Ionizing radiation and its chemical effects : a historical study of chemical dosimetry (1902-1962) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6q182n64p

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  • Chemical dosimetry developed in response to needs created by developments in the field of high-energy radiation. Shortly after the discovery of X-rays in 1895 and of radioactivity in 1896, the deleterious effects of ionizing radiation were recognized. To guard against the injurious effects of radiation in medical application, dose-measuring methods were considered necessary. The early dosimetric methods were based on what at the time were taken to be the chemical effects of ionizing radiation. In 1902, Guido Holzknecht (1872-1931), a Viennese physician, suggested a method of dosimetry which was based on the coloration of a salt due to irradiation. His proposal, the first of its kind, was followed within about five years by a number of others which were made by other physicians and radiologists and which were based on some visible chemical change. Subsequent developments in chemical dosimetry until about 1915 were concerned mainly with the calibrated scales used to relate the chemical change to dose, the problem being a lack of a radiation unit of dose. Further investigations of chemical systems for dosimetry were not made, however, until in the 1920's. In the meantime ionization methods of dosimetry became popular, although some of the earlier proposed chemical dosimeters were widely in use. The renewal of interest in the chemical effects of ionizing radiation in the 1920's stemmed from the extensive radiobiological research that was conducted owing to the expanded application of higher-energy X-ray units in medicine and in industry. From the research done to understand better the mechanisms underlying biochemical processes, there proceeded several dosimetric systems. The one that proved most reliable was the ferrous sulfate system recommended in 1927 by the biophysicist Hugo Fricke (b. 1892). This renewed research on the chemical effects of ionizing radiation also made some significant contributions for future developments in chemical dosimetry. Most fundamental, both to the developing theories of radiation chemistry as well as to the formulation of many dosimetric systems in the post-World War II period, was the observation made by Fricke and associates that the primary action of the radiation was on the solvent rather than the solute. The discovery of the neutron and of artificial radioactivity and the development of accelerating devices in the 1930's provided for still further application of ionizing radiation in medicine and in industry which increased the number of persons whose occupation was a source of radiation exposure. A growing concern for the protection of personnel contributed to attempts at standardizing dosage measurements. Although formal standardization began in 1928 when the roentgen was officially defined as a radiation unit by the International Commission on Radiological Units, it was not until 1962 that the rad was officially restricted as a unit of dose and the roentgen as a unit of exposure. The precision of the terminology contributed to more reliable dosimetry. The development of reactor technology in the 1940's gave rise to new problems in radiation protection. To monitor the mixed radiation fields present in the vicinity of nuclear reactors, film badges had to be modified for the detection of various forms of radiation. Also, various filter assemblies were introduced into the badge to reduce the energy dependence of photographic emulsions, thus to improve the accuracy of the film dosimeter. Research in radiation chemistry and in nuclear technology in the post-war period called for dosimetric methods useful over a wide range of dosage and not necessarily as sensitive as those required by research in medicine and radiobiology. As a result, chemical dosimetric systems effective over a range from about 10 to 10¹⁰ rads were made available. Although many of the systems were formulated on the basis of the indirect action of the radiation on the solute via the solvent, not every system had a comparable reliability nor did each meet all the requirements desirable of a dosimetric system.
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