The Economic Features of X-Ray Protection

Abstract

I.—Introduction PROTECTION against undesired exposure to x-rays or the gamma rays from radium can be had, but for economy and convenience it is desirable to analyze closely, with certain fundamental principles in view, each particular problem. Basic rules for x-ray and radium protection have been promulgated by the International Commission on X-ray and Radium Protection and published in numerous journals. More detailed rules, prepared in this country, are available in N.B.S. Handbook 20 (X-ray Protection) and N.B.S. Handbook 23 (Radium Protection). Reference to these is recommended before planning new x-ray installation. The handbook on x-ray protection gives the rules for maximum protection; if followed strictly, any errors will be on the safe side, though not necessarily the most economical one. We give, in these discussions, certain qualifications which may permit a more economical disposition of protective barriers and devices. At the same time a number of miscellaneous points requiring special emphasis are considered. II.—Tolerance Dose The so-called “tolerance dose” is the total x-ray energy that a person may receive continuously without suffering any damage to the blood or reproductive organs. This is expressed best in roentgens or in terms of an erythema dose. The tolerance dose recommended by the International Protection Commission is taken as a seven-hour daily exposure at a dosage rate not exceeding 10−5 roentgens per second. This is roughly 104 times the dosage rate of cosmic radiation. It is argued by the geneticists, based largely on the work of Mueller (3), that this is ten times the safe dosage; or, in other words, the tolerance dosage rate should not exceed 10−5 r∕sec. Their figure is based on the elimination of any second-generation genetic effects, whereas the accepted figure of 10−5 r∕sec. is based on the effect upon the recipient of the radiation only. As may be seen below, the radiation dosage rate may be reduced from 10−5 to 10−6 r∕sec. by the addition of, roughly, 30 per cent more lead in a given protective barrier. However, since the value of 10−5 r∕sec. is the present accepted tolerance dosage rate, all of our calculations will be based on this figure, and a discussion of the relative merits of the two values will not be entered into. Although genetic effects were not a consideration during the preparation of the international safety recommendations, it is possible that such a wide margin of safety has been provided that they have hitherto successfully protected against genetic mutations. III.—Lead Protective Barriers Since lead has the highest atomic number of any material readily available and easily worked, it is generally used for protective barriers and the protective value of other materials is referred to lead as a base.