Chopter / INTRODUCTION 1.1 OBJECTIVES The primary objectives of Project 2.2 were: (1) to measure the initial-gamma-exposure rate as a function of time from the detonation of high-yield-thermonuclear devices; and (2) to measure the residual-gamma-exposure rate as a function of time at land fallout stations. Secondary objectives were: (L) to measure residual radiation at early times on the crater lip of a high-yield, land-surface shot; and (2) to field test a prototype thermalradiation detector to be used in a radiological-defense-warning system. 1.2 BACKGROUND Los Alamos Scientific Laboratory (LASL) measured initial-gamma-exposure rate versus time for high-yield devices during Operation Ivy (Reference 1). It was found that high-yicld devices did not follow the relatively simple scaling laws of low-yield devices. Gamma radiation at 2 particular distance scales linearly with yield for devices up to about 100 kt. For megaton-range devices, gamma radiation scales higher with increasing yield. This enhancement of initial-gamma radiation was attributed largely to the hydrodynamic effect (Section 1.3.4). U.S. Army Signal Research and Development Laboratory (USASRDL) obtained several gamma-cxposure-rate~versus-time data points from high-yield devices during Operation Castle (Reference 2). The data obtained by USASRDL were lowerby a factor of 10 or more than the Super-Effects Handbook predictions (Reference 3). One of the purposes of Project 2.2 was to resolve the initial-gamma-radiation-scaling laws for high-yield devices. Of particular interest was a high-yield air burst, since it would allow correlation of the hydrodynamic effect from an airburst with that from a surface burst, USASRDL made measurements of residual-gamma-exposure rates from high-yield devices during Operation Custte (Reference 2). Only limited data were obtained because of a high loss of instruments eurly in the operation. These data indicated that the decay exponent fur the residua! activity varied with the type of nuclear device. Another purpose of Project 2.4 was to determine accurate decay exponents for residual activity. The thermal-radiation detector, part of an early-warning system for nuclear detonations, wat .ested with !ow~yield devices during Operation Teapot (Reference 4). ‘The tests were successfui. The detector showed a capability far in excess of the requirements. It was decided to determine the response of this detector to megaton-range devices during Operation Redwing in order to complete the testing. 1.3 THEORY The gamma radiation emitted from a nuclear detonation may be divided into two por-