  We propose a novel antiparticle detector. The gaseous antiparticle
spectrometer (GAPS) effects particle identification through the characteristic
X-rays emitted by antiparticles when they form exotic atoms in gases. GAPS
obtains particularly high grasp (effective area--solid angle product) at lower
particle energies, where conventional schemes are most limited in their
utility. The concept is simple and lightweight, so it can be readily employed
on balloon and space-based missions. An extremely powerful potential
application of GAPS is a space-based search for the neutralino through the
detection of a neutralino annihilation by-product -- the antideuteron.
Paradoxically, this space-based search for the neutralino is capable of
achieving comparable sensitivity to as yet unrealized third generation,
underground dark matter experiments. And GAPS can obtain this performance in a
very modest satellite experiment. GAPS can also provide superior performance in
searches for primary antiprotons produced via neutralino annihilation, black
hole evaporation and in probing subdominant contributions to the antiproton
flux at low energies. In a deep space mission GAPS will obtain higher
sensitivity for a given weight and power than BGO calorimeters.
