Supplementary Estimates of Radiation Geometry and Energy Response for Usnrdl Gamma-intensity-time Recorder (gitr) Model 103

Book excerpt: Estimates of radiation response are presented for the Model 103 Gamma-Intensity-Time Recorder (GITR) as used at Operation Sunbeam. The GITR detector unit, consisting of two concentric ionization chambers, was mounted inside the GITR recorder case and located 3 ft above ground level. GITR responses and their time-dependence were estimated for several idealized radiation source geometries and several calculated gamma energy spectra. Estimated response values are presented as fractions of the GITR's calibration-response to Cs137 radiation beamed at the top of the unmounted detector along its longitudinal axis. The principal conclusions drawn were that: The GITR responses to distributed sources with specified gamma energy spectra did not show a significant dependence upon the source geometries investigated. There were about 17% differences between the responses of the two concentric detectors. The responses changed about 15% during the first 100 hours after fission. The use of overall average GITR responses for distributed sources seems warranted; there is 95% confidence that 95% of the population of GITR responses will be within 12% of the overall average response of 1.16 for the high-range detector, and within 14% of the overall average response of 0.99 for the low-range detector, during the first 110 hours after fission. (Author).