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 outside the controlled conditions of the laboratory on the ship housing the radiation safety organization. Therefore, the only expedient way to estimate alpha radiation was to assume that some relatively stable ratio existed between alpha emitters and gamma or beta emitters. One could then measure gamma or beta radiation and calculate the alpha hazard. As beta and gamma radiation decreased, however, alpha radiation remained because of the long decay time of the plutonium and other alpha emitters.

EFFECTS EXPERIMENTS

Central to the test series was the experimental program. This program and its requirements dictated the form of the test organization and the detail of personnel participation. CROSSROADS had two experimental programs. The first was to determine the effects of nuclear detonations on animals and on military equipment such as ships, aircraft, and various supplies. The second program was to measure weapon phenomena such as heat, blast, radiation, and wave action. CROSSROADS was not a weapon development operation: the bombs used were of the same design as the one dropped on Nagasaki.

Effects experiments were intended to acquire urgently needed military data. These experiments may be classed into two general kinds. The first class of measurements was made to document the hostile environment created by the nuclear detonation. The second class of effects experiments documented the response of systems to the hostile environment: these measurements are termed systems response experiments.

Environmental Measurements

The purpose of environmental effects measurements was to gain a comprehensive view of the hostile environment created by a nuclear detonation to allow military planners to design survivable military hardware and systems and to train personnel to survive. Examples of environmental measurements taken at CROSSROADS include static (crushing) and dynamic (blast) pressure, heat generated by the detonation, and fallout radiation. Measurement techniques employed for CROSSROADS varied with the effects being measured, but usually measuring devices were placed at a variety of ranges from surface zero and their measurements recorded in some way. Many types of gauges and data-recording techniques were used. Measuring devices or instruments were airborne, underwater, on shore towers, or on a technical support vessel: the majority were placed on target vessels (Reference C.9.208, p. 2).

Rugged, self-recording gauges were developed for blast and thermal radiation measurements so that complete loss of data from a project would not occur if instrument recovery were delayed, for example, by heavy fallout. For nuclear radiation measurements, however, early data recovery was still desirable as the gauges might be thin aluminum foil meters that could be made radioactive by the initial neutrons. Early observation was necessary before the information contained in the induced radiation pattern decayed to undetectable levels.

The potential for radiation exposure of personnel responsible for environmental measurements in general depended on the proximity of the instruments to

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