Unit 4 Nuclear Threat 4-13 Fallout particles accumulate on the ground, roofs of buildings, bushes, ledges, and all other surfaces exposed to the environment. As fallout accumulates, the unsheltered exposure rate will increase until most of the particles have fallen. At this point, exposure rates will begin to decrease with time due to radioactive decay . The decrease is rapid at first, then gets slower and slower. The exposure rates decrease according to the rate of radioactive decay. Radiological Survey Instruments The most effective method for determining exposure rates is with the use of radiological survey instruments . These survey instruments typically consist of a chamber in which nuclear radiation interacts, yielding an electric pulse or current, and electronic circuitry which converts the current into a meaningful readout. Most survey instruments maintained for emergency management are powered by standard D cell batteries making them portable and fairly easy to maintain in operational condition. Radiological Survey Instrument
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