Study of hole-type gas multiplication structures for portal imaging and other high counting rate applications

We performed studies of operation of various hole-type gas multiplication structures (GEM, capillary plates and others) at very high fluxes of X-rays (<60 keV - brehmstrahlung) and pulsed gamma radiation (< 50 MeV bremsstrahlung). In the case of X-rays the counting rate was 10/sup 5/-10/sup 6/ Hz/mm/sup 2/ and in the case of gamma it reached up to 10/sup 9/ Hz/mm/sup 2/ during the pulses. In most of the measurements all detector-area was exposed to these extremely high fluxes. Results obtained so far indicate that the GEM and the hydrogen treated capillary plates could be successfully used in medical imaging applications.