We are involved in a program to study the antimatter components of the
cosmic rays in outer space. We present the performances of a transiti
on radiation detector we have built for positron identification during
a balloon flight 4-50 Gev. We present also the design and expected pe
rformances of a similar detector we intend to build for a future exper
iment (PAMELA), to be run on a satellite by the end of 1999, in order
to complete this program with higher statistics and at higher energies
, namely about 200 GeV.