Preparation and calibration of a 231Pa reference material

A ²³¹Pa reference material has been characterized for amount of protactinium. This reference material is primarily intended for calibration of ²³³Pa tracers produced for ²³⁵U–²³¹Pa model age measurements associated with nuclear forensics and nuclear safeguards. Primary measurements for characterization were made by isotope dilution mass spectrometry of a purified ²³¹Pa solution using a ²³³Pa isotopic spike. The spike was calibrated by allowing multiple aliquots of the ²³³Pa spike solution to decay to ²³³U and then measuring the ingrown ²³³U by isotope dilution mass spectrometry using a certified uranium assay and isotopic standard as a reverse-spike. The new ²³¹Pa reference material will simplify calibration of the ²³³Pa isotope dilution spikes, provide metrological traceability, and potentially reduce the overall measurement uncertainty of model ages.

     

Uranium series disequilibrium in the coastal surface sediments and sea water of the Arabian Sea

Nearshore surface sediments from various locations of the West Coast of India were leached by saturated ammonium carbonate solution for the extraction of uranium isotopes. The reagent chosen was found to have high efficiency for leaching uranium isotopes without attacking the mineral core of the sediment particle. The activity ratios of²³⁴U/²³⁸U are in the range of 1.11 to 1.14 and the activity ratios of²³⁵U/²³⁵U are in the range of 0.045 to 0.047. The respective activity ratios in leachates, and residues after removal of surface organic matter from the sediment particles by treatment with hydrogen peroxide and 0.05M HCl, revealed disequilibrium between²³⁸U and²³⁴U only in the surface organic matter. The activity ratios of²³⁴U/²³⁸U and²³⁵U/²³⁸U have also been determined in some seawater samples from the Arabian Sea.     

Age determination for uranium standard samples by 231Pa/235U radiochronometer

Developing different model age determination methods of uranium sample could get more information on insight into source and suspected use in nuclear forensic investigation. A procedure for the determination of model age of uranium sample using ²³¹Pa/²³⁵U radiochronometer was reported. The ²³³Pa spike used in the procedure of ²³¹Pa–²³⁵U model age determination was separated from in-house ²³⁷Np stock solution by using two TRU resin columns and three silica gel columns and calibrated by CRM U100. Model ages of CRM U010 and IRMM-1000b were presented. The model age of IRMM-1000b using ²³¹Pa/²³⁵U radiochronometer were older than the literature reported results by ²³⁰Th/²³⁴U radiochronometer by amounts exceeded the expanded uncertainty.

     

Studies on the geochemical behaviour of uranium isotopes in coastal environment of the east coast of india

Samples of coastal marine sediments of the East Coast of India were leached with a saturated solution of ammonium carbonate for the extraction of uranium from the sediment particle surface without attacking the mineral core of the particles. All the sediment samples were found to exhibit a²³⁴U/²³⁸U activity ratio in the range of 1.07 to 1.14. On removal of surface organic matter, the²³⁴U/²³⁸U activity ratio is close to 1.00, indicating that the anomaly between²³⁸U and²³⁴U exists only on the labile surface layer. However, no such variations are observed in²³⁵U/²³⁸U activity ratios. These ratios are close to 0.045 which is the same as that of natural uranium.     

Measurement of the <Superscript>231</Superscript>Pa/<Superscript>235</Superscript>U ratio for the age determination of uranium materials

The paper describes the age (production date) determination of uranium reference materials using the ²³¹Pa/²³⁵U ratio. Direct addition of ²³⁷Np in secular equilibrium with its ²³³Pa daughter was chosen instead of the regular milking of ²³⁷Np to avoid possible loss of Pa. Sample preparation consists of a fast, one-step procedure. The developed method using ICP-MS for the measurement of ²³¹Pa is more precise than alpha spectrometry and is applicable for freshly produced low-enriched uranium materials. The measured ages are in good agreement with the reported production dates, thus the ²³¹Pa/²³⁵U chronometer can be applied for validation of ²³⁰Th/²³⁴U in nuclear forensics and safeguards.     

Anomalous behaviours of protactinium in the acid-leaching experiments on pitchblende

A series of leaching experiments with H₂O, HCl, HNO₂ and HF were carried out on a sample of pitchblende from Africa. Anomalously high²³¹Pa/²³⁵U ratios, which were not accompanied by similar enhancements of²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios, were observed in some uranium fractions. The observed²³¹Pa/²³⁵U ratios varied between the values of 0.035±0.005 and 2,000±300 (Ci/Ci). These results are interpreted as due, primarily, to the difference in the chemical properties of protactinium and uranium, rather than to the alpha-recoil effects.     

Variation of <Superscript>231</Superscript>Pa, <Superscript>230</Superscript>Th and <Superscript>231</Superscript>Pa<Subscript>ex</Subscript>/<Superscript>230</Superscript>Th<Subscript>ex</Subscript> 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 ²³¹Pa_ex/²³⁰Th_ex were ranged from 0.07 to 0.13 at all sampling stations. The high ²³¹Pa_ex/²³⁰Th_ex 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 ²³⁰Th_ex (90–95%) in comparison with ²³¹Pa_ex at all stations can be attributed to less efficiently scavenged of ²³⁰Th onto particles prior deposited at the marine sediment bed.     

Determination of 231Pa in Monazite and Other Streams of the Thorium Production Cycle

Monazite (chief source of thorium) which is available in plenty in the beach sands of Kerala, India, contains uranium in the range of 0.25% to 0.35%. An attempt has been made to estimate ²³¹Pa in monazite and the corresponding process stream samples of the thorium production cycle. This paper reports the ²³¹Pa activity in these samples, after coprecipitation of ²³¹Pa on MnO₂ carrier and estimation by -ray spectrometry. The estimation shows about 1000 Bq/kg of ²³¹Pa in monazite. This is the first reported estimate of ²³¹Pa in monazite.     

Simultaneous determination of trace uranium and thorium by radiochemical neutron activation analysis

A method for the simultaneous, radiochemical neutron activation analysis of uranium and thorium at trace levels in biological materials is described, based on a technique known as LICSIR, in which a double neutron irradiation is employed. In the first, long irradiation²³³Pa (27.0 d) is induced by neutron capture on²³²Th and then the sample is cooled for several weeks. A second short irradiation to induce²³⁹U (23.5 m) is followed by a rapid sequential radiochemical separation by solvent extraction of²³⁹U with TBP and²³³Pa with TOPO. Chemical yields of²³⁹U and²³³Pa were measured for each sample aliquot using added²³⁵U and²³¹Pa tracers from the -spectra of the separated fractions. The technique was validated by quality control analyses.     

Studies on the geochemical behaviour of uranium isotopes in Tuwa springs and Khari river sediments

High activities of radium were observed in the spring waters of Tuwa in Panchamahal district of Gujarat state. These determinations have led to further studies on geochemical behaviour of uranium in the surface sediments of this region. Labile uranium from the surface of the sediment particles is leached with saturated solution of ammonium carbonate. Uranium is chemically separated from the leachates by cellulose column chromatography. Unusually high activity ratios of²³⁴U/²³⁸U in the range of 2.3 to 2.77 were observed on the surface of the particles. The core of the particles exhibited a ratio of 1.00 indicating soluble²³⁴U fraction has migrated.     

Anomalous behaviour of uranium isotopes in backwater sediments of Zuari river

The surface leaching of the labile component of uranium has been carried out in estuarine sediments of Zuari river in Goa. The measurements of alpha activities of²³⁸U,²³⁵U and²³⁴U in the leachates indicated a remarkable anomaly between the activities of²³⁸U and²³⁴U. The activity ratios of²³⁴U/²³⁸U in these leachates have been found to be in the range of 1.10 to 1.14. However, the activity ratios of²³⁵U/²³⁸U have been found to be 0.045 which is close to that in natural uranium. It has also been observed that the anomaly between²³⁸U and²³⁴U exists only on the surface organic layers of the backwater sediments of the Zuari river.     

Reinvestigation of low-lying levels of231Th

Low-lying excited levels of²³¹Th fed through α-decay of²³⁵U were investigated by using α-γ and γ-γ coincidence technique. From the analyses for co-relating energy levels and transition intensities, we found that the most favorable transition from 205.3 keV ([631]7/2) level that is fed by the most dominant α transition from²³⁵U is 19.6 keV transition (205.3 keV [631]7/2⁻→185.7 keV [631]5/2⁻). We also found that the transition probability of 109.2 keV, 205.3 keV [631]7/2⁻→96.1 keV [633]9/2⁺, was corrected to be weak. These findings can explain why the 185.7 keV γ-ray is so strongly observed, 0.57 photons/ga, in the γ-spectrum associated with the α-decay of²³⁵U. The decay scheme of²³¹Th levels previously reported has been modified according to the present analysis.     

Radioactive series disequilibria in underground uranium deposits of the Singhbhum Shear Zone, Eastern India

Radionuclides of the ²³⁸U series (²²⁶Ra, ²¹⁰Pb, ²³⁴Th and ²³⁴U), ²³⁵U series (²²⁷Ac and ²³¹Pa) and ²³²Th series (²²⁸Th and ²²⁸Ra) series were measured by High Resolution Gamma Spectrometry system in twenty-five uranium ore samples from underground uranium deposits in the Singhbhum Shear Zone of Eastern India. The activity concentrations were observed to vary within a wide range in most of the deposits, as is the case in most rocks of crustal origin. The uranium ore from these deposits were not of high ore grade (U concentrations ranged from 0.015 to 0.082%). Activity ratios of key daughter–parent pairs from the decay chains, viz. ²²⁶Ra/²³⁸U, ²²⁶Ra/²¹⁰Pb, ²³¹Pa/²³⁵U, ²²⁷Ac/²³⁵U, ²³⁰Th/²³⁸U, ²³⁴U/²³⁸U, ²²⁶Ra/²³⁰Th and ²²⁸Th/²²⁸Ra indicated migration/accumulation of uranium and radium in some samples. The ²²⁶Ra/²³⁰Th ARs suggested that the deposits were not closed to groundwater movement for a maximum time period of 8ky. Thiel plot of the ²³⁴U/²³⁸U vs. ²³⁰Th/²³⁸U activity ratios indicated uranium accumulation and complex processes of uranium redistribution.     

Precision and accuracy in the determination of plutionium-239 /uranium-233, americium-241/ uranium-233 and curium-244 /uranium-233 alpha activity ratios by alpha spectrometry

Determination of²³⁹Pu/²³³U,²⁴¹Am/²³³U and²⁴⁴Cm/²³³U alpha activity ratios is required when using²³³U as a tracer for the determination of plutonium, americium and curium by alpha spectrometry. Precision and accuracy in the determination of these alpha activity ratios was evaluated by preparing synthetic mixtures from solutions of enriched isotopes of²³⁹Pu,²⁴¹Am,²⁴⁴Cm and²³³U. Separate synthetic mixtures were prepared for each of the three alpha activity ratios. The sources from the synthetic mixtures were prepared by direct evaporation method using tetra ethylene glycol /TEG/ as a spreading agent, alpha spectra were recorded by employing solid state silicon surface barrier detectors coupled to a 4 K analyzer and the alpha spectra were evaluated by a method based on the geometric progression decrease for the far tail of the spectrum. Large area detector /i.e. 450 mm²/ was observed to reduce the effect of nonhomogeneous distribution, if any, of the two elements present in the source. Precision and accuracy of about 1% is demonstrated for the determination of²³⁹Pu/²³³U,²⁴¹Am/²³³U and²⁴⁴Cm/²³³U alpha activity ratios using large area silicon surface barrier detector.     

The leachability of some natural and man-made radionuclides from soil and sediments on acid attack

A radiotracer study was made of the leachability of some natural and man-made radionuclides from soils and sediments subjected to attack by various acid mixtures. Particular attention was paid to the nuclides²³⁸U,²³²Th, Pa (as²³³Pa) and Np (as²³⁹Np), since for these neutron activation can be used to study recoveries and/or to induce in situ radionuclides in samples. Thus conventional NAA allowed determination of total²³⁸U and²³²Th instrumentally, and also enabled analysis of leachates and residues by radiochemical or instrumental NAA. Activation of these nuclides produced samples endogenously labelled with²³³Pa and²³⁹Np whose behaviour on acid dissolution/leaching could be examined. Furthermore, comparison of neutron irradiated and non-irradiated samples allowed us to investigate the possibility of increased leachability induced by nuclear recoil reactions; however, this effect was negligible. We also investigated the acid leaching of americium adsorbed on the surface of sediment. In general, unsatisfactory leaching recoveries were found for²³³Pa,²³⁹Np and²³²Th for most materials, indicating the need for total dissolution procedures.     

Natural radionuclides and 137Cs activity concentration in the bottom sediment cores from Kuwait Bay

Summary The activity concentration of natural radionuclides and ¹³⁷Cs in the bottom sediments cores from Kuwait Bay have been determined by γ-ray spectrometry. Particular attention was devoted to the exact determination of two uranium isotopes: ²³⁵U and ²³⁸U in order to find any presence of depleted uranium dispersed during the 1991 Gulf War. The calculated ²³⁸U/²³⁵U activity ratios for all the surface (15 cm) as well as the core profile (up to 70 cm in depth) samples were within the limit of one standard deviation close to the value of 21.5 for natural uranium. Simultaneous instrumental determination of the unsupported ²¹⁰Pb and ²²⁶Ra in a few sediment core profiles was used for quantification of sediment accumulation rates. The calculated sedimentation rates (for the constant atmospheric ²¹⁰Pb flux rate - CRS model) ranged from 0.2 to 0.6 cm ^. y^-1 and were close to the data calculated by the Weibull distribution of ¹³⁷Cs in undisturbed sediment cores.     

Precise measurement of the hyperfine splitting and isotope shift of8S7/2→10P9/2 transition in241Am and243Am atoms

The study of physico-chemical and biotic processes in the environment is essential to understanding the behavior of transuranic nuclides and to assess their environmental impact. Dialysis, ion exchange, and co-precipitation techniques have been used to study speciation. The dissolved fraction of^239,240Pu in coastal waters of Bombay harbor bay and in interstitial water from bottom sediments of the bay were found to be associated with organic matter. The desorption of Pu from sediments in coastal waters is influenced by salinity and carbonate. Studies indicate that, even from anoxic sediments, remobilization and the potential for migration is not significant.     

Thorium series disequilibrium and geochemical processes in estuarine sediments of Mandovi river

The measurements of natural radioactivity due to thorium isotopes have been carried out in estuarine sediments of Mandovi river (Goa). The geochemical behaviour of these sediments has been studied by leaching the samples with 5 % ethylenediaminetetraacetic acid at pH 3.0 in order to investigate the processes occurring on the surface of the sediment particles and the distribution of natural thorium in estuarine sediments. The²²⁸Th/²³²Th activity ratios have been found to be in the range of 2.00 to 2.12. This anomaly between²³²Th and²²⁸Th has been attributed to the preferential leaching of²²⁸Ra by water flowing over these sediments. The activities of²²⁸Ra on the surface labile layers of the sediments have also been determined. The²³⁰Th/²³²Th activity ratios have been found to be in the range of 0.94 to 1.04. These ratios are mainly dependent on the precipitation action of²³⁰Th on adjacent sediments.     

Determination of weight distribution ratios of Pa(V) and Np(V) with some extraction chromatography resins and the AG1-X8 resin

Literature data on distribution ratios (D_w) of Np(V) and Pa(V) for the AG1-X8 resin are scarce whereas those related on resin capacity factors (k′) values for TEVA, TRU and U/TEVA resins are absent. Therefore, batch extraction experiments for Pa(V) and Np(V) from HCl and HNO₃ media were realized, at tracer scale, with AG1-X8 and EIChroM resins (TEVA, TRU and U/TEVA). Based on the new D_w and k′ values obtained in this study, a new protocol for Pa/Np separation has been developed leading to a better separation factor of 10⁵ and a chemical yield of 97 ± 3% and 99 ± 1% for Pa and Np, respectively. A separation of ²³¹Pa from uranium matrix was successfully tested.     

The transfer of uranium from sediment to water along Jucar River, Spain

The effect of sediment size, pH, temperature and conductivity on the transfer of uranium from sediment to water has been studied. The uranium concentration and the²³⁴U/²³⁸U,²³⁵U/²³⁸U activity ratios were measured in water, sediments and suspended matter sampled from Jucar River, using low level alpha-spectrometry. Distribution factors were obtained from these measurements. A more detailed sampling was done in the neighbourhood of the Cofrentes Nuclear Plant (Valencia, Spain). Total uranium activity,²³⁴U/²³⁸U activity ratio and distribution factors for²³⁴U and²³⁸U were found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes.