Relative Effects of X-Rays and Neutrons on Chromosomes in Different Parts of the “Resting Stage”

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Abstract
1. The per cent normal anaphase chromosomes is a negative exponential function of the dose of neutrons or x-rays in different parts of the nuclear cycle. Chromosome abnormalities are, if allowance is made for multiple hits, therefore directly proportional to the dose at all stages studied. 2. The ratio of neutron to x-ray efficiency ([image]/x) is constant for different species at the onset of the prophase, but increases by a factor of at least 2 during the nuclear resting stage of single species. 3. Increase in [image]/x during the resting stage indicates Conditions for chromosomes response are not constant during resting stage. The intrachromosomal structure responding to ionization may be different for the different parts of the nuclear cycle and resting stage; a theory invoking a single mechanism for the production of chromosome abnormalities is not adequate. The relative effect of neutrons on chromosomes in the resting nucleus is greater than with x-rays. Neutron therapy may produce regression in tumors which do not respond to x-rays. The daily "safe dose" for exposure to neutrons may be considerably less than x-rays. 4. The use of neutrons and x-rays as described furnishes a method for identifying the functional stages which cannot otherwise be identified.

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