TEST A: EXPLOSION IN AIR 



wavelength was roughly one ten-billionth of a centi- 

 meter; 25,000,000,000 such waves would be required 

 to cover one inch. The energies of the individual gamma 

 ray photons, being in exact inverse proportion to the 

 wavelength, were tremendous. A typical photon had 

 an energy of about one million electron volts. The high 

 energy of these photons meant that they had great 

 penetrating power — greater than that of typical X- 

 rays. In practical terms this meant that no ordinary 

 screen of steel, lead, or other material known to man 

 could successfully block off the radiation. Very heavy 

 steel walls, several inches thick, would reduce the in- 

 tensity by an appreciable factor and foot-thick steel 

 walls would reduce the intensity to a fraction of the 

 original value. But in the face of such extremely in- 

 tense radiation as that which struck the target ships, 

 even a fraction of the initial intensity might do serious 

 and lasting harm. 



To compute the total potential effectiveness of nu- 

 clear radiations on ships' crews has not proved to be 

 easy. To be fully meaningful, such computations must 

 take into account many factors. The most obvious of 

 these factors is the distance of the ship from the Zero- 

 lioint. All radiations are, of course, less intense at 

 greater distances and are therefore less effective there. 

 But the situation is complicated; the decrease in in- 

 tensity of some kinds of radiation is much more pro- 

 nounced than for others. Even fast and slow neutrons 

 show unlike deference to distance. Gamma rays too 



123 



