Biodistribution, retention and elimination of fissionable elements in the internal contamination

For different internal contaminations obtained by ingestion, inhalation, absorption by skin and through wounds, using very high sensitive analysis methods such as the fission/alpha track methods, the biodistribution of the fissionable elements (U and/or Th) and the contents of these elements retained in each vital organ of the laboratory animals have been studied. In all studied cases, the rats of Wistar-London breed were used as laboratory animals. Their internal contaminations were performed in the Nuclear Medicine Laboratory in the Institute of Physics and Nuclear Engineering, Bucharest using adequate methodologies. For the internal contamination of animals, chemical compounds p.a. of the contaminant elements were used either in solutions calibrated in the fissionable element of interest or in fine powder states for the internal contamination by inhalation. The animals received established fissionable element doses which were administrated at certain time intervals. After contamination, the animals were kept in normal life conditions and under the permanent surveillance of their medical state, up to they were sacrificed. Their eliminations, urine on the filter paper and all excrement balls, were sampled every 24 hours. The vital organ samples were liver, kidney, lung, brain, heart, spleen, stomach, muscle, small intestine, large intestine and blood. These samples were weighed, calcined, re-weighed and then analyzed by one of the track detection analysis methods using the fission/alpha track micromapping technique. The utilized track detectors were the CR-39 detector, Page, England for the alpha track method and the mica-muscovite track detector for the fission track method. The used reference materials were prepared by a procedure developed by authors. The track detectors were placed adjacent to the samples (sandwich) during neutron irradiations and alpha exposures. After registration of the implied heavy charged particles, the detectors were etched in order to visualize the path of particles, which became the tracks visible by optical microscopy. Thus, in the etched track detectors, the track micromappings were obtained. These track micromappings represent the replica of the implied element atom distributions in the analyzed samples. The track densities in track detectors are proportional with the implied fissionable element concentrations of the analyzed samples and using reference materials calibrated in the element, it is possible to determine the element concentration in the unknown analyzed samples. The results obtained for the biodistribution, retention and elimination of U fissionable element in the internal contamination of experiment animals, are described in previous papers and some preliminary results for the Th internal contamination, in Radiat. Meas. in 2001. Since 2001, by the CERES Research Contract No.71/15.10.2001, the internal contamination study with Th has been continued in 2001, the biodistribution, retention and elimination of Th in the internal contamination by ingestion was studied and the results were published in the paper mentioned above. At this stage, the internal contamination by Th inhalation and the internal contamination through wounds were performed and the alpha track micromappings in CR-39 detectors were obtained. These micromappings will be studied next year, by optical microscopy. (authors)