  The first measurements of light antinucleus production in Au+Au collisions at
RHIC are reported. The observed production rates for antideuterons and
antihelions are much larger than in lower energy nucleus-nucleus collisions. A
coalescence model analysis of the yields indicates that there is little or no
increase in the antinucleon freeze-out volume compared to collisions at SPS
energy. These analyses also indicate that the antihelion freeze-out volume is
smaller than the antideuteron freeze-out volume.
