RADIATION UNITS

BACKGROUND

a. Although radioactivity was discovered in the late 19th century, it was originally considered a scientific curiosity with little practical value. During this time researchers discussed findings in terms of the effects of radiation or in terms of the type of equipment used in a particular experiment. For example, an experimenter might describe the type of x-ray tube and voltage used or he might describe the effects on the skin of a man exposed to radiation. A widely used unit was the so-called erythema dose--the amount of radiation which could cause an abnormal redness of the skin due to capillary congestion.

b. As experiments became more precise, and the experimenters became aware of the effects of radiation upon living tissue, the need arose for an accurate unit to enable comparison among the various types of x-ray machines that had proliferated during World War I. Experience gained in the war also showed the need for a careful study of the effects of radiation on personnel; such a study would require a standard unit for evaluating radiation doses.

c. For these reasons, the International Commission for Radiological Protection (ICRP) was formed. Meeting in Geneva, Switzerland, in 1925 and again in 1928, the ICRP recognized this need. The search for a suitable unit culminated in 1932 in the adoption of the term "roentgen."