  The operation of single-, double- and triple-THGEM UV-detectors with
reflective CsI photocathodes (CsI-THGEM) in Ne/CH4 and Ne/CF4 mixtures was
investigated in view of their potential applications in RICH. The studies were
carried out with UV, x-rays and {\beta}-electrons and focused on the maximum
achievable gain, discharge probability, cathode excitation effects and
long-term gain stability. Comparative studies under similar conditions were
made in CH4, CF4 and Ne/CF4, with a MWPC coupled to a reflective CsI
photocathode (CsI-MWPC). It was found that at counting rates <= 10 Hz/mm^2 the
maximum achievable gain of CsI-THGEMs is determined by the Raether limit; at
counting rates > 10 Hz/mm^2 it dropped with rate. In all cases investigated the
attainable CsI-THGEM gain was significantly higher than that of the CsI-MWPC,
under similar conditions. Furthermore, the CsI-THGEM UV-detector suffered fewer
cathode-excitation induced effects as compared to CsI-MWPC and had better
stability at high counting rates.
