CHAPTER 17 2. Underwater Bursts. The Ref. tS method of predicting the deposit dose resulting from underwater bursts employs the same basic theory as that for predicting deposit dose from surface bursts, but defines the parameters differently. Times t; and ty are estimated from the base-surge dimensions and rate of motion. Such values mst be obtained from a base-surge model (see Vol. 1 of the Handbook). Fur- ther test data are required to determine whether deposit dose is significant for an underwater burst. 17.6.5 Theoretical Colculotions for Shielded Locations A computational method has been developed at NRDL”™ to calculate the effectiveness of a ship's structure in attenuating the gamma radiation from activity deposited on the weather deck. Results of the calculations, in terms of the shielding factor, can be obtained for any specific location within the ship. The method, essentially a means of calculating the value of the ratio of the dose rate at a given location within the ship to the dose rate at a given exterior location, is independent of the quantitative value of either dose rate. The NRDL computational method employs an idealized concept of the interactions of radiations with a ship's structure, and is based on several simplifying assumptions: (1) deck-deposited activity is a uniform distribution of isotropically emitting point sources on horizontal surfaces only; (2) buildup factors computed for infinite media are applicable for the finite shielding layers of a ship; (3) material in separate layers, like decks of a ship, has the same scattering char- acteristics as a single elab of the total thickness; (4) a deck-platingthickness miltiplying factor of 2 accounts for shielding material other than deck plating (bulkheads, beams, machinery, etc.); (5) pseudospectra, consisting of five energies, can be used in calculations to replace actual fission-product spectra for given times after fission, and can be weighted for each time to give virtually the same attenuation as the more complex actual spectrum would give. A brief discussion of the method followa; details of the method are given in Refs. 53 and 70. The theory was developed from the basic expression (Eq. 17-13 in 17.5.5) for the exposure dose rate dy (r/hr) at a distance x (cm) from a point isotropic source emitting 1 photon/sec, nis of energy E; in a homogeneous medium: d . “yx kuai nyEqBye a i” hax r/hr (17-13) The exposure dose rate due to a polyenergetic point source is found by summing the above equation over all the emitted energies. ; ; The on fase factor, as defined in Section 17.55, dose from both from unscattered is the 7atie of the scattered and unscattered radiations to radiations only. 4 “ the dose COPY BEST AVAILABLE 17-8) Se A OR Cm ee gee me eae et