The aim of the experiment was to obtain new knowledge on the biological effectiveness of high-energy (300 MeV/nucleon) helium ions, which represent a part of the spectrum of cosmic rays. Male (CBA x C57BL)F1 mice, 4 months old, were exposed to a dose of 4 Gy helium ions (exposure rate 0.05 Gy/min). As a comparative standard irradiation the same dose of 4 Gy of 137Cs gamma-rays (exposure rate 0.07 Gy/min) was used. Material sampling was performed 6-8 h, 4 days and 9 days after irradiation for both experimental groups mentioned above. There were 7 animals in each group including the control group of non-irradiated mice. Eight basic hematological parameters of peripheral blood, bone marrow, spleen and thymus were studied. On day 4 after the irradiation with helium ions, the values of leukocyte counts in peripheral blood, bone marrow cellularity and spleen cellularity were reduced to about 10% of the respective control values while the decline after irradiation with gamma-rays amounted to about 50%. These and other results presented reflect a high relative biological effectiveness of 300 MeV/nucleon helium ions.

Institute of Biophysics Czechoslovak Academy of Sciences Brno Czech Republic

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