Irradiation of Biological Materials by High Energy Roentgen Rays and Cathode Rays

Abstract

In this work roentgen rays and cathode rays of several million‐volts energy have been applied to an investigation of their biological, photo‐chemical, and germicidal effects, particularly as they are related to the processing of foods and biological materials. A constant‐potential electrostatic generator, together with an acceleration tube, was used to produce continuous streams of electrons with homo‐geneous and controllable energy. [R. J. Van de Graaff, K. T. Compton, and L. C. Van Atta, Phys. Rev. 43, 149 (1943).] These high energy electrons were utilized both for the production of penetrating roentgen rays and for the direct irradiation of materials. The mechanism of the biological action of both roentgen rays and cathode rays is discussed, as well as the energy considerations in their application to various absorbers. The companion paper [C. G. Dunn, W. L. Campbell, H. Fram, and A. Hutchins, J. App. Phys. 19, 605 (1948)] reports on measurements of the lethal action of these radiations on a wide variety of micro‐organisms and also on the effect of the radiations on enzymes, vitamins, and certain whole food products. Both investigations have been conducted cooperatively by the Departments of Electrical Engineering and Food Technology at the Massachusetts Institute of Technology. The systematic and quantitative study of the effects of roentgen and cathode rays on various elementary forms of living matter is regarded as an essential prelude to their possible widespread application to the preservation of foods and the sterilization of various biological materials. It was realized that the mechanisms of biological action of high energy roentgen rays and cathode rays are similar and depend closely upon the ionization energy absorbed per gram of material. The studies were begun with roentgen rays since these were immediately available and permitted quantitative measurement of the energy absorbed in the biological materials. Later, the water‐cooled gold x‐ray target was replaced with an aluminum cathode‐ray window, and corresponding studies were begun on the direct application of high energy electrons to these materials. During the period of these biological studies the x‐ray source was also used in a daily clinical program of deep cancer therapy under the medical direction of Dr. Richard Dresser and also in the investigation of the physical properties of high energy radiations. [R. Dresser, Radiology, in publication.]