Breakage of Human Interphase Chromosomes by Alpha Particles and X-rays

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Abstract
The technique of premature chromosome condensation (PCC) was used to compare the early formation of chromosome breaks in non-cycling HF19 human diploid fibroblasts when irradiated with slow alpha particles (3·2 MeV, 128 keV µm−1) or 250 kVp X-rays. For both radiations the production of PCC breaks increased approximately linearly with dose. The production coefficient for alpha particles was 12·5 ± 0·6 per cent per Gy and for X-rays it was 5·8 ± 0·2 per cell per Gy. Hence, the relative biological effectiveness (RBE) of the alpha particles was 2·16 ± 0·13. This is smaller than reported values of the RBE for the production of chromosome-type exchange aberrations by slow alpha particles. This implies that there is a difference, spatial or qualitative, in the initial breaks produced by the densely ionizing alpha particle tracks and the more sparsely ionizing electron tracks from the X-rays.