thorium in four samples of uranium oxide (U₃O₈) samples. Samples and thorium standards, wrapped with cadmium foil, were irradiated at a reactor neutron flux of about 10¹² cm^?2 s^?1. Radioactive assay was carried out using a Compton suppressed anticoincidence gamma ray spectrometer consisting of HPGe-BGO detectors coupled to MCA. Concentrations of thorium in these samples were found to be in the range of 15–72 mg kg^?1. EINAA results were validated by determining thorium concentrations in uranium matrix by standard addition method. EINAA results were compared with those obtained by two wet chemical methods namely ion chromatography (IC) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results obtained by the three methods were found to be in good agreement, indicating further validity of the proposed EINAA method.     

Determination of concentrations of U and Th in their mixed oxides by INAA methods

Uranium and thorium mixed oxides are being prepared using natural U and Th for studies on fuels for Advanced Heavy Water Reactors, wherein composition of U and Th is specific and requires strict control in terms their contents and homogeneity. Chemical quality control necessitates accurate and precise compositional characterization of the fuel material by a suitable analytical method. Among various analytical methods for U and Th, instrumental neutron activation analysis (INAA) is one of the best methods for their simultaneous determination without chemical dissolution and separation. INAA methods using reactor neutrons namely thermal NAA and epithermal NAA were standardized for the determination of U and Th in their mixed oxides. Standards, synthetic samples and U–Th mixed oxide samples, prepared in cellulose matrix, were irradiated at pneumatic carrier facility of Dhruva reactor as well as at self serve facility of CIRUS reactor under cadmium cover (0.5 mm). Radioactive assay was carried out using a 40% relative efficiency HPGe detector. Both activation and daughter products of ²³⁸U (²³⁹U and ²³⁹Np) and ²³²Th (²³³Th and ²³³Pa) were used for their concentration determination. The method was validated by analyzing synthetic samples of 6–48%U–Th mixed oxides. The standardized method was used for the concentration determination of U and Th in 4–30%U–Th mixed oxide samples. Results of U and Th concentrations including associated uncertainties obtained from the INAA methods are presented in this paper.     

Application of INAA for phyto-accumulation study of selenium by chickpea plant

The phyto-accumulation efficacy of selenium (Se) from soil by chickpea plant is reported. Chickpea plants were grown in soil having different concentrations (1–4 mg kg^?1) of Se. Samples of soil and different parts of chickpea plants in Se rich soil were analyzed for determination of Se concentrations by instrumental neutron activation analysis (INAA). Samples were irradiated in self-serve facility of CIRUS reactor, BARC, Mumbai at a neutron flux of the order of 10¹³ cm^?2 s^?1. The gamma activity at 264.7 keV of ⁷⁵Se (119.8 d) was measured using a 45% relative efficiency HPGe detector coupled to MCA. Dependence of Se distribution in soil and plants on its spiking concentration was evaluated in this work. The Se concentrations determined in plant parts grown in control soil and in soil spiked with Se (4 mg kg^?1) are in the range of 0.6–0.8 and 65–68 mg kg^?1 respectively.     

Determination of aluminium contents in selected food samples by instrumental neutron activation analysis

Food and food products are the main sources of Aluminium entering the human body. In order to know aluminium contents in food and food products, selected 26 samples from local market were analyzed by instrumental neutron activation analysis (INAA) using reactor neutrons and high resolution gamma-ray spectrometry. INAA using 1,779 keV γ-ray of ²⁸Al (2.24 min) was used for aluminium concentrations in the range of 33–529 mg kg^?1. Two NIST standard reference materials (SRMs) and two IAEA reference materials (RMs) were analyzed by INAA for quantification of aluminium as a part of method validation.     

Effect of the natural radioactivity concentrations and 226Ra/238U disequilibrium on cancer diseases in Penang,Malaysia

Natural radioactivity measurements and assessment of radiological hazards in soil and sand samples obtained from Penang, Malaysia were carried out using the Exploranium GR-135 Plus “Identifier” Radioisotope Identification Device and high-resolution High Purity Germanium (HPGe) detector system. The activity concentrations of ²³⁸U, ²²⁶Ra, ²³²Th, and ⁴⁰K were found to be 184±11, 396±22, 165±14, and 835±28 Bq kg^?1 respectively, and the external gamma dose rate is 315±44 nGy h^?1 for soil samples. For sand samples, the activity concentrations of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K were 31±8, 62±16, 36±6, and 369±17 Bq kg^?1, respectively, and the external gamma dose rate is 66±12 nGy h^?1. To assess the radiological hazard of radioactivity present in the samples, the radium equivalent activity, annual effective dose, annual gonadal dose equivalent, external hazard, and internal indices were calculated.The Ra_eq values of soil samples were higher than the limit of 370 Bq kg^?1, which is equivalent to a gamma dose of 1.5 mSv yr^?1, whereas the Ra_eq for sand samples was lower than 370 Bq kg^?1. The calculated concentrations by HPGe spectroscopy were compared with the measured concentrations detected by a GR-135 spectrometer. The calculated and measured gamma dose rates had an ideal correlation coefficient R of 0.72. The gamma dose rates in Penang increased with the average annual age-standardized rates (ASR) for all cancers between 1994 and 2010. The effects of the pH value of soil and sand samples on natural radionuclides concentrations were investigated. The high concentration of ²²⁶Ra/²³⁸U ratio disequilibrium (²²⁶Ra/²³⁸U of 1.76–2.33) was observed in the sampling sites. Moreover, a portable continuous radon monitor (SNC, model 1029, Sun Nuclear Corporation) was used to measure the radon concentration of the soil surface. The radon concentrations were found to vary from 7 to 50 Bq m^?3. A positive correlation was observed between the radon and radium concentrations in samples measured by the SNC continuous radon monitor and HPGe detector.     

High precision elemental abundances for tektites and crater glasses-thorium,uranium and potassium

Thorium, uranium and potassium mean abundances for 15 Ivory Coast tektites, 23 Australites, 10 Philippinites, 25 Thailandites, 16 Bediasites and 12 Moldavites are reported. Abundances are also reported for Muong Nong type tektites, Nordlinger Ries crater glass, Bosumtwi crater glass and Darwin crater glass. Previous measurements are reviewed. The value of the present work lies in the fact that high precision instrumental neutron activation analysis was employed to measure a large number of tektites encompassing the major strewn fields. Four independent measurements of thorium were made for each specimen with two Ge(Li) gamma spectrometers. Two of the measurements were based on the 312 keV gamma of²³³Pa, while the other two measurements were based on the uranium and X-rays which accompany the decay of²³³Pa. Internal consistency among the four thorium measurements is high. The uranium measurements were based on the 106 keV gamma of²³⁹Np, while potassium was measured from the 1524 keV gamma of⁴²K.     

Investigation of radioactive lead,uranium, and thorium in environmental waters by extraction chromatography resins

A time-saving and sensitive method for monitoring low concentration (activities) of ²¹⁰Pb, ²³²Th, and ²³⁰Th and ²³⁸U, ²³⁴U, and ²³⁵U in water samples has been developed. Through the combination of co-precipitation and extraction chromatography by 3M RAD disks and UTEVA (Eichrom) columns effective radiochemical separation of the analytes was carried out. Thorium and uranium activities were determined by alpha spectrometry and lead activity by LSC, respectively. The minimal detectable activities obtained were 0.6?Bq?m^?3 for uranium, 0.29?Bq?m^?3 for thorium, and 2.5?Bq?m^?3 for ²¹⁰Pb. More than 150 different waters were analysed for uranium content and only 30 for lead and thorium. The investigations are still in progress.     

Thorium determination in a liver autopsy sample via direct γ-spectrometry and neutron activation analysis

Thorium was determined in a liver autopsy sample from a person treated with Thorotrast ca. 40 y earlier. The decay products²²⁸Ac,²²⁴Ra,²¹²Pb,²¹²Bi, and²⁰⁸Tl from the²³²Th series were identified by direct -spectrometry. Instrumental neutron activation analysis yielded a value of ca 22 g thorium per kg dry liver material. The total radiation dose to the whole liver was estimated in the order of 16 Gy.     

Study of arsenic (As) mobilization in the Ganga Alluvial Plain using neutron activation analysis

In northern part of Indian sub-continent, As related environmental and health issues receive attention from all over the world. Forty-eight sediment samples were collected from the Ganga Alluvial Plain (GAP) and its weathering products (from the Gomati River) for the study of As distribution and mobilization. These sediment samples were analyzed by Instrumental Neutron Activation Analysis (INAA) method using Cirus Research Reacter of Bhabha Atomic Research Centre, Mumbai. Average As concentrations in the GAP sediments (10.44?mg?kg^?1), the Gomati River bed sediments (1.36?mg?kg^?1) and the Gomati River suspended sediments (5.30?mg?kg^?1) were reported. Significant decrease of As content from the alluvial sediments to the river sediments is a clear indication of its mobilization by chemical weathering processes of mineral biotite. Present study demonstrates the importance of INAA for quantification and mobilization of As and improves our understanding related to As related environmental issues in northern India and elsewhere.     

A neutron activation analysis procedure for the determination of uranium,thorium and potassium in geologic samples

A neutron activation analysis procedure was developed for the determination of uranium, thorium and potassium in basic and ultrabasic rocks. The three elements are determined in the same 0.5-g sample following a 30-min irradiation in a thermal neutron flux of 2·10¹² n·cm^?2·sec^?1. Following radiochemical separation, the nuclides²³⁹U (T=23.5 m),²³³Th (T=22.2 m) and⁴²K (T=12.36 h) are measured by β-counting. A computer program is used to resolve the decay curves which are complex owing to contamination and the growth of daughter activities. The method was used to determine uranium, throium and potassium in the U. S. Geological Survey standard rocks DTS-1, PCC-1 and BCR-1. For 0.5-g samples the limits of detection for uranium, throium and potassium are 0.7, 1.0 and 10 ppb, respectively.     

Distribution of thorium in soils surrounding the rare-earth tailings reservoir in Baotou,China

Thorium distribution was investigated in the soils surrounding the rare-earth (RE) tailings reservoir near the Baotou grassland of Inner Mongolia, northern China. Totally 77 soil samples were collected from 8 different directions in the periphery of the RE tailings reservoir, and then were determined for ²³²Th. The ²³²Th activity degree ranges from 9.1 to 307.1 Bq kg^?1 with an average value of 42.4 Bq kg^?1. In some samples, the degree is higher than that of global average, showing that these soils were polluted by thorium. There is a high linear correlation coefficient between the thorium diffusion coefficient parameter and the wind intensity parameter which indicates that the distribution of ²³²Th is mainly correlated with wind speed and direction. The geo-accumulation index method was used to evaluate the level of thorium pollution, and the Kriging method was applied to estimate the land area at each level. By calculation, result shows that the area at each pollution level is 2.10 km² with medium-strong pollution, 38.29 km² with medium pollution, and 47.19 km² with slight pollution. The remaining 738.63 km² of land investigated is clear from thorium pollution.     

Determination of thorium and uranium at the nanogram per gram level in semiconductor potting plastics by neutron activation analysis

A method was developed to determine thorium and uranium in semiconductor potting plastics. The method is based on neutron activation and subsequent radiochemical separation to isolate and permit measurement of the daughter products²³³Pa and²³⁹Np of the induced²³³Th and²³⁹U. These plastics typically contain macro amounts of silicon, bromine and antimony and nanogram per gram amounts of thorium and uranium. The radiochemical method provides the necessary sensitivity and makes it possible to easily attain adequate decontamination of the tiny amounts of²³³Pa and²³⁹Np from the high levels of radioactive bromine and antimony.Deceased     

Determination of uranium and thorium at the sub-ng/g-level in high-purity aluminium by radiochemical neutron activation analysis

Summary A radiochemical neutron activation analysis technique for the determination of uranium und thorium in highpurity aluminium via the indicator radionuclides ²³⁹Np and ²³³Pa, respectively, has been developed. The separation procedure is based on the removal of ²⁴Na on hydrated antimony pentoxide followed by ion-exchange on Dowex-1X8 from HCl/HF and HCl medium. The eluate fraction being of interest for the determination of uranium and thorium contains > 99% of ²³⁹Np and ²³³Pa and, in addition, 11±2% of hafnium and 29±5% of zirconium, and non-detectable fractions of other radionuclides. For a 3-day irradiation of a 100 mg sample at a thermal neutron flux of 10¹⁴cm^–2s^–1 and a decay time of 5 days, the attainable detection limit for both elements is 0.05 ng/g. The method was applied to the analysis of different high-purity aluminium samples, and the results are compared with those obtained in other laboratories.

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Bestimmung von Uran und Thorium in hochreinem Aluminium im sub-ng/g-Bereich durch radiochemische Neutronenaktivierungsanalyse

     

Energy dispersive X-Ray fluorescence determination of thorium in phosphoric acid solutions

Energy dispersive X-ray fluorescence studies on determination of thorium (in the range of 7 to 137 mg/mL) in phosphoric acid solutions obtained by dissolution of thoria in autoclave were made. Fixed amounts of Y internal standard solutions, after dilution with equal amount of phosphoric acid, were added to the calibration as well as sample solutions. Solution aliquots of approximately 2–5 µL were deposited on thick absorbent sheets to absorb the solutions and the sheets were presented for energy dispersive X-ray fluorescence measurements. A calibration plot was made between intensity ratios (Th Lα/Y Kα) against respective amounts of thorium in the calibration solutions. Thorium amounts in phosphoric acid samples were determined using their energy dispersive X-ray fluorescence spectra and the above calibration plot. The energy dispersive X-ray fluorescence results, thus obtained, were compared with the corresponding gamma ray spectrometry results and were found to be within average deviation of 2.6% from the respective gamma ray spectrometry values. The average precision obtained in energy dispersive X-ray fluorescence determinations was found to be 4% (1σ). The energy dispersive X-ray fluorescence method has an advantage over gamma ray spectrometry for thorium determination as the amount of sample required and measurement time is far less compared to that required in gamma ray spectrometry.     

Spatial evaluation of radionuclide concentrations and the associated radiation hazards using the Kriging method

Spatial variations of natural and artificial radiation hazards are evaluated by combining high-resolution gamma spectrometry with the Kriging method. The coupling of both methods was applied on radionuclides’ concentration measurements of northern Jordan soil, and the generated smooth surfaces had mean standardized error and root mean square standardized error values ranging from 6?×?10^?3 to 26?×?10^?3 and from 0.89 to 1.19, respectively. The spatial assessment shows that some radiation hazard indices are higher than the global average values. The produced maps show that the observed increase in uranium and thorium concentrations could be related to the spread of phosphate-rich rock compositions.     

Analytical procedure for the determination of thorium, zinc and potassium in diet samples

Instrumental neutron activation analysis (INAA), and atomic absorption spectrometry (AAS) have been used for the determination of trace amounts of thorium, zinc, and potassium in diet samples. Interlaboratory comparison has been made. The z-scores show that INAA can be used to determine thorium and zinc whereas AAS can be employed to determine potassium in diet samples.     

Environmental assessment of heavy metal and natural radioactivity in soil around a coal-fired power plant in China

Concentrations of heavy metals and natural radionuclides in soil around a major coal-fired power plant of Xi’an, China were determined by using XRF and gamma ray spectrometry, respectively. The measured results of heavy metals show that the mean concentrations of Cu, Pb, Zn, Co and Cr in the studied soil samples are higher than their corresponding background values in Shaanxi soil, while the mean concentrations of Mn, Ni and V are close to the corresponding background values. The calculated results of pollution load index of heavy metals indicate that the studied soils presented heavy metal contamination. The concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the studied soil samples range from 27.6 to 48.8, 44.4 to 61.4 and 640.2 to 992.2 Bq kg^?1 with an average of 36.1, 51.1 and 733.9 Bq kg^?1, respectively, which are slightly higher than the average of Shaanxi soil. The air absorbed dose rate and the annual effective dose equivalent received by the local residents due to the natural radionuclides in soil are slightly higher than the mean values of Shaanxi. Coal combustion for energy production has affected the natural radioactivity level and heavy metals (Cu, Pb, Zn, Co and Cr) concentrations of soil around the coal-fired power plant.     

Preliminary studies on 226Ra, 228Ra, 228Th and 40K concentrations in foodstuffs consumed by inhabitants of Accra metropolitan area, Ghana

Knowledge of radioactivity levels in human diet is of particular concern for the estimation of possible radiological hazards to human health. However, very few surveys of radioactivity in food have been conducted in Ghana. The natural radionuclides ²²⁶Ra, ²²⁸Ra, ²²⁸Th and ⁴⁰K were measured in the foodstuffs using gamma ray spectrometry. All samples were found to contain high ⁴⁰K content in the range 87.77?C368.50?Bq?kg^?1. The maximum concentration of ²²⁸Th and ⁴⁰K were found in cassava to be 14.93?±?3.86 and 368.50?±?19.20?Bq?kg^?1, respectively. The total annual committed effective dose was estimated to be 4.64?mSv. The daily intake of radionuclides from food consumption reveals that cassava and plantain are the highest contributors, while millet is the lowest. The daily radionuclide intake from the foodstuffs consumed by the general public was 411.32?Bq and the daily internal dose resulting from ingestion of the radionuclides in the foodstuffs was 0.01?mSv. The radionuclide concentrations were comparable with those reported from other countries.