rads) or fractionated (6800, 8500, 11,000, or 13,300 rads) doses of pulsed mixed gamma-neutron radiation. The fractionated doses were delivered as two equal fractions 5 hours apart. The pigs were trained to traverse a shuttlebox when presented with visual and auditory cues and their postirradiation performance was tested at specified intervals until death. iii Miniature pig performance after the second half of the fractionated dose was similar to or better than the performance observed after

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... first half of the dose. The pig's performance was markedly better when the dose was fractionated than when it was unfractionated; early transient incapacitation was shorter, and acceptable performance was achieved earlier and lasted longer. Also, mean survival times for the pigs that received fractionated doses were longer. Permanent performance decrement and incapacitation occurred immediately in several pigs at all dose levels when the dose was unfractionated. When the dose was fractionated, however, only at the highest dose of 13, 300 rads were any pigs similarly affected. The results of this study indicate that fractionated doses of pulsed mixed gamma-neutron radiation affect miniature pigs much less severely than do equivalent unfractionated doses.