The Alpha Magnetic Spectrometer (AMS) was flown on the space shuttle Discov
ery during flight STS-91 in a 51.7 degrees orbit at altitudes between 320 a
nd 390 km. A total of 2.86 X 10(6) helium nuclei were observed in the rigid
ity range 1 to 140 GV. No antihelium nuclei were detected at any rigidity.
An upper limit on the flux ratio of antihelium to helium of < 1.1 X 10(-6)
is obtained. (C) 1999 Published by Elsevier Science B.V. All rights reserve