The paper deals with one of the most urgent aspects of irradiation hygiene, namely assessment of risk for irradiation-induced cancers of the thyroid. A model is described to predict high mortality rates of thyroidal cancer in the population due to the catastrophe at the Chernobyl Atomic Power Station. With the model, life-time risk rates involving sex and age at the moment of irradiation, as well as an irradiation mode.
The qualitative and quantitative parameters of hemopoiesis and immunocompetent cells were studied in 365 children in the early "iodine" and long-term periods after the accident. In accordance with primary response, a group consisting of 28 subjects with so-called "radiation injury" was distinguished. The early period was marked by unusual qualitative and quantitative hematological changes which, however, did not lead to the development of the hematological syndrome characteristic of acute radiation injury. Certain deviations that corresponded to somatic pathology were detectable at the late periods after the accident.
Following the Chernobyl accident many activities were conducted in Ukraine in order to define the radiological impact. Considered here are gamma spectrometric analyses of soil-depth-profile samples taken in the years 1988-1999, gamma spectrometric measurements of radionuclide concentration in soil samples taken in 1986, and measurements of external gamma-exposure rate in air. These data are analyzed in this paper to derive a "reference" radionuclide composition and an attenuation function for the time-dependent rate of external gamma exposure that changes due to the migration of radiocesium into the soil column. An attenuation function for cesium is derived that consists of two exponential functions with half lives of 1.5 and 50 y. The dependencies of attenuation on direction and distance from the Chernobyl Nuclear Power Plant are also demonstrated. On the basis of these analyses the average individual and collective external gamma doses for the population of Ukraine are derived for 1986, 1986-2000, and 1986-2055. For the 1.4 million persons living in rural areas with 137Cs contamination of >37 kBq m(-2), the collective effective dose from external exposure is estimated to be 7,500 person-Sv by the end of 2000. A critical group of 22,500 persons who received individual doses of >20 mSv is identified for consideration of increased social and medical attention.
Overall 1580 children from the regions with unsafe radiation situation were examined comprehensively at different times after the accident. The data obtained were correlated to the results of examining 610 children of the control group. The basic group children manifested a higher incidence of diverse alterations on the part of many organs and systems, which was accompanied by an increase of free radical processes signs of destabilization of cellular membranes, activation of blood cell metabolism, suppression of the T cell component of immunity in the presence of vegetovascular dysfunction. A tendency was noted toward normalization of these alterations seen over time after the accident. No clear-cut dose-effect dependence was found.
The biological effects of cosmic rays and ionising radiations on man are described. Particular attention is paid to the consequences of the environmental pollution caused by the Chernobyl accident and the relationship between I131 radiation and thyroid tumours is analysed.