Goodhead D T, Thacker J, Cox R
Int J Radiat Biol Relat Stud Phys Chem Med. 1979 Aug;36(2):101-14. doi: 10.1080/09553007914550861.
Carbon K characteristic ultrasoft X-rays of energy 0.278 keV were found to be effective in inducing inactivation and mutation to thioguanine resistance in cultured V79 Chinese hamster 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 keV aluminium 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 carbon X-rays are found to be more effective than gamma-rays and are probably at least as effective as long tracks of helium ions of similar LET. These observations extend the conclusions previously drawn from the observed effectiveness of aluminium X-rays regarding the sizes of the subcellular sites involved in inactivation and mutation. They imply that the sensitive sites smaller than about 7 nm, and that highly localized energy depositions consisting of less than or approximately 14 ionizations are sufficient to produce biological effects. These results are also in contradiction to models of radiation action which require relatively large sites, such as the usual form of the 'theory of dual radiation action'.
人们发现，能量为0.278keV的碳K特征超软X射线能有效诱导培养的V79中国仓鼠细胞和人二倍体成纤维细胞发生失活和对硫代鸟嘌呤产生抗性的突变。这些X射线可作为细胞内敏感位点的探针，因为它们产生的低能光电子径迹范围约为7nm；这比先前研究中使用的1.5keV铝X射线产生的径迹小一个数量级。要对结果进行详细解释，需要对细胞内敏感位点的位置做出假设，但是，对于任何合理的假设组，发现碳X射线比γ射线更有效，并且可能至少与具有相似传能线密度的长径迹氦离子一样有效。这些观察结果扩展了先前从铝X射线的观察有效性得出的关于参与失活和突变的亚细胞位点大小的结论。它们意味着敏感位点小于约7nm，并且由少于或约14次电离组成的高度局部化能量沉积足以产生生物学效应。这些结果也与需要相对较大位点的辐射作用模型相矛盾，例如“双辐射作用理论”的通常形式。
