CHAPTER 17 Iv, instead of dng, I inatead of Gyr I° instead of dy The computation of dhR in general involves three steps: (1) the calculation for radiation received from above (through the decks); (2) and (3) the radiation coming through the sides of the ship. In the present method, actual deck and bulkhead thicknesses measured from ship's plans are mitiplied by an empirical factor of 2 to take into account machinery and piping. The evaluation of the integrals of Eq. 17-23 for all the energies in the source spectra would be an exceedingly lengthy task, even when machine-computed. It has been found practicable to minimize computations by replacing the large mumber of energies (as many as 171) actually present with "pseudospectra" derived from the fission-product spectra.5’ ‘he pseudospectra for given times after fission and a given radiation-source configuration consist of only 5 energies: 0.25, 0.40, 0.75, 1.25, and 2.75 Mev. Each of these energies is weighted in such away for each time, as to give virtually the same attemation (absorption and scattering) as the more complex actual spectrum would give. The weighting fractions for the five (5) energies and for three (3) times after fission (70 sec., 1.12 hr, 23.8 hr) and for iron and air or water ere given in Ref. 57. The details of the theory and method of evaluating the integrals are presented in Ref. 53, along with the limitations of the results of the calculations. It is pointed out in Ref. 53 that the major limitations arise from the use of a buildup factor to account for the dose~rate contribution of photons scattered one or more times in the attenuating media before reaching their receiver. The calculations of unscattered flux are exact, but the calculations of scattered flux rely on the infinite-medium buildup fectors of Goldstein and Wilkins.52 These buildup factors are stated by the authors to be accurate, probably within + 10%. However, in this method of calculating ship-shielding factors, they are applied to finite media, and it is assumed that slabs that are actually separated (as ship decks) behave in the same way, with respect to attenuating ecattered radiations, as a single slab having the same total thickness. It is estimated that the errors in the slab calculations will be amall compared to the uncertainties and errors introduced in attempting to idealize the ship structure, the geometry, and the characteristics of the radiation sources. a re ee ne em ee ee mene