oA 1740-7 Eo (Mev/photon). The procedure ‘'s as follows: eo Be7 (Hx) ' inxs tha = KuagnE, av r/hr (17-16) where nE, tt Qo the source strength in units of Mev/cm3-sec and x = distance (cm) from the exposure point to the incremental element of volume, dV (ux)' = u)x,4px, where x) is the path length in air, xp 1s the path length in the slab, and each uy, is the total linear absorption coefficient for the corresponding medium. B «8B fe, (ux) '] is the dose build up factor, as defined for Equation 17-13. Further, do, a symbolic dose-rate meusure of source strength may be written: z do = KugnE, r/hr-cm (17-17) Note the difference ir units for do from a volume source (Eq. 17-17), and from a point rource (Eq.17-14). When the concept is used for a plane source in 17.45, dg will have the units r/nr. This results from a difference in the significance of n, which has the units photons, phgsane and photons respectively. eme-sec Bec (See also footnote after cm -sec © Equation 17-27, Section 17. 6.4.) Then the exposure dose rate at the exposure point shielded by a 6lab of infinite radius is defined by: Ghee = tof However, Ss av r/hr ships are not infinite in extent. (17-18) The slab of shielding represents a ship's structure above the exposure point, and, in general, is composed of a number of slabs of different sizes and thicknesses (corresponding to a ship's decks and piating and determined by the location of the exposure point). Therefore, the slab must be bounded, and for the idealized conditions of the problem, the individual slabs are considered contiguous and are treated as a single whose total thickness equals the sum of the thicknesses of the individual slabs. Although the shielding slabs are rectanrular, it was found more feasible to calculate the shielding effectiveness in terms of circular slabs that BEST AVAILABLE COPY 17-58 aoe ee - ~ oe ee ee : ee ee eee ee ee