ABSTRACT The primary objective of Project 2.2 was to measure initial- and residual-gammaexposure rates as a function of time at various distances from high-yield-thermonuclear detonations. Secondary objectives were to measure the residual gamma~exposure rate at the lip of the crater from a high-yield, land-surface shot; and to field test a prototype thermal detector to be used in a radiological-defense-warning system. The residual-gamma radiation was detected by an unsaturated-ion chamber, whose output determined the frequency of pulses that were recorded on electro-sensitive paper. Most of the initial-gamma-radiation stations consisted of scintillation detectors whose output determined the frequency of pulses that were recorded on magneiic tape. Some initial-gamma instruments were similar to those used during Operation Castle. The exposure vate near the cruter was measured with a detector-tclemeter unit dropped from a helicopter. Residual-gamma-exposure rate versus time was obtained after Shots Zuni, Flathead, Navajo, and Tewa. The observed average-decay exponents for these events were 1.1 for Zuni and Tewa, 1.2 for Flathead, and 1.3 for Navajo. In some cases, the effect of rain- fall in leaching the activity decreased the exposure rate by a factor of two. Records from Shot Flathead at 7,730 fee: and from Shot Navajo at 13,870 feet indicated that at these locations about *h, of the total inttiul-gamma exposure was delivered after the arrival of the shock front. ‘The crater-lip measurements indicated that the method was a feasible one; however, “4 no usable data was obtained. The thermal-radiation detector responded satisfactority to a distance of 20 miles. detonation at a