M. Sankar Das

Trace element characteristics, REE patterns and partition coefficients of zircons from different geological environments—A case study on Indian zircons

Abstract Twelve zircon separates from diverse geological settings in peninsular India have been analyzed for their Zr, Hf, Sc, REE, Th and U contents employing neutron activation techniques. The whole rock samples of acid charnockite and a related rock of syenitic composition were also analyzed for these elements after separation of zircons. The study reveals that 1. a) the zircons exhibit a wide range of variation in elemental abudances and their ratios, 2. b) their chondritic normalised REE patterns exhibit negative or positive Ce and negative Eu anomalies in addition to smooth HREE enriched patterns without anomalies, and 3. c) there are significant differences in the REE partition coefficients of zircons from the charnockite and the associated syenite. The overall elemental abundances and REE patterns of the zircons could be explained in terms of crystallochemical factors, bulk compositional differences of parent melts and paragenetic histories.

Growth of hair and the trace element profile a study by sectional analysis

Correlations between the growth of hair and the trace element profile have been investigated by non-destructive neuron activation analysis through gamma-ray speetrometry using NaI(Tl) as well as Ge(Li) detectors. After preliminary investigations to establish the experimental errors, the effect of washing procedures and in-person variations, hair samples belonging to ladies with known case histories, particularly with regard to dietary habits, health and profession, were examined. Scalp-hair samplex 50–100 cm in length, representing an average time span of ∼5–10 years were collected by combing. Samples in their non-anagen phase, differentiated by their roots, were analysed in 10 cm sections. The concentrations of the following elements were determined: Na, Cl, Mn, Co, Cu, Zn, As, Se, Ag, I, Au and Hg. Absolute values for the concentrations are reported for most of the elements, while for the rest relative values for the various sections are given. The values for the different sections vary by large factors for many elements although for some elements, like Cu and Mn, the variations are not appreciable. The unusually large concentrations of elements like Se ang Hg are in broad agreement with the case histories. However, detailed examination of the results with regard to time-dependent variations seem to pose serious problems in the applications to forensic science.

On the fission track method for the determination of the uranium content of whole rock samples

Abstract The induced fission track technique in conjunction with internal standard addition has been used for the determination of uranium in geological samples. Convenient aliquots of the sample solution spiked with known amounts of uranium, deposited and dried on “Lexan”, were irradiated in CIRUS (thermal flux 2·10 12 n cm -2 sec -1 ; irradiation time 40 min). These irradiated “Lexan” pieces were etched with 25% (w/v) sodium hydroxide for 2 min at 200° to reveal the tracks. From a count of track densities in the “Lexan”, the uranium contents of the two USGS rock standards G-2 and BCR-1 were determined to be 2.01 and 1.64 p.p.m. of uranium, respectively; these results are in good agreement with the literature values.

Studies on the cation-exchange behaviour of Ammonium 12-molybdophosphate: Part I. Separation of Rubidium, Thallium and Caesium

The cation-exchange behaviour of ammonium 12-molybdophosphate (AMP) for thallium(I) is discussed. Conditions are described for the separation of rubidium, thallium and caesium from one another on a column of AMP suitably mixed with asbestos. The three elements are adsorbed from 5 M nitric acid. Rubidium is first eluted with 3 M ammonium nitrate. Thallium is separated by oxidative elution using bromide-bromine mixture. Caesium is finally removed by 12 M ammonium nitrate.

LOSS OF ELEMENTS IN THE OXYGEN FLASK DECOMPOSITION OF BIOLOGICAL MATERIALS: A STUDY BY NEUTRON ACTIVATION ANALYSIS

Partial loss of elements in the oxygen flask method for the decomposition of biological materials is described. The irradiated sample is placed in a platinum wire gauze or quartz cup and burnt in an oxygen atmosphere in the presence of carrier solutions. The results obtained by radiochemical neutron activation analysis for the elements like Mn, As, Cu, Sb and Zn in different standard reference materials are presented with a discussion of the possible causes for the lower values.

Determination of traces of rare earths in high-purity thorium dioxide by neutron activation analysis

Abstract The use of thorium dioxide as a nuclear fuel requires the determination of individual rare earth impurities at 0.08–1 mg kg−1 levels. Neutron activation is sufficiently sensitive but separation from the matrix is essential. In the proposed method, thorium dioxide (5–20 g) is dissolved in concentrated nitric acid with a little hydrofluoric acid; after evaporation, thorium is complexed with ammonium carbonate and the solution is passed through a small column of Chelex-100 resin which retains the rare earths quantitatively without retaining thorium. The rare earth elements are eluted with dilute nitric acid, concentrated, and irradiated with standards; after irradiation the rare earth are collected on a lanthanum carrier and measured by γ-ray spectrometry. The recoveries of rare earths were checked with tracers and by standard addition to thorium dioxide matrices. The reproducibility for La, Eu and Dy was satisfactory at 0.01, 0.003 and 0.002 mg kg−1, respectively; as was the reproducibility for all rare earths added to thorium dioxide (1–4 μg/5 g). Limits of detection are adequate for certification of nuclear-grade material.

Preparation of ion exchange resin based elemental standards for use in activation analysis

Various methods of preparing standards for activation analysis have been reported in the literature. This paper describes the feasibility of preparing ion exchange resin based standards containing predetermined levels of ions. Using a solution of known initial concentration of the ion, and given the value of its distribution coefficient, it is possible to predict the resin concentration that will be obtained. Resins containing ppm levels of copper and manganese have been prepared and their stabilities evaluated over a period of time. The feasibility of preparing a multielement standard has been studied with five rare earth elements (La, Ce, Sm, Eu and Dy).

Voltammetric determination of molybdenum in brines

SummaryThe presence of molybdenum in natural water, at the ng/ml level, is essential for the growth of phytoplankton and other organisms, but its presence in brines is reported to affect the current efficiency in electrochemical chlor-alkali production. A voltammetric method, incorporating a preconcentration step, has been developed for the determination of molybdenum at this level in brine and sea-water. Molybdenum is co-precipitated with cadmium sulphide at a pH of about 2. The precipitate is dissolved in aqua regia and fumed with perchloric acid. The residue is dissolved in a supporting electrolyte comprising 1M sodium perchlorate, 0.1M sodium acetate and 0.01M EDTA (pH 6.0±0.2). At this pH, a well-defined wave for the reduction of molybdenum(VI) is obtained at −0.88 Vvs. SCE. None of the common ions interferes. Preconcentration of the molybdenum from 1 litre of brine facilitates its determination down to 1 ng/ml. The estimated precision at the 5 ng/ml level is 13%.ZusammenfassungDie Anwesenheit von Molybdän in natürlichem Wasser in der Größenordnung von ng/ml ist für das Wachstum von Phytoplankton und anderen Organismen wesentlich, aber, wie berichtet wird, stört seine Anwesenheit in Salzwässern die elektrochemische Produktion von Chlor bzw. Alkali. Eine voltammetrische Methode mit vorangehender Anreicherung wurde für die Molybdänbestimmung in dieser Größenordnung in Salz- und Meerwasser ausgearbeitet. Molybdän wird bei pH etwa 2 mit Cadmiumsulfid mitgefällt. Dieser Niederschlag wird in Königswasser gelöst und mit Perchlorsäure abgeraucht. Der Rückstand wird in einem Trägerelektrolyt mit 1M Natriumperchlorat, 0,1M Natriumacetat und 0,01M ÄDTA (pH 6,0±0,2) gelöst. Bei diesem pH erhält man bei −0,88 V gegen eine ges. Kalomelelektrode für die Reduktion von Mo(VI) eine wohldefinierte Welle. Keines der üblichen Ionen stört. Die Anreicherung des Molybdäns aus 1 Liter Salzwasser erleichtert seine Bestimmung bis zu 1 ng/ml. Die geschätzte Genauigkeit für die Größenordnung 5 ng/ml beträgt 13%.

Studies on the234U and238U ratio in natural materials

Abstract234U to235U activity ratios were determined in some of the primary and secondary uranium minerals. The conditions for the accurate measurement of this ratio by α-spectrometry were optimized. The activity ratios of234U to238U in U4+ and U6+ fractions were determined. This ratio was found to be more than the equilibrium value in one leaching experiment and is explained as due to the oxidation and selective removal of the234U, relocated by α-recoil. Age values of some of the minerals, which had earlier been dated assuming this ratio to be one, were rectified when necessary.

A modified method for the determination of lead in zircons by differential-pulse anodic stripping voltammetry

Abstract Zircons (20–100 mg) are decomposed within 1 h by fusion with potassium hydrogenfluoride followed by fuming with sulphuric acid. With differential-pulse anodic stripping voltammetry, after deposition for 1 min, the limit of detection for lead is 2 ng ml −1 and the limit of quantitation is 6.6 ng ml −1 . Results (7–247 mg kg −1 lead) are reported for nine zircons.