' 27), it would seem that formation of the precursor haslittle effect on the measured parame- ters. Little attempt was made at a thorough analysis of the measured data on the second shock (Figs. 28 and 29). Its formation is apparently unrelated either to formation of the precursor or to the type of surface over which the shock wave travels. It was noted that the peak pressures in the second shock dropped off much morerapidly than in the initial shock. 6 | RESULTS SCALED TO 1 KT AT SEA LEVEL Measured parameters on Mike and King shots have been scaled to 1 Kt (RC) at sea level; significant characteristics of the two shots and the scaling factors used are listed in Table 7. It was desired to compare scaled data on time of arrival and peak pressure vs distance with the composite curves prepared by the Naval Ordnance Laboratory (NOL) for Tumbler shots 1 to 4, in which these parameters were scaled’ to 1 and 2 Kt. Thus it was necessary also to scale the data on time of arrival to 20°C, the temperature used by NOL in preparing these ref- erence curves. Because no Scaled data on positive-phase duration and positive impulse were availabie, however, it was necessary to draw comparisons with scaled curves for 1- and 2-Kt bursts as derived'* from the IBM problem M for these parameters. Measured peak over- pressures are also compared with the height-of-burst curves for nuclear explosions published in TM 23-200.”° 6.1 Mike Shot Scaled values of the various parameters are presented in Table 8. This shot wasasur- face burst. Therefore, if none of the energy normally going into blast was lost to the surface, the scaled values would be those obtained from a burst of a 2-Kt bombin free air, i.e., froma bomb of twice theyield. As can be seen from Fig. 30, scaled arrival times correspond closely with those indicated by the composite curve for a 2-Kt bomb (evidently the scaled times of arrival fit the 2-Kt reference curve within the accuracy to which the yield is known). Because NOL did not make measurements of time of arrival at scaled distances greater than 1400 ft, however, it was necessary to extend the reference curves for 1 and 2 Kt by tying in curves based on measured results! from Tumbler shot 2. This application of data obtained by another group was deemed ,°* valid in view of the fact that beyond this scaled distance the shock velocities are essentially sonic velocities. Peak positive overpressures, plotted against scaled distances from zero (Fig. 31), are compared with the corresponding curves for 1 and 2 Kt as derived from Tumbler data at over- pressure levels ranging from 30 to 5 psi. At the lower overpressure levels the reference curves are essentially the Stoner-Bleakney curves as reproduced in SC-1827(Tr).*! Because the Stoner-Bleakney curves did not match exactly those published in WT-513 but were parallel to them, the curve for the lower overpressure levels was moved to the right far enough to obtain a continuous curve. Measured overpressures from Mike shot seem to fall on the 2-Kt curve in the higher overpressure range (12 to 20 psi) and follow a smooth transition toward the 1-Kt curve in the lower overpressure regions. It is believed that the point at 3.6 psi may be low because of faulty measurements. The fact that in the lower overpressure regions the measured points fall away from the 2-Kt curve is attributed to the effects of a nonhomogeneous atmosphere or atmospheric refraction. It is unfortunate that no pressures in excess of 20 psi were measured, for it would be interesting to see whether they fell-on the 2-Kt curve. Although it would have been preferable to have been able to evaluate scaled values of positive-phase duration and positive impulse against measured values of the same parameters as derived from data on other tests, lack of such data madeit infeasibie in this instance. However, when peak pressures and arrival times computed from the IBM problem M were compared with those obtained by Hartmann et al., they were found to be in agreement within rea- 50 age 49 Lelefed. a