Search Results

You are looking at 1 - 10 of 19 items for

  • Author or Editor: S. Clark x
  • All content x
Clear All Modify Search

Abstract  

Radiostrontium is concentrated in the shells of mollusks and other animals due to the isomorphic substitution of strontium for calcium in the calcium carbonate shell matrix. Radiochemical separation of strontium from such matrices is difficult because of the chemical similarity between strontium and calcium. This paper describes a technique using a commerically-available, solid-phase extractant to separate Sr-89 and Sr-90 from high concentrations of Ca2+. The extractant removes Sr(NO3)2 from acidic nitrate media, and strontium activities are determined via conventional -counting techniques. This method has been used to process mollusk shells collected from contaminated reactor cooling ponds at the Savannah River Site and Chernobyl Nuclear Power Plant.

Restricted access

Summary  

Uses of radioisotopes and radiation in medicine, industry, agriculture are amongst the most beneficial applications of atomic energy for peaceful purposes. The International Atomic Energy Agency aims - in accordance with its statute - to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world. The various Technical Divisions of the Agency carry out this mandate and enhance, particularly through 'manpower development activities' the nuclear applications of radiation and isotopes. Staff members of the 'Industrial Applications and Chemistry Section' in the Department of Nuclear Sciences and Applications of the IAEA have supported more than 600 trainees per year for education in nuclear and radiochemistry through fellowships, training courses and workshops. Provision of printed material in various disciplines is supporting our educational efforts.

Restricted access

Abstract  

Capillary electrophoresis (CE) is a useful method for rapid separations of metal cations. Under ideal conditions, CE can provide complete separation of the trivalent lanthanides in less than 10 min. Simple organic ligands must be included in the electrolyte matrix to achieve good resolution between the cations. In this paper, we demonstrate how to use complexation constants from the literature to design separation protocols for the trivalent f-elements.

Restricted access

Abstract  

The determination of isotopic thorium by alpha-spectrometric methods is a routine practice for bioassay and environmental measurement programs. Alpha-spectrometry has excellent detection limits (by mass) for all isotopes of thorium except232Th due to its extremely long half-life. This paper reports a pre-concentration neutron activation analysis (PCNAA) method for232Th that may be performed following alpha-spectrometry if a suitable source preparation material is utilized. Human tissues and other samples were spiked with229Th and the thorium was isolated from the sample using ion exchange chromatography. The thorium was then electrodeposited from a sulfate-based medium onto a vanadium planchet, counted by alpha-spectrometry, and then analyzed for232Th by neutron activation analysis. The radiochemical yield was determined from the alpha-spectrometric method. Detection limits for232Th by this PCNAA method are approximately 50 times lower than achieved by alphaspectrometry.

Restricted access

Abstract  

The accurate and precise determination of232Th in biological samples is very important for the development of biokinetic models for thorium and for improving our knowledge on its distribution in human tissues. Radiochemical neutron activation analysis has long been one of the most sensitive methods for the determination of232Th. However, these determinations suffer in reliability because recovery information following the separation is not typically available. This information is particularly important for difficult matrices such as human bone where recoveries may be significantly less than unity. Also, the separation of difficult matrices following neutron activation may involve relatively high personal dose from the co-activated matrix. A novel approach for the determination of radiochemical yield has been developed which employs the use of a readily available, gamma-emitting isotope of thorium,227Th.227Th, obtained by radiochemical separation from227Ac, is added to each, dissolved sample prior to separation and the chemical yield determined by gamma-ray spectrometry following the separation. This pre-concentration step is then followed by neutron activation and the232Th determined via233Pa using gamma-ray spectrometry. Detection limits were approximately an order of magnitude lower than obtained by alpha-spectrometry.

Restricted access

Abstract  

Laser-induced kinetic phosphorimetry is an accurate, sensitive and rapid alternative to radiometric determination of natural and depleted uranium in aqueous solutions. This method offers detection limits below 10 ng/l U (2.5·10−4 Bq/l natural U) and a broad analytical range to 5 mg/l U (130 Bq/l natural U). For many samples, dilution is the only sample preparation required. However, because this technique infers uranyl concentrations from time-resolved phosphorescence intensities, results are dependent upon sample matrix constituents that affect the phosphorescence of the uranyl cation. This study examines the influence of cations, anions and ligands common to natural water, process and bioassay samples on the quenching of uranyl phosphorescence and the consequences for lower limits of detection and accuracy of measurements.

Restricted access

Abstract  

A 30 Hz YAG laser pumped, narrow-line, optical parametric oscillator (OPO) has been used to investigate the chemical states of selected compounds in aqueous solution. The OPO system has the advantage that it can scan wavelengths over large ranges without significant loss of output power. The visible spectra of rare earth complexes in dilute aqueous solutions (as chemical analogs for the actinides) have been studied and preliminary qualitative results for erbium acetate complexes at the 100 micromolar level are in good agreement with literature data. Quantitative measurements of the protonation constant for phenol red at the 100 nanomolar level were measured. The particular implementation of the OPO system used in this work introduced a number of spectral artifacts due to optical signal overlap with near-infrared water absorption bands. In addition, it was demonstrated that the concentration limiting factor for photoacoustic spectroscopy is the intrisic absorption of water in the visible region of the spectrum.

Restricted access

Abstract  

The influence of elevated temperatures on the formation of 1:1 chloro complexes for Eu3+ and Am3+ are reported. Using a solvent extraction technique, stability constants for the equilibrium M(aq) 3++Cl(aq) MCl(aq) 2+ have been measured in the temperature range of 25–75 °C. Modest increases in 1 are observed, and small positive enthalpies for these reactions are reported. These data are discussed in the context of previous reports for the trivalent lanthanide and actinide chloro systems.

Restricted access

Abstract  

The simultaneous determination of multiple actinide isotopes in samples where total quantity is limited can sometimes present a unique challenge for radioanalytical chemists. In this study, re-determination of 238Pu, 239+240Pu, and 241Am for soils collected and analyzed approximately three decades ago was the goal, along with direct determination of 241Pu. The soils had been collected in the early 1970’s from a shallow land burial site for radioactive wastes called the Subsurface Disposal Area (SDA) at the Idaho National Lab (INL), analyzed for 238Pu, 239+240Pu, and 241Am, and any remaining soils after analysis had been archived and stored. We designed an approach to reanalyze the 238Pu, 239+240Pu, and 241Am and determine for the first time 241Pu using a combination of traditional and new radioanalytical methodologies. The methods used are described, along with estimates of the limits of detection for gamma-and alpha-spectrometry, and liquid scintillation counting. Comparison of our results to the earlier work documents the ingrowth of 241Am from 241Pu, and demonstrates that the total amount of 241Am activity in these soil samples is greater than would be expected due to ingrowth from 241Pu decay.

Restricted access

Abstract  

Kinetic dissolution studies were conducted on four prominent U-Ca-PO4 minerals (metaschoepite, becquerelite, chernikovite and metaautunite). Synthetic samples were contacted with four extractants (acetic acid, deionized water, EDTA and sodium bicarbonate) at room temperature at two concentrations, 100 mM and 1 mM. Dissolution progress was monitored by periodic sampling for dissolved U, and dissolution rates were obtained from fits to a three term exponential model. Significant variations were observed in the rate and extent of dissolution among the mineralsexamined. The uranyl phosphates chernikovite and metaautunite proved resistant to dissolution in non-carbonate systems, with dissolution half-times of days to weeks in 100 mM systems and weeks to years in 1 mM systems. In contrast, the uranyl oxide hydrates schoepite and becquerelite were solubilized over much shorter time scales. While 100 mM bicarbonate was successful in dissolving U in all forms, dissolution rates varied among the four minerals. Overall, EDTA was the least sensitive to a 100 to 1 mM drop in its concentration in its solubilization of all four mineral phases, underscoring the importance of organic complexation for the environmental mobility of uranium.

Restricted access