Analysis of radiation-induced acentric fragments in human G0 lymphocytes

Acentric fragments induced by low and medium LET radiations and observed in the first mitosis after stimulation were evaluated in the total collective of cells and in the sub-collectives of cells with and without dicentric chromosomes. For 13 MeV electrons and 150 kV X-rays the dose-yield relationships of all acentrics and of excess acentrics (acentrics not associated to dicentrics) were best fitted by linear-quadratic functions. For soft X-rays (10 kV) the dose-yield relationship of excess acentrics was linear. LET-independent proportions of, on the average, 1.03 +/- 0.07 acentric fragments associated with 1 dicentric chromosome and of approximately 0.5 acentrics associated with other aberrations of the binary interaction type have been observed. The linear yield components of the excess acentrics are relatively large, and an LET-dependent proportion, decreasing with increasing LET, exists between the liner components of excess acentrics and dicentrics. This may be taken to indicate the presence of acentrics resulting from single "primary lesions", a result questioning Revell's exchange hypothesis. The evaluated distributions of excess acentrics show overdispersion, which can be explained by the simultaneous formation of two acentrics in certain incomplete exchange aberrations of interstitial deletions.