Effectiveness of 0.3 keV carbon ultrasoft X-rays for the inactivation and mutation of cultured mammalian cells
Goodhead, D.T.; Thacker, J.; Cox, R.
International Journal of Radiation Biology and Related Studies in Physics Chemistry and Medicine 36(2): 101-114
1979
ISSN/ISBN: 0020-7616 PMID: 315385 Document Number: 144940
Carbon K characteristic ultrasoft X-rays of energy 0.278 ke V were effective in inducing inactivation and mutation to thioguanine resistance in cultured Chinese hamster lung V79 cells and human diploid fibroblasts. These X-rays act as a probe of the sensitive sites within the cells since they produce low-energy photoelectron tracks of range about 7 nm; this is an order of magnitude smaller than those produced by the 1.5 ke V Al X-rays used in previous studies. A detailed interpretation of the results requires assumptions to be made about the positions of the sensitive sites within the cells but, for any reasonable set of assumptions, the C X-rays were more effective than .gamma.-rays and were probably at least as effective as long tracks of He ions of similar LET . Conclusions previously drawn from the observed effectiveness of Al X-rays regarding the sizes of the subcellular sites involved in inactivation and mutation are extended. The sensitive sites are apparently smaller than about 7 nm and highly localized energy depositions consisting of .ltorsim. 14 ionizations are apparently sufficient to produce biological effects. Models of radiation action which require relatively large sites, such as the usual form of the theory of dual radiation action, are contradicted.