The induction of HPRT-mutations and the survival of Chinese hamster cells were studied after exposure to accelerated ⁴He and ¹²C ions with various LET (20-360 keV/mm) and to g rays. The linear-quadratic dose-effect curves were observed after exposure to radiation with LET up to ~ 50 keV/mm. They were modified to linear relationship with growing of LET. The RBE (LET) dependences have a local maximum at 80-100 keV/mm. The RBE values for the induction of mutations and chromosome aberrations were 4.8-5.0. These values are ~ 2 times larger than for the cell survival (2.3-2.9). The high heterogeneity and the chromosome instability in aneuploidy and chromosome aberration levels were observed in both spontaneous HPRT-mutants and induced ones by protons (LET ~ 0.218 keV/mm),¹⁴N ions (LET ~ 77 keV/mm) and g rays. The chromosomal instability was highest among spontaneous mutants and decreased with increasing of LET. The "metabolic hypothesis" for chromosome instability is discussed. The regularities of unstable chromosome aberration formation in human lymphocytes were studied after exposure to g rays, protons and ¹²C, ²⁴Mg, and ¹⁴N ions (LET ~ 0.218; ~ 12; 42.7 and ~ 77 keV/mm, respectively). The frequency of chromosome aberrations increases with growing of the doses and radiation LET. The RBE values were 1.0 for protons; 1.2-1.3 for ¹²C; 1.4-1.7 for ²⁴Mg, and 2.0-2.2 for ¹⁴N ions. The dose-effect dependences for chromosome aberrations and adaptive response have been investigated in human lymphocytes, Chinese hamster cells and human melanome cells after g irradiation at the doses of 0.01-1 Gy. Nonlinear dose-effect dependence for cells with aberrations was revealed for all types of cells. The hypersensitivity at the doses of 0.01-0.2 Gy and inducible radioresistance at the doses above 0.5 Gy were observed. The possible mechanisms that were involved in this phenomenon are discussed.

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