CHAPTER 17 17.6.6 Simulant Experiments An experiment was conducted on a Naval ship to evaluate shielding effectiveness of the ship's structure against gamma radiation from an external source. Results are reported tn Refs. 71,72,73,74 and 75. In the experiment, to approximate a condition of uniform contamination, a 145-curie Co™ source (1.25 Mev gamma energy) was pumped through plastic tubing laid out on the flight deck of the COWPENS (AVT 1), a light aircraft carrier. Two dosimeters were placed at each of various locations on the flight deck and in below-decks spaces. Numerous dosimeter readings were averaged and then divided by exposure time to provide dose rate as a function of time from the centerline of the ship. The measured flight-deck dose rates were corrected for the size of the “contaminated” area, since experimental data and computations indicated that the observed dose rate on deck would be increased by 4.5% if the entire deck were contaminated. Adjusted readings were used to determine the shielding factors. Two portions of the ship, designated A and B, were investigated. The A section had more and smaller compartments than the B section. Figure 17-16 illustrates echematic cross-sections of the COWPENS at the frames where the measurements were obtained. Measurements on the Gallery Deck, the Forecastle, and the Main Deck were made about frame 35 (the A Section), while measurements on the Hangar Deck and the 2nd and 3rd Decks were made about frame 85 (the B section). Dos- imeter arrays at each location were supported 3.5 ft above the various decks. The shielding factors obtained experimentally are listed in Table 17-5. Also listed in the Table, for the same locations and source energy, are shielding factors calculated by the theoretical method described in 17.65, above each location. using twice the total deck-plating thickness The factor of 2 was derived from measurements made in the B section. © Experimental results indicated that on large ships, such es eair- craft carriers, at locations on the 2nd and 3rd Decke and below, the ship's structure attemated radiations to less than 1% of the level on the weather deck. 17.6.7 Summary A eurvey has been made of available information on the interaction of surface ships with deposit radiation resulting from water-surface or underwater bursts. Results of the survey, which included weapons test data, experimental data using similants, and theoretical calculations, are mimmarized in the following paragraphs. BEST AVAILASLE COPY, 17-85 rene ee eee er er ee