[en] This report contains a description of the thoron-in-breath monitor (TIBM) developed at CRNL. This monitor can be used to estimate the amount of thorium (Th-232 and/or Th-228) in humans. Thoron-in-breath monitoring is based on the fact that thoron (Rn-220) is a decay product of thorium, and hence deposited thorium produces thoron in vivo, a fraction of which will be exhaled. Experiences with the TIBM indicate that the monitoring is easy to perform and the results in terms of contaminated vs uncontaminated subjects can be easily interpreted. Work on relationships between thoron exhaled and deposited thorium and hence between thoron exhaled and dose, is continuing

[en] A mathematical model was developed to simulate the function of the lungs. The lungs are represented by 24 compartments each corresponding to a generation of the Weibel model A. In the model it is assumed that gases are transported in the lungs by convection and diffusion from one compartment to the other. Furthermore, the clearance of gases from the lungs by the blood perfusion is taken into account. The driving force of the inhalation and exhalation processes is the filling and emptying of the alveolar volume which follows a sinusoidal pattern. Mathematically the model is represented by two sets (one for inhalation, the other for exhalation) of 24 first-order coupled ordinary differential equations which were numerically integrated by means of a computer. The model predicts quite well the buildup of gases in the lungs and the washout of gases from the lungs

[en] A mathematical model was developed to simulate the metabolism of HT gas in humans. The rate constants of the model were estimated by fitting the calculated curves to the experimental data by Pinson and Langham in 1957. The calculations suggest that the oxidation of HT gas (which probably occurs as a result of the enzymatic action of hydrogenase present in bacteria of human gut) occurs at a relatively low rate with a half-time of 10-12 hours. The inclusion of the dose due to the production of the HT oxidation product (HTO) in the soft tissues lowers the value of derived air concentration by about 50%. Furthermore the relationship between the concentration of HTO in urine and the dose to the lung from HT in the air in lungs is linear after short HT exposures, and hence HTO concentrations in urine can be used to estimate the upper limits on the lung dose from HT exposures. (author)

[en] A multicompartmental model to simulate the dynamics of inert radioactive gases in the human body has been developed. In the model it is assumed that inert gas is transported through the body to various organs via the blood stream. The model can be used to study the dynamics of any inert gas whose partition coefficients are known, and is especially useful when the half-life of the radioactive inert gas is short compared with the biological transport processes. The model predicts quite well the observed wash-out of ¹³³Xe. Using this model the effective dose equivalents resulting from inhalation of radon and thoron were estimated. While the calculated value for radon agrees with the previously reported value, the value calculated for thoron was found to be about 55% lower. (author)

No abstract available

[en] Hairless rats were exposed to tritium by rubbing HT contaminated stainless steel planchets on them. The pattern of tritium excretion in the urine (n=4), shows the OBT (organically bound tritium) retention curve to be approximated by the sum of 2 exponential curves, one with a half-life of 0.4 days and another with a half-life of 1.4 days. The retention of HTO fit a single exponential curve with a half-life of 3.1 days. Exposed skin, unexposed skin, liver, muscle and blood (n=6) were assayed for HBO, and free HTO. Highest activity was found in the exposed skin, other organs with high activity are the unexposed skin and liver. Examination of the exposed skin showed HTO to be concentrated in the uppermost layers. The distribution of OBT was similar but was incorporated at a faster rate. The basal layer is exposed to a tritium concentration between 70-90% of that of the surface. The two macromolecule fractions with the highest amount of radioactivity were lipid and insoluble protein (mainly collagen)

[en] This paper describes a study on metabolism of inhaled tritiated hydrogen gas (HT) in mammals. Rats and human volunteers were exposed to HT gas for periods from one minute to ten minutes. The amount of HT that was oxidized in vivo was estimated by measuring the concentration of HTO in urine. No significant quantities of tritiated organic compounds resulting from HT gas inhalation were observed in tissues of rats and it is assumed that this holds true for humans also. The fraction of inhaled HT converted to HTO in human volunteers was found to be about 1 x 10^-4 indicating that the dose from the HTO that resulted from HT oxidiation is a significant component of the effective dose equivalent

[en] This document is a report on experiments to quantify the doses that may occur from the tritium gas that is converted 'in vivo' to tritiated water following the exposure to tritiated hydrogen gas contaminated air. This report also includes theoretical evaluation of the radiological hazards from the uptake through skin of tritium from tritiated hydrogen adsorbed on surfaces