Document qKpNYKeYDe49kyKZpnakp0BM

716 LEON F. CURTISS or a suitable filter, transparent to visible light but sufficiently opaque to x-ra$ may be placed in the line of sight. j Since many electrical shocks prove fatal only because of failure to ap restorative treatment at once, it is imperative that all personnel concerned wt the operation of an x-ray unit be familiar with the methods of artificial resp|| tion and the aftertreatment of a revived person. This familiarity should bbai result of actual training. Although a physician should be summoned at .;0" the restorative measures should be started immediately, since the chance ' a successful outcome are greatly increased by appropriate procedures in* first few minutes after the shock. S. Shielding Materials for Protection against X-rays and Gamma Rays1 \ if; Singer, Wyckoff, and Day8 have made careful measurements on the relf thicknesses of lead, concrete, and steel required for protection from a narrow be of x-rays generated by potentials from 200 to 1400 kv. They found that foritf kv. the ratio of thickness of concrete to the thickness of lead to produce*1 same attenuation is 5.6, a relation that is strictly linear from 10 to 75 c concrete. At 10Q0 kv. this ratio is 6.4 for a range of thickness of concrete frb to 65 cm., with small departure from linearity in the region between 10 and 2( At 600 kv. this ratio has increased to 10 for a range of 10 to 50 cm. of conf and at 200 kv. the ratio is about 50 between 10 and 25 cm. of concrete. The ratio of thickness of steel to thickness of lead was found to varylff about 13.5 for 200 kv. radiation to about 1.5 for 1400 kv. radiation. For many purposes, lead is most suitable for use in screening x-rays. Ipf situations, however, it is more convenient and economical to use other including the structural materials of the building itself. One of the most CoS; is concrete, carefully compounded and poured to prevent formation of air8 It is usual to'specify lead equivalence of such materials to indicate their rL efficiency as a screen. The protection coefficient, which is the ratio of the'iMi ness of lead to the thickness of material that absorbs a given beam of radi' to the same extent, is more convenient for calculation. The lead equivalent a material is the thickness of lead found by multiplying a given thickness'^, material by its protection coefficient. Values for protection coefficients, takeigjf data by Kaye6 and his associates, are given in Table 5. _ ______ -.iri&k When dealing with x-radiation generated at potentials ab6ves;>200Vjljv scattering of the radiation is appreciable. At about 500 kv. the scfttteJSi'^M; tion has a hardness of about one half that voltage, an'd for 1000 kv. the>ij"|| is one third. Therefore, in computing thicknesses of shielding material-`'v -scattered--radiation--may--be-in-volved7-the--absorption-coefficients--foMe-raygw voltages corresponding to those for the scattered radiation must be used * *G. Singer, H. O. Wyckoff, and F. H. Day, J. Research Natl. Bur. Standards 38* (1847). % G. Kaye, W. Binks, and G. E. Bell, Brit. J. Radiol, 11, 676 (1938). y- RADIANT ENERGY 717 TABLE 6 & Protection Coefficients (with Reference to Lead) for Some Structural Materials ...... uilding aterial 150 kv. X-rays 200 kv. 300 kv. 400 kv. Gamma rays 0.08 0.013 0.0009 0.07 0.014 0.009 0.11 0.026 0.015 0.14 0.033 0.019 0.47 0.14 0.08 4. Shield of the X-ray Tube x-ray tube in all cases should be completely surrounded, except for the ening for the emergent beam, with protective material of adequate thickness jluCe the radiation to tolerance level or below at all points outside the beam ;lyJto be 'occupied by personnel. There has been a decided tendency in recent arlun the part of manufacturers to make this shield an integral part of the efpructure, or support. However, it is desirable to make certain that the Ming is adequate in all such types of tubes. Table 6 shows minimum lead ffiHUpses required for shields for a few typical voltages applied to the x-ray TABLE 6 Approximate Lead Thickness Required to Protect Individuals from X-rays Generated by Various Voltages Minimum required thickness of lead barrier (mm.) X-rays generated by peak voltages not in excess of (kv.) Minimum required - thickness of lead barrier (mm.) 400 500 600 800 1000 2000 5000 16.0 22.0 34.0 40.0 80.0 176.0 290.0 I-Kese values are only approximate to illustrate the nature of the problem. Actual installation the effectiveness of the shield should be tested by ^fluents of the dosage in roentgens at appropriate locations'lii'the vicinity -For safest operation-,--personnel-should never remain-unnecessarilv jicinity of an x-ray tube in operation, even though measurements have hifthiat the shielding meets the usual requirements. In most industrial itibns there is no reason for anyone to be near the x-ray tube during an