RADIOBIOLOGICAL EFFECTS OF SECONDARY RADIATION OF THE PHASOTRON AT THE JOINT INSTITUTE OF NUCLEAR RESEARCH
On the phasotron at the Joint Institute of Nuclear Research in Dubna outbred female mice ICR(CD-1) with body mass 26-34 g were irradiated 20, 40 and 60 minutes in the field of secondary neutron radiation by 10 to 30 fractions with mean duration of about 2 min each. Mice were exposed once to 0.5 Gy of γ-quanta <sup>60</sup>Со and fractionally to 1.0 (0.5 + 0.5) and 2.0 (0.5 + 0.5 + 1.0) Gy with 5-min intervals with the dose rate of 12.46 cGy/min. Thymus and spleen mass values, number of bone marrow cells, peripheral leukocytes count and chromosomal aberrations in marrow cells and their mitotic activity in 24 hours after irradiation were indicative of a much stronger bio-effect from exposure in the neutron field as compared to standard γ-radiation. Relative bio-effectiveness estimated from the number of bone marrow cells and their mitotic activity lies in the range from 1.89 to 7.7. The unambiguous consequence for the central nervous system was neurotic conditions of animals after 22 hours since irradiaiton, and distortion of the excitation/inhibition ratio. It was shown that a mixed neutron, proton and photon field approximating the field of the secondary neutron component inside spacecraft during solar proton events possesses a high radiobiological effect. This finding will allow a more adequate evaluation of radiation risks in space missions.