Radionuclide biokinetics database (RBDATA-EULEP): an update

The main activity of the RBDATA-EULEP project is the development of an electronic database of information on the biokinetics of radionuclides after intake by inhalation, ingestion or injection. It consists of linked tables of publications and experiments, with details and comments on the materials, procedures and results. By March 2004 it contained information on more than 1600 experiments from 600 publications. It will be extended and Internet access will also be provided.     

Biokinetics of radionuclides and treatment of accidental intakes

This paper describes the objectives and reviews the progress of EULEP Working Party 5, convened under the auspices of the European Union's Fifth Framework Programme, to 'cluster' two EU-supported contracts, Biokinetics and Dosimetry of Internal Contamination (BIODOS (EU Contract FIS5-1999-00214)) and Radionuclide Biokinetics Database (EULEP) (RBDATA-EULEP (Concerted Action Contract FIS5-1999-00218), and two non-EU funded projects, Biokinetics of Radionuclides in Human Volunteers (RNHV (non-EU funded project)) and Treatment of Accidental Intakes of Radionuclides (TAIR (part funded by EULEP)).     

Dosimetric models for thorium and practical problems in assessing intakes

An overview is given of the models recommended by the International Commission on Radiological Protection (ICRP) for assessing intakes and doses, and summarises biokinetic data obtained after the deposition of different chemical compounds of thorium in the rat lung. The results emphasise the importance of using material-specific data rather than default reference values for absorption into blood. The limitations of external monitoring of the chest or urine analysis are discussed, and comments made on alternative strategies for radiological protection of the worker.     

Searching for momentum enhancement in hypervelocity impacts

In conjunction with the Los Alamos National Laboratory hypervelocity microparticle impact (HMI) team effort to produce higher impact velocities and to understand the physics of crater formation and momentum transfer, we have implemented a low noise microphone as a momentum detector on both the 6 MV Van de Graaff and 85 KV “test stand” particle accelerators. Calculations are presented showing that the impulse response of a circular membrane. When used as a momentum impulse detector, the microphone theoretically may detect impulses as small as 8.8 × 10⁻¹⁵ N s. Sensitivity of the microphone in this application is limited by the noise threshold of the electronic amplifiers and the ambient microphonic vibration of the system. Calculations lead us to anticipate detection of particles over the full range of the Van de Graaff acceleration capability and up to 7 km/s on the test stand. We present momentum enhancement data in the velocity range between 10 km/s and 20 km/s. Preliminary work is presented on momentum impulse calibration of the microphone using laser-pulse photon momentum as an impulse source.     

Microparticle impacts at ultra-high velocities: Their relation to macroparticle impacts

In recent years the Hypervelocity Microparticle Impact (HMI) project at Los Alamos has utilized electrostatically accelerated iron spheres of microscopic dimensions to generate ultra-high velocity impact experiments to about 100 km/sec, about an order of magnitude beyond the data range for precisely controlled impact tests with ordinary macroscopic projectiles. But the extreme smallness of the micro impact events brings into question whether the usual shock-hydrodynamic size scaling can be assumed. It is to this question of the validity of size scaling (and its refinement) that the present study is directed.

Impact experiments are compared in which two comparable impact events at a given velocity, a microscopic impact and a macroscopic impact, are essentially identical except that the projectile masses and crater volumes differ by nearly 12 orders of magnitude—linear dimensions and times differing by 4 orders of magnitude. Strain rates at corresponding points in the deforming crater increase 4 orders of magnitude with the size reduction. Departures from exact scaling, by a factor of 3.7 in crater volume, are observed for cooper targets—with the micro craters being smaller than scaling would predict. This is attributed to a factor 4.7 higher effective yield stress occurring in the micro cratering flow. This, in turn, is because the strain rate there is about 10⁸/sec as compared to a strain rate of only 10⁴/sec in the macro impact.

The measurement of impact craters for very small impact events leads to the determination of metal yield stresses at strain rates an order of magnitude greater than have been obtained by other methods. The determination of material strengths at these exceedingly high strain rates is of obvious fundamental importance. Results are compared to recent theoretical models by Follansbee, Kochs and Rollett.

Finally, the problem is addressed of predicting crater sizes in a target material with strain rate effects. First some basic results are recalled pertaining to the late stage equivalence of hypervelocity impacts. It is then seen, for a strain rate dependent material, that the curve of dimensionless crater volume versus impact velocity is replaced by a family of curves, each member of which is for one final crater size. The spacing of the curves is determined by the stress versus strain properties of the material.     

Dynamic microbial populations in heap leaching of zinc sulphide ore

Polymerase chain reaction (PCR) technology was used to monitor the microbial population within two 6-m-high sulphide ore heaps where zinc was bioleached. Genomic DNA was isolated from microorganisms attached to the ore particles. The microbial population varied in diversity at different heap heights and at different stages of the leaching cycle. Nine bioleaching microorganisms were identified, including iron oxidizers, sulphur oxidizers, whether mesophiles, or moderate thermophiles. No bioleaching extreme thermophiles were detected. Moderate thermophiles were present at average heap temperatures of 40 °C or higher. No moderate thermophiles were present in the top 2 m of the heaps. Mesophiles were present throughout the lifetime of the heaps and at all heap depths. Cultures of Acidithiobacilluscaldus and Sulfobacillusthermosulfidooxidans originally introduced to inoculate the heaps did not proliferate but were instead displaced by other species; no benefits were obtained from heap inoculation. The most predominant species were Acidithiobacillus thiooxidans and Acidithiobacillus albertensis. Leptospirillum sp. was not predominant in the heaps, in contrast to the dominant role this organism plays in tank bioleaching operations.     

Comparison of predicted with observed biokinetics of inhaled plutonium nitrate and gadolinium oxide in humans

The absorption kinetics to blood of plutonium and gadolinium after inhalation as nitrate and oxide in humans and animals has been studied. For each material, values describing the time dependence of absorption were derived from the studies in animals and used with the ICRP human respiratory tract model to predict lung retention and cumulative amounts to blood for the volunteers inhaling the same materials. Comparison with the observed behaviour in the volunteers suggests that absorption of plutonium and gadolinium is reasonably species independent, and that data obtained from animal studies can be used to assess their biokinetic behaviour in humans.