provide the same shielding. Factors for converting circular salabe to equivalent rectangular slabs are presented graphically in Ref. 19. Further, it ie necessary to integrate cver the source region to find the exposure dose rate for any constant thicknees of absorber. It was found possible 53,55 to express the results of Goldstein and Wilkins for the dose buildup factor, B, of Eq.17-13, for any given medium and quantum energy, by an expression of the forn. B=) 1+ a(ux) + v(wer?| ec(ux) (17-19) The constants, a, b, and c may be related to the quantum energy E, and evaluated for various media. Values of the constants for buildup in dron and air or water are given in Ref.55, Table 2. An expression of the form of Eq.17-19 makes it possible to integrate over a source region, since the buildup factor has analytic form and the resulting expression is integrable. The integrated expression for exposure dose rate due to sources distributed in a volume of air or water beyond the surface of a circular sleb is given in Ref. 54. For simplicity of notation, the in- tegral forms will be used in the remainder of this discussion. Then the dose rate at an exposure point shielded from the volume source by a finite circular slab of radius R may be expressed: anR = do Be -(ux)' av lgxe (r/hr) (17-20) Explicit calculation of the dose rate at a shielded location in every case involves knowledge of the source strength, d,, a quantity that may not be known. However, the shielding effectiveness of the location is expressed in terms of an attenuation factor, or shielding factor, representing the ratio of dose rate at a shielded location to that at an unshielded location (epproximately over the exposure point and usually considered to be 3 ft above the slab (deck). In such ratios, the source strength, do, cancels. Although shielding factors do not provide actual dose or dose-rate values for below-decks locations, it ie frequently desirable to evaluate the shielding factor for a given location to determine the degree to which the ship's structure would attenuate transit radiation. The following ratios are used in practice to evaluate the shielding factor: REST AVAILABLE COPY 17-59