DNA 1240H-2 after making appropriate corrections, subtracting the deposit dose (dose accumlated after fallout started) from the GITR records. ever, such results must be considered speculative. 2. Underwater Bursts How- PF AS MA; BEST AY ATLA TLS COPY Transit radiation data available for underwater burete are from the four low-kiloton shots listed in Table 17-2. The magnitudes of the measured transit doses were significant in all four cases. Furthermore, the data indicate that the significance of transit radtation as a contaminating mechanism may be associated with the phase At Operation of the bubble when it breaks trhrough the surface. Crossroads, Shot Baker, the shallow burst that produced a broad column and mushroom cloud, the deposited activity from the rainout or fallout, ‘Yather than transit radiation, was the mejor source of contamination. However, there was practically no fallout from any of the ot three deeper bursts, and in each of those three tests the transit mation was the source of the gamma doses measured on the target ships. Avail- able data are’summarized in the following paragraghs. ‘Operation Crossroads, Shot Baker: A few dose-rate histories were recorded at Shot Baker,44,4,40and are estimated to be partly due to transit radiation. References +4and45 reproduce time-dose-rate records from four of the target ships. Examination of those records indicates that significant gamma doses were delivered during the times the ships were enveloped by the base surge. For instance, during envelopment by the base surge, peak dose rates of about 3500 r/hr, 180 r/hr, and 150 r/hr were recorded on LCT 874 (2420 yd from surface zero and slightly downwind) on APA 77 (USS CRITTENDEN, 1500 yd from surface zero and slightly downwind), and on ICI 332 (1890 yd from surface zero and elightly upwind), respectively. However, the departure of the surge caused no noticeable decrease in the dose-rate curves. Furthermore, on LCI 332 although the dose rate increased from about 50 r/hr to about 150 r/hr during en- velopment by the base surge between 2 and 5.6 min, the dose rate suddenly increased to about 870 r/hr at 7 min when the surge was about 300 yd downwind from the ship. According to Ref. 29, at weather deck locations, it was "estimated that 50 percent of the total dose was radfated from the mist during the time in which the vessels were engulfed by the mist,"and the same study gives a contour map of transit-rad- tation doses, obtained by subtracting deposit doses (computed by means of fallout collections) from total doses (measured by film badges). ration Hardtack: The two underwater bursts of this oper- ation (Shots Umbrella and Wahoo) provide the best transit-radiation records of any weapons test, and results indicate that exposure to the base surge of a shallow or moderately-deep underwater burst can result in high doses within the first 15 to 30 min. Dose-rate histories were recorded*? aboard the three DD's and the EC-2 at shots Umbrelle and 17-36