Operation UPSHOT-KNOTHOLE, Nevada Proving Grounds, March - June 1953. Project 29.4. Effective Energy of Residual Gamma Radiation. Report to the Test Director.
DEFENSE ATOMIC SUPPORT AGENCY WASHINGTON DC
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Evaluation of the gamma-ray quality of the residual radiation following an instantaneous fission reaction is necessary for establishing design requirements of radiation-detection instruments used in personnel monitoring. A theoretical study of the gamma-ray spectrum from fission products is described as a function of time from the fission reaction. The energy flux of photons with energy below 0.2 Mev increases relative so that of photons with higher energies as the time from fission reaction increases up to seven days. This increased relative flux of photons with energies below 0.2 Mev, together with a slight general decrease of photon energies due to Compton scattering in the air, can account for the relative variation of readings from energy-dependent detectors which were used in the field studies. Field measurements were obtained with energy-dependent ionization chambers, depth-dose curves in a phantom man, and photographic absorption curves made with copper spheres. These field measurements showed the presence of a wide range of photon energies from around 60 kev to above 600 kev.