Lifetime cancer risk estimates depend on risk projection models. While the increasing lengths of follow-up observation periods of atomic bomb survivors in Hiroshima and Nagasaki bring about changes in cancer risk estimates, the validity of the two risk projection models, the additive risk projection model (AR) and multiplicative risk projection model (MR), comes into question. This paper compares the lifetime risk or loss of life-expectancy between the two projection models on the basis of BEIR-III report or recently published RERF report. With Japanese cancer statistics the estimates of MR were greater than those of AR, but a reversal of these results was seen when the cancer hazard function for India was used. When we investigated the validity of the two projection models using epidemiological human data and animal data, the results suggested that MR was superior to AR with respect to temporal change, but there was little evidence to support its validity.
Recently artificial intelligence (AI) which has functions of our interpretations and judgments has been applied to various fields of science. In the first application of AI to the transport procedure of the radioactive material, a prototype of expert system was developed with UTI-LISP programming language to appropriately classify mainly the packages and packagings according to regulations for the safe transport of radioactive material. Classification of the packages and packagings for the consignment is mainly determined from input informations such as radionuclides, its activities, states and conveyances through a forward reasoning method of the expert system. The rationalization of practice on our interpretations and judgments for transport of radioactive material including uniformity and reliability of our decision were confirmed as the result of an application to radiation control.
Volatility of radioruthenium at room temperatures was preliminarily studied. Sulphuric acid solution containing ruthenium is placed in a glass tube with KIO4 as an oxidizing agent and tube is stirred slowly. Ruthenium is gradually oxidized and significant quantities is volatilized as the gaseous tetroxide. The influence of agitation time and concentration of stable ruthenium, sulphuric acid and oxidizing agent on volatilization were studied.
To evaluate precisely the human lung dose, it is important to know the amount of unattached atoms of radon daughter products that deposited to trachea and bronchial. The authors made a tracheobronchial tree model taking account of WEIBEL's lung model, and carried out deposition experiment of unattached atoms of radon daughter products to tracheobronchial with a flow rate of 15l/min. After sample air passed through the model, it was taken off from apparatus, and activity of particle deposited to inner wall of model was counted with a position-counter. The experiment showed that deposition fraction at generation 0 was 2.2-2.7 times value calculated from the GORMLEY and KENNEDY formula whereas values at other generations agreed with calculated ones.
Experiments were performed on the removal of radionuclides from radioactive liquid waste by reverse osmosis using asymmetric cellulose acetate membranes. In previous papers, we reported such removal properties as the dependence on solute concentration and the influence of co-existing material. In this paper we performed experiments on some separation properties, especially on the formation and the disappearance of concentration polarization layer of membrane surface. These experiments are necessary for the theoretical explanation of findings shown in previous papers. Concentration polarization layer is formed on the surface of the membrane, when pressurized feed solution is not stirred during reverse osmosis operation. This layer grows with elapsed time and reaches the equilibrium. The thickness of this concentration polarization layer and solute concentrations in this layer are calculated by a simple model. The formation and disappearance of this layer are experimented with intermittent stirring. The influence of intensity of stirring on the formation of concentration polarization layer is observed. These are important information on property of membrane for removing solute by reverse osmosis.
The direct lung monitoring and bioassay of faeces and urine are used to estimate internal exposures of alpha emitting radionuclides. The accuracy of the estimation depends on the retention and clearance model using for calculation of the biological kinetics of nuclides uptaken. The respiratory tract model described in ICRP Publication 30 is the most familiar one using for inhalation intake. The ICRP task group has proposed a new respiratory tract model to be replaced with the current ICRP Publication 30 model. In this article, a comparison of results of retention in the respiratory tract and faecal excretion calculated by the current and new models are described. The retention in the respiratory tract is calculated for 1, 000 days after acute inhalation of 1 Bq of plutonium di-oxide particles. And, the cumulative and daily excretions are calculated for 10 days after inhalation. The retention in parenchyma calculated by the new model is about a half of the current ICRP Publication 30 model. The cumulative faecal excretion in 10 days calculated by the new model is about one-third of the current model.