Mutagenic and transforming effects of soft-X-rays with resonance energy of phosphorus K-absorption edge.

Syrian golden hamster embryo (SHE) cells were exposed to synchrotron-produced monochromatic X-rays at 5.747 (2.159 keV), 5.763 (2.153 keV) and 5.779 A (2.147 keV). Although X-rays of all wavelengths induced mutations and chromatid aberrations in a dose-dependent manner, when cells were irradiated with 2.153 keV X-rays, which correspond to the resonance energy of the phosphorus K-absorption edge, the frequencies of mutation and chromatid aberration at equal dose levels were higher than for X-rays of the other wavelengths. At equal survival levels, however, there was no difference in the frequencies of mutations and chromatid aberrations in cells irradiated with soft X-rays. On the other hand, the frequency of morphological transformation in cells irradiated with 2.147 keV X-rays was higher than those irradiated with 2.153 keV and 2.159 keV X-rays. The relative biological effectiveness compared to cobalt-60 gamma-rays in morphological transformation was 2.8 for 2.147 keV, 1.1 for 2.159 keV and 1.0 for 2.153 keV at a 37% survival level.