Experimental studies of structural optical and photoemission properties of cesium iodide thin film photocathode for high energy physics applications

Abstract

Photocathode devices in the soft X-ray and ultraviolet (UV) energy range are very im- portant area of research in nuclear and particle physics experiments. These photocath- ode devices are employing for Particle Identification (PID) by the means of Ring Imaging CHerenkov technique (RICH). RICH based gaseous photon detector and multiwire propor- tional chamber detector are widely used in experiments like pioneering high energy nuclear interaction experiment (PHENIX), a large ion collider experiment (ALICE) and high accep- tance di-electron spectrometer (HADES) etc. These high energy physics (HEP) experiments requiring a large area photocathode of few square meter or more, which should be capable of individual photon detection and operated at very high magnetic field. These requirements can be met by combining a photocathode and a gaseous electron multiplier (GEM). Cesium iodide (CsI) photocathode is one of the efficient photo-converter and often used in vacuum and gaseous based photon detectors due to its outstanding photoemission and chemical prop- erties. CsI photocathode has high sensitivity, in UV region and can reach dimensions of up to few m 2. CsI also has various applications in other important fields such as in the detec- tion of scintillation light, medical imaging like positron emission tomography (PET). This results a verity of applications in basic and applied science. In the UV wavelength range, CsI photocathodes are being used due to their high QE and good stability in ambient air for short time exposure. A major problem associated with the use of CsI in HEP experiment is the ageing pro- cesses, which ultimately affect the photoemission properties, thus limiting their life time. The development and optimization of large area photocathodes require an exhaustive study of the structural, optical and photoemission properties of the as-deposited and further aged CsI photocathode.