Advances in gas avalanche photomultipliers A. Breskin*, T. Boutboul, A. Buzulutskov, R. Chechik, G. Garty, E. Shefer, B.K. Singh Department of Particle Physics, The Weizmann Institute of Science, 76100 Rehovot, Israel Abstract Gas avalanche detectors, combining solid photocathodes with fast electron multipliers, provide an attractive solution for photon localization over very large sensitive areas and under high illumination #ux. They o!er single-photon sensitivity and the possibility of operation under very intense magnetic "elds. We discuss the principal factors governing the operation of gas avalanche photomultipliers. We summarize the recent progress made in alkali-halide and CVD- diamond UV-photocathodes, capable of operation under gas multiplication, and novel thin-"lm protected alkali- antimonide photocathodes, providing, for the "rst time, the possibility of operating gas photomultipliers in the visible range. Electron multipliers, adequate for these photon detectors, are proposed and some applications are brie#y discussed. 1. Introduction In recent years there have been considerable ad- vances in photon detectors, motivated by the ever- growing complexity of their potential applications. High-resolution localization of light, over a broad spectrum ranging from far UV to the IR, often down to a single-photon level, is requested in vari- ous basic and applied "elds. Numerous examples can be found in particle and nuclear physics, astro- physics, medical imaging, etc. Present photon detection techniques range from tiny cryogenic detectors, employed in astro- * Corresponding author. Tel.: 972-8-9342645; fax: 972-8- 9342611. E-mail address: fnbresk@wisemail.weizmann.ac.il (A. Breskin)  Talk by A. Breskin, dedicated to the memory of the late Pierre Besson. physics, through a variety of small-area solid-state detectors, to vacuum-based devices } reaching dimensions of up to half a meter in diameter. The latter are photomultipliers developed for large under-water astro-particle experiments and are not position-sensitive. Commercially manufac- tured position-sensitive vacuum photomultipliers are limited in size to a few inches in diameter, su!er from a degraded response in moderate magnetic "elds and are rather expensive. Intensive research and development work is taking place in the more recently introduced hybrid photo detectors (HPD) [1]. These vacuum-operated devi- ces could be, in principle, more immune to mag- netic "elds; 5 in. in diameter HPDs, with highly pixelized readout, are developed for particle identi- "cation by the Ring Imaging Cherenkov (RICH) technique, in the "eld of particle- and astro-particle physics [2]. -1- Printed in: Nucl. Instr. & Meth. A442 (2000) pp. 58-67