tion on the interior of the fireball by a layer of NO, near the surface. Even apart from these arguments, the opacity of soil is high, so that the temperature mustfall off extremely rapidly into the soil. The Heat capacity of the soil itself provides a blanketing layer which is cool enough to shield the surface from high-fre- quency radiation on the interior of the bomb. From these considerations we do not believe that soil vaporization is a material factor to crater formation for nuclear explosions over soil. 0.60 eral conclusions regarding the shape of craters for nuclear explosions from the preceding discussion. A starting point for the discussion of scaling might be similarity scaling, but, without the risk of assumingit, crude similarity was obtained as a derived result in Fig. 8 of LA-1529 for the theoretical comparison of Greenhouse George shot and the Operation Ivy Mike shot. By simi- larity, it is meant here that the same pressure would occur at a depth in soil on Mike which is roughly related as the cube root of the yield Sse 0.50 Et 0.30 Way RELATIVE IMPULSE 0.40 0.20 0.10 0 Fig. 1.6 10 20 30 50 60 40 HORIZONTAL DISTANCE, YO 70 80 90 Relative Impulse vs Horizontal Distance. Theoretical calculation derived from Fig. 1.2. Note approximate linear delay of impulse with distance, which woud probably become negligible near 200 yd. t Figure 1.2 is used to measurethe relative impulse ag a function of horizontal distance, and these results are plotted in Fig. 1.6. A striking result of this graph is the linear decay of relative impulse as a function of horizontal distance. Note that the impulse would be relatively small if extrapolated to distances like 600 ft. 1.3.4 Scaling of Craters for Nuclear Explosions Despite the inherent fluctuations in soil constants, it appears possible to draw some gen- ratio to the corresponding depth on George. The difference between a surface shot and a tower shot is less than might be expected at first because the shock velocities in air are so much greater than the shock velocities in soil; the shock from a surface burst will have traveled only a few feet in soil by the same time the incident shock in air would have reached the ground from a tower shot. On the relatively long time scale involved in the propagation of shocks in soil, both a surface shot and a tower shot can probably be considered surface shots so far as the ground is concerned. [%