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

We performed studies in the operation of various hole-type gaseous multiplication structures (GEM, capillary plates, and others) at very high fluxes of X-rays (<60 keV-bremsstrahlung) 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/; in the case of gammas it reached levels of up to 10/sup 9/ Hz/mm/sup 2/ during the pulses. In most measurements, the entire area of the detector 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.