Miniature pigs, trained to traverse, on cue, a two-chambered shuttlebox, received fractionated and unfractionated doses of pulsed mixed gamma-neutron radiation. Performance was significantly better when 6,800- to 13,000-rad doses were delivered in two equal fractions, 5 hours apart, than when given in a single pulse; the early transitory incapacitation period was shorter and the pigs recovered more rapidly to an acceptable performance level. Performance was also significantly better after an 8800-rad fractionated dose given as two 4400-rad fractions from 1/2 to 51 hours apart than after an 8600-rad unfractionated dose. Furthermore, the pigs generally had less severe clinical symptoms (convulsions and coma) after the second half than after the first half of the fractionated doses. When the first dose was reduced to 3400 or to 1700 rads, however, early transient incapacitation did occur after the subsequent 4800- to 5000-rad dose and was more frequently accompanied by convulsions when the initial dose was only 1700 rads. Mean survival times of pigs receiving the fractionated doses were significantly longer than that of pigs receiving equivalent unfractionated doses.

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