M.A. Klimovich, K.F. Sergeichev, D.M. Karfidov, N.A. Lukina, L.N. Shishkina

Nuclear power plants and radiochemical factories accidents, as well as the development of natural resources in biogeocenoses with increased radiation background cause a necessity of the equip-ment creation capable simulating the natural decay of radionuclides for studying the development of the biological consequences of chronic ionizing radiation at low doses. On basis of analysis of the lipid peroxidation regulation system (LPO) parameters a high biological effectiveness of X-ray radiation during a single irradiation of mice at doses of less than 1.5 mGy under a changing dose rate was revealed The aim of this work is the development of the equipment which generate of X-rays at low doses under decreasing dose rate during radiation and the estimation of biological effectiveness of such exposure. The X-ray source of a new type was created on the ground of the super high frequency elec-tronic cyclotron resonance electron accelerator by a microwave field in a mirror trap. The hard X-rays is generated by the interaction of plasma with the walls of the vacuum camera, and the in-tensity and energy of radiation decrease with increasing pressure in the camera. The experiments were performed on adult outbreed mice (females), 12 - 13 weeks ago. Expe-riments were repeated three times, the antioxidant status of the murine tissues is modified by carrying out of experiments at different seasons: November - December (experience № 1), Sep-tember - October (experience № 2) and May - June (experience № 3). The animals were exposed once during 17-18 minutes for the first half of the day. The dose range is within from 0.24 mGy to 1.43 mGy. The decapitation of mice are performed in the experiment № 1 within 7 and 30 days, № 2 and № 3 within 30 and 37, 31 and 38 days respectively after irradiation. All parameters in organs were measured for each animal, blood plasma were combined from 2 - 3 species. Since the LPO regulation system plays an important role both for the regulation of cellular metabolism in tissues of intact animals and the development of the biological consequences of io-nizing radiation at a wide range of doses, the biological effectiveness of X-rays at low doses under changing dose rate was estimated by its influence on the content of products, reacting with 2-thiobarbituric acid in the liver and brain homogenates and the blood plasma, as well as the amount of diene conjugates (DC) and ketodienes (KD) in the lipid organs, the oxidation degree of lipid or their ability to decompose peroxides, that is the antiperoxide activitiy (APA). Significant seasonal differences in the intensity of LPO and physical-chemical characteristics of the mice lipid tissues were revealed. It is shown that the biological effect of X-rays at low doses under changing dose rate are complex, nonlinear, depending on the initial values of the LPO pa-rameters. The content of TBA - reactive substances in the blood plasma is the most sensitive pa-rameter to the action of X-ray at low doses. Under X-ray action at low-doses, the significant changes of the TBA - reactive substances content are revealed in the brain homogenates in the experiments № 2 and № 3 within 30 and 31 days respectively, in the liver homogenates in the ex-periment № 2 within 31 days; in the blood plasma in all experiments within a month after radia-tion. APA has high variability in the liver and brain lipids for the groups of control animals, how-ever the heterogeneity of the lipid characteristics increases after X-ray exposure. So, peroxides in the lipid organs from individual animals were found in the experience № 2. The absences of a direct correlation of the dependence on the total dose were revealed all studied parameters in liver, brain and blood plasma. The dose rate of the low intensity X-ray primary influence on the formation of biological consequences in the blood plasma, especially at doses less than 0.5 mGy, influence of the X-ray dose rate is revealed by doses more than 0.5 mGy in the brain. The complex of the obtained results evidences both the biological effectiveness of radiation at the doses less than 1.5 mGy under changing dose rate and the significant contribution of the lipid characteristics for the formation of biological consequences of radiation.