  We study the performances of gaseous and two-phase (liquid-gas) cryogenic
detectors of ionizing radiation based on gas electron multipliers (GEMs) and
operated in an avalanche mode in pure noble gases. The gas amplification in He,
Ar and Kr is systematically studied at low temperatures, using triple-GEM
multipliers. High gains, exceeding 10^4, were obtained in these gases in the
range of 120-300 K. Stable electron avalanching was demonstrated in a saturated
Kr vapor in the two-phase mode. These results are relevant for understanding
basic mechanisms of electron avalanching at low temperatures and for
applications in cryogenic particle detectors, in particular in dark matter and
solar neutrino detectors.
