Radiofrequency energy produced by the explosion can be detected by radio receivers and, with the addition of filtering and processing circuitry, can also provide information about the energy flow from the explosion. Such measurements permit remote placement of receiving and recording instruments. Preshot preparation included the hazards normally associated with heavy construction, and some exposures of workers to radiation occurred in areas contaminated by earlier tests. The potential for radiation exposure of personnel associated with weapon diagnostic experiments depended upon the proximity of the measurement or data recovery point to ground zero and the time lapse between the detonation and the data collection. The primary radiation exposure potential is from fission* products and Materials made radioactive by neutron activation of device and Earth materials in the vicinity of ground zero. Thus, the distance from ground zero is a principal factor in assessing exposure to persons engaged in the experimental program. Since radioactive material decays with time, the time lapse between the explosion and exposure is a critical factor in dose assessment. Pri- Mary recording media for these experiments were photographic films from oscilloscope, streak, or framing cameras located in survivable bunkers near the detonation point. Because radiation fogs film in time, these films and other time-sensitive data were removed from the bunkers by helicopter-borne personnel within hours of the detonation to minimize damage by fogging. This recovery constituted the main potential for ex- posure of weapon diagnostics participants. * Although the CASTLE devices were thermonuclear, or fusion, devices, a significant portion of their energy release resulted from fission processes. 34