Implications of postmortem human tissue analysis on biokinetic models for actinides

Changes and refinements to original biokinetic models, based on postmortem radiochemical measurements of the concentration and distribution of actinides in tissues obtained from volunteer donors with known occupational experience with actinides, are discussed with emphasis on applications to operational health physics. Analysis of five whole body donations to the United States Transuranium Registry indicates that the²³⁹Pu model put forth in ICRP Publication 30 is generally applicable, although there is a significant fraction missing from the model that is retained in the muscle. For²⁴¹Am, the more recent model put forth in ICRP Publication 48 fits the autopsy data better than the model in Publication 30, although the observed retention half-time in the liver is on the order of two to three years rather than 20 years proposed by the model. An estimated 20% of the initial systemic deposition for²⁴¹Am goes to the muscle, where it has a residence half-time estimated at ten years. For both Pu and Am, less than 5% of the skeletal actinide in the skeleton is found in the marrow. The highest concentrations appear to be associated with the periosteum and endosteum. A significantly greater fraction of inhaled Pu and Am is retained in the lungs than is predicted by current models. Differences in the actinide distribution between lung and the associated lymph nodes are observed in smokers as compared with non-smokers.     

Radionuclide detection by ion-chromatography and on-line ICP/MS and beta detection: Fission product rare earth element measurements

Separation and analysis of²³⁵U fission produced rare earth elements (REE) is described. Rare earth elements were separated using a high presure ion chromatographic separation where by each rare earth is isolated and individually detected. Detection is performed by inductively coupled plasma mass spectrometry (ICP/MS) and solid scintillation beta counting. The resulting detection methods allow complete evaluation of all stable (non-radioactive) and many radioactive REE fission products. The two detection methods (ICP/MS and Beta) illustrate how mass selective and radiometric data can be used to provide complimentary information regarding the isotopic characterization of radioactive samples.Pacific Northwest Laboratory is operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.     

Creation of variable concentrations of defects on TiO2(110) using low-density electron beams

Low density (˜μA/cm²) 0.48 and 1.0 keV electron beams have been used to create surface defects on a TiO₂(110) surface. These electron-beam induced defects were examined primarily by X-ray photoelectron spectroscopy (XPS) with supporting ultraviolet photoemission spectroscopy (UPS). Glancing and normal emission XPS spectra of nearly defect-free surfaces revealed that Ti atoms on the surface were similar to the bulk Ti, while some surface oxygen atoms were different from the bulk oxygen. XPS of Ti 2p_3/2 was used to quantify the defect concentration and to examine the defect electronic structure. Based on our calculation of defect concentrations and the comparison of our results with results and models from the literature, we conclude that oxygen vacancies induced by electron beams in the current study are mostly from the bridging oxygen sites, in agreement with the previous work. A range of defect concentrations with similar electronic structure, mainly composed of Ti³⁺, have been induced by low-density electron beams. Beam energy and exposure were the experimental variables. The rates of defect formation at low beam exposure were beam-energy dependent, with a faster growth rate at 0.48 keV than at 1.0 keV. These defects were similar to those by thermal annealing in vacuum, but a higher concentration of defects could be obtained with longer beam exposure. However, the e-beam induced defects were different from those produced by Ar⁺ ion bombardment since both this and previous studies have found defects produced by Ar⁺ ion bombardment to be complex, with a variety of different local environments where oxygen and titanium surface atoms coexist.     

The measurement of222Rn in drinking water by low-level liquid scintillation counting

Radon-222 (Rn) has universally been found in well water. Non-stagnant ground water is collected at the well head while the well is pumping. The water is adjusted to a slow, non-aerated, steady flow through a clear tube, and a 500 ml glass bottle is filled. The sample is tightly capped after a high meniscus has developed. In the laboratory, standard 22 ml glass vials are filled with 10 ml of a toluene based mineral oil LS cocktail. Then, two 5 ml sample aliquots are pipetted into the vial. Vials are capped tightly, shaken vigorously, and placed in the liquid scintillation (LS) counter. Secular equilibrium is established in approximately 4 hours, after which samples are counted for 100 minutes each. The counting efficiency for Rn and progeny ranges between 315 to 345 percent depending on the chosen spectral window. The average background is about 6 cpm. A total of 28 wells were tested for Rn in the Carefree-Cave Creek, Arizona, USA area. The area's geometric average Rn concentration was found to be 46.5 Bq·l^–1. The associated estimated lung dose is 0.51 mSv·y^–1.Deceased 1 June 1991.     

Experimental limitations in impedance spectroscopy: Part VI. Four-point measurements of solid materials systems

Four-point impedance spectroscopy of solid materials systems is severely hampered by unavoidable voltage-divider effects associated with the reference electrodes. As demonstrated by test circuit studies and experiments with Pt/YSZ/Pt cells (with embedded silver reference electrodes), high impedance reference electrodes can produce distorted and erroneous impedance data. The relationships between these data and the sample properties (conductivity, dielectric constant) and instrument limitations (input impedance/capacitance) are derived. Successful four-point impedance measurements on conductive systems require large effective dielectric constants, which may be unattainable in bulk solids, but are often associated with internal interfaces.     

Stochastic radiative transfer in multilayer broken clouds. Part I: Markovian approach

A two-part paper describes the statistical treatment of solar radiative transfer in multilayer broken clouds. The proposed approach is a logical development of the statistical ones originally suggested for a single-layer broken clouds. This first part introduces a new statistically inhomogeneous Markovian model that allows one to properly account for different combinations of the random and maximum overlap of broken clouds at distinct vertical layers. The statistically inhomogeneous Markovian model and the stochastic radiative transfer equation have been used to derive equations for the mean radiance of solar radiation. It was demonstrated that in extreme cases the obtained equations agree with corresponding equations previously derived for (i) the statistically homogeneous broken clouds and (ii) the vertically inhomogeneous overcast clouds.     

Radiological characterization of neutron-activated metal wastes from nuclear power stations

Three different methods for determining the long-lived radionuclide contents of highly neutron activated metal wastes are being compared and assessed using samples of pressurized-water reactor (PWR) and boiling-water reactor (BWR) spent fuel disassembly hardware and control rods. These methods include: 1) empirical analyses involving sampling and laboratory measurements; 2) direct assay techniques; 3) calculation methods. These techniques are discussed and the results of the comparisons made to date are presented. The agreement between empirical versus calculational methods for the disassembly hardware was generally within 10% to 50%, and rarely exceeded a factor of 2.5, especially near the fueled region of the reactor core. However, large discrepancies between the measured versus calculated concentrations were observed for⁵⁹Ni and⁶³Ni at the end fittings of the fuel assembly hardware, where the calculations underestimated the concentrations by factors varying from about 8 to 28. The calculation errors are believed to be due to inadequate cross section data for the nickel isotopes.Pacific Northwest Laboratory is operated for the U. S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.     

Electron-stimulated desorption of D (H) from condensed D2O (H2O) films

The electron-stimulated desorption (ESD) of D⁻ and H⁻ ions from condensed D₂O and H₂O films is investigated. Three low-energy peaks are observed in the ESD anion yield, which are identified as arising from excitation of ²B₁, ²A₁ and ²B₂ dissociative electron attachment (DEA) resonances. Additional structure is observed between 18 and 32 eV, which may be due to ion pair formation or to DEA resonances involving the 2a₁ orbital. The ion yield resulting from excitation of the ²B₁ resonance increases as the film is heated. We attribute the increase in the ion yield to thermally induced hydrogen bond breaking near the surface, which enhances the lifetimes of the excited states that lead to desorption.     

Real-time airborne radiation analysis and collection (RTARAC) searching for airborne species characteristic to nuclear proliferation

An effective means of detecting airborne radioactive aerosol plumes has been developed and tested on aircraft platforms. The Real-Time Airborne Radiation Analysis and Collection (RTARAC) system was mounted in the wing pod of a Navy P-3 where it sampled 20 cubic meters of air per minute on each of eleven sequentially advanced filters. A 140% intrinsic gemanium detector counted radioactive particles collected on the 15 cm circular filters in real-time. Gamma-energy spectrum and near real-time analysis of the sample were displayed on a laptop computer.     

Barrier-free intermolecular proton transfer in the uracil-glycine complex induced by excess electron attachment

The photoelectron spectra (PES) of anions of uracil-glycine and uracil-phenylalanine complexes reveal broad features with maxima at 1.8 and 2.0 eV. The results of ab initio density functional B3LYP and second order M?ller-Plesset theory calculations indicate that the excess electron occupies a π^* orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT) from the carboxylic group of glycine to the O8 atom of uracil. As a result, the four most stable structures of the anion of uracil-glycine complex can be characterized as the neutral radical of hydrogenated uracil solvated by the anion of deprotonated glycine. The similarity between the PES spectra for the uracil complexes with glycine and phenylalanine suggests that the BFPT is also operative in the case of the latter anionic species. The BFPT to the O8 atom of uracil may be related to the damage of nucleic acid bases by low energy electrons because the O8 atom is involved in a hydrogen bond with adenine in the standard Watson-Crick pairing scheme. Received 6 April 2002 Published online 13 September 2002