Comparative Effect of 200 KV. X-Rays and Gamma Rays on the Pupae of Drosophila Melanogaster: I. Determination of "Equivalent Roentgen" Value for Gamma Rays: II. Summation Experiments with X-Rays and Gamma Rays

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Abstract
I. Determination of “Equivalent Roentgen” Value for Gamma RaysThe roentgen has been adopted as the international unit of quantity or dose of x-rays and has proved satisfactory in practice. It is based on the measurement of ionization, satisfying the physical conditions of an “absolute” measurement. Since gamma rays also produce ionization, it is therefore theoretically possible to extend this unit to these rays as well, which for practical reasons is highly desirable.Direct and indirect methods of measurement have been applied for that purpose. The direct method involves the adaptation to the measurement of gamma rays of the same physical premises applied to the establishment of the international roentgen for x-rays and has been shown to be attended by considerable experimental difficulties, the analysis of which is beyond the scope of this report (see Failla and Marinelli, 1). The indirect method consists in a comparison of gamma ray doses of unknown roentgen value with x-ray doses of known roentgen value producing an equal effect on a test object. The dosage values thus obtained can be expressed in equivalent roentgens (Failla, 1933). It need not be emphasized that the unit of gamma ray dosage thus determined does not necessarily satisfy the conditions which the definition of the roentgen imposes. On the other hand, such a procedure gives the true comparative evaluation of the total secondary electronic effect and its biological effectiveness in a given object, which is the final determining factor for conditions met with in practice.

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