The Relative Effects of X-Rays, Gamma Rays and Beta Rays on Chromosomal Breakage in Tradescantia.

OR some time it has been generally considered that the production of F chromosomal aberrations in Tradescantia and many other materials is essentially independent of the wave length of the exciting radiation in the region shorter than 1.5 A. This view has not been seriously questioned in recent years and to date has remained one of the fundamental tenets of radiobiology. A number of isolated instances have been noted in this laboratory in which the effects of 250 kvp X-rays and mixed 1.17 and 1.33 Mev y-rays from Cos0 did not conform to this expected biological equivalence. In the course of, a series of experiments on the relative effects of Co60 y-rays and P32 /3-rays on Tradescantia, we have extended our measurements to include a comparison in the X-ray region. A considerable difference between the effects of X-rays and CoS0 y-rays or P32 p-rays has been observed. In quantitative radiobiological work of this type, precise and reliable physical dosimetry is a major requirement. For this reason the physical methods used have been described in somewhat more detail than is customary. Due in large part to the continuing program carried out in this laboratory f,or the past three years on the standardization and calibration of our X-, yand p-ray sources, any errors in our absolute radiation measurements should be less than 5 percent.