on a rocket. On occasion, devices were detonated underwater or buried in the earth. In theory, personnel could be exposed either by the radiation emitted at the time of explosion and for about 1 minute thereafter -- usually referred to as initial radiation -- or the radiation emitted later radiation). (residual In practice, however, there was no involuntary direct expo- sure of personnel to initial radiation during testing. This is part of the violent nuclear explosion process itself; close enough proximity for initial radiation exposure would place an observer within the area swept by lethal blast and heat waves. The neutron component of initial radiation did indirectly contribute to the possibility of personnel exposure. amounts by nuclear weapon explosions. Neutrons are emitted in large They have the property of altering certain nonradioactive materials so that they become radioactive. This process, called activation, works on some forms of sodium, silicon, calcium, manganese, and iron, as well as other common materials. The activa- tion products thus formed were added to the inventory of the radioactive products formed in the explosion Process. The radiation emitted by this inventory is referred to as residual radiation. The potential for personnel exposure to residual radiation was much more Of a real problem. In the nuclear explosion process, fissioning atoms of the heavy elements, uranium and plutonium, split into lighter elements, releasing energy. These lighter atoms are themselves radioactive and de- cay, forming another generation of descendants from the original fissions. This process is rapid immediately after the explosion but slows later and continues for years at very low levels of radioactivity. The overall radioactivity of all the fission products formed decays at a rate that is closely approximated by a rule that states that for each sevenfold increase in time the intensity of the radiation will decrease by a factor of ten. Thus, a radiation rate of 1 roentgen per hour 28 (R/hr) at