Scientists and military planners assigned to devise defenses against nuclear blasts have had their hands full.
They must shield prospective targets against thunderous shock waves, searing heat, deadly X rays, gamma rays and neutrons. They must also guard against a lesser-known product of atomic explosions called electromagnetic pulse, or EMP. In a recent Washington speech, Senator Henry Jackson, atomic-weapons specialist of the Armed Services Committee, insisted that despite five years of research, EMP still poses a "serious problem" to the nation's communications, radar and missile systems.
EMP is created when gamma rays from an exploding weapon strike electrons in the surrounding...