A Method for the Study of Scattered and Secondary Radiation in X-Ray and Radium Laboratories

THE question of the exposure to radiation of workers with X-rays or radium is generally recognized as very important. It is known that the effect of radiation is cumulative, to a certain extent. The amount received at any given time may be small, but the more or less continuous exposure to such small quantities may presumably in time produce a very serious effect. This radiation does not, in general, come mainly from the primary source,—the X-ray tube or radium applicator. It is the scattered and secondary radiation from walls, floors, and other solid objects which must be guarded against, because it is less obvious, and from such radiation it is harder to shield oneself. It would be very desirable to know (1) how much radiation an individual can receive without harmful effects, and (2) how much any given individual is receiving. In order to ascertain these points, it is necessary to devise a method of measuring quantitatively the amount of radiation being received by any worker. When this is done, the first question can be answered by a study of the condition of many X-ray and radium technicians who have been exposed for a considerable time. The usual method of investigating the scattered and secondary radiation in a given place is to expose dental films for some days or weeks. If a film shows considerable darkening in a short time, it is evident that there is an undesirable amount of radiation. Pfahler (1) examined films carried by several hundred workers in different parts of the country, and evaluated the method. It is qualitative, or, at best, roughly quantitative, in the absence of a means for measuring accurately the darkening of the film and comparing it with standards. An attempt to get quantitative results has been made by Mutscheller (2) using an ionization method. Such a method has the advantage that the measurements are quickly and easily made. But the electroscope must be calibrated to read in terms of the chosen unit, which is not simple. Moreover, the readings are not continuous nor additive, and the amount of radiation received must be calculated from a number of isolated measurements. The radiation to be measured, however, is apt to vary considerably from time to time, and an accurate measurement of one hour's or even one week's output may give false ideas as to the quantity received over a long period of time. Furthermore, measurements in one or several definite parts of a room do not adequately represent the exposure of the technician. An X-ray film, worn or carried by the worker, gives a cumulative record of the radiation it receives. If this record can be translated, it is preferable to one consisting of intermittent measurements. Repeated tests of this sort will give accurate information regarding the radiation received by any one worker.