3.2 ALTITUDE ABSORPTION MEASUREMENTS Data on radiation versus altitude, over land, are summarized in Table 3.1. Scintameter survey meters were used for the measurements during helicopter missions. A Top Hat radiation detector and a scintameter were used in the P2V-5 aircraft. The differences in the absolute values of the readings in the P2V-5 are due to the difference T rPryyrt T TUT TT Et (00 T 87 pct of Calibrations 3 o£ | Radiation , mr/hr Fell Within These Limits L L / } i! He 4 i] id! All Calibrations Were Within These Limits TTT — 0.0! fy 0.007 0.2 _t 0.4 41 0.6 t 0.8 _ 1.0 L 2 Reading , milliamperes Figure 3.1 Summary of 37 pre- and postflight calibrations of Top Hat radiation detectors. in the energy response of the two types of detectors. The scintameter, TH-3, uses a sodium iodide phosphor, which is more sensitive to soft gamma radiation. The Top Hat detector uses a plastic phosphor and has a response that is nearly energy-independent. The response of the two types of instruments is summarized in Figure B.2. Because fresh fission products have a 25