Appendix C CALIBRATION AND RESPONSE This appendix contains a mare detailed description of all calibration procedures and response factors used by the project. Some of this material appears in separate reports but has been gathered together here for greater convenience. C.1 STANDARD GITR CALIBRATION AND RESPONSE All GITR detectors were calibrated at NRDL with Co® sources standardized to within 3 per- cent. Calibration was performed with the detector in a standard orientation, the longitudinal axis of the detector and the beam parallel with the electrometer housing facing away from the source (source at 0°). The energy response of the detectors was determined at NRDL, using Co®’ and Cs!*" sources and broad-beam X-rays with effective energies of 180, 120, 70, and 35 kev. The response is uniform within 10 percent from approximately 100 kev to 2 Mev when the detector is surrounded by 0.13 inch of aluminum (Figure C.1). The directional response of the detectors was also determined by using these sources. Typical directional responses for the std-GITR and the UW- GITR are reproduced in Figures C.2 and C.3 for rotation about an axis orthogonal to the longitudinal axis of detector. response. Rotation about the longitudinal axis produces a completely uniform Optimum reliability and accuracy was assured by recalibrating each detector before and after each shot with a 120-curie Cs'" source installed in a trailer specially designed for the purpose. This source was standardized to the Co’ sources by means of a Victoreen 70-A R-meter and various calibrated chambers. Maximum reproducibility was assured by using a jig that exactly positioned each detector in the calibration beam in a radiation field of 57.0 r/hr. The calibration radiation pulse output of the detector was then adjusted to a period of 0.016 and 15.5 seconds for the low-range and the high-range channels, respectively. The low-range period of 0.016 second (instead of 0.0155 second) compensated for the 0.5-msec recycling time of the detector electrom- eter circuit. The calibration field was too low to permit a similar compensation for the highrange chamber. All calibrations are estimated to be accurate within 5 percent for the period of use between preshot and postshot calibration. C.2 ASEL-GITR CALIBRATION AND RESPONSE The directional response of the ASEL detectors was determined at NRDL, using an X-ray beam that peaks at 120 kev. The corrected output af the X-ray was 2,100 r/hr, and the precise energy of the 120-kev beam is given in Figure C.1. Typical directional responses for rotation about and orthogonal to the longitudinal axis of the high- and low-range ASEL detectors are presented in Figures C.4 through C.7. The basic calibration and energy response of each detector was determined at ASEL. A typical energy response for the ASEL detector is given in Figure C.8. The dose rate response from 40 r/hr to 10’ r/hr was determined for all detectors, using X-ray and Van de-Graaf sources. At EPG, the lower range of these dose rate responses was rechecked for all detectors on 2 May and again on 22 May, using a 200-curie Co" source with a 15° beam. This source produced a maximum field sufficiently uniform for calibration to 8,000 r/hr. A typical dose rate calibration curve for a high-range detector is reproduced in Figure C.9. The radiation pulse data 366