Large-area Photocathode Research Articles

Quantum Efficiency of P3HT a new Air-Stable Photocathode for use in Gaseous UV Photon Detectors

We present the QE results of a new air stable organic semiconductor UV photocathode P3HT. QE was measured as a function of wavelength in spectral range 190-250nm. It shows nonnegligible QE near 230nm. Though QE is low as compared to CsI but due to ease of preparation of large area photocathodes and air stability it may replace CsI in some experiments where photon flux is high.

Aging behavior of large area MCP–PMT

The Institute of High Energy Physics, Chinese Academy of Sciences have designed a new type of photomultiplier tube (PMT) based on microchannel plates (MCPs) with large area photocathode, known as large area microchannel plate photomultiplier tube (MCP–PMT). The aging characteristics of the large area MCP–PMTs are different from dynode PMTs and small proximity-focus MCP–PMT. In this work, a prototype large area MCP–PMT was aged by operating with nearly 1000 photoelectrons per pulse for 3 months, and aging process of the MCP–PMT was discussed based on the aging curve.

The X-HPD—A modern implementation of a SMART concept

The concept of hybrid photodetectors which combine a large area photocathode with a crystal scintillator anode in the centre of a hemispherical vacuum tube was demonstrated first with the Philips SMART tubes and, more recently, with the QUASAR tubes of the Lake Baikal experiment. Photoelectrons from the cathode are accelerated by a potential difference of 20–30 kV and deposit their kinetic energy in the scintillator (or Phosphor). The generated scintillation light is detected by a small and low cost photodetector, e.g. a conventional PMT. The X-HPD study is a variation of this concept aiming at improved performance and maximum simplicity. The glass envelope is essentially spherical and a spatial scintillator crystal is mounted in its centre. The spherical symmetry leads to a uniform collection efficiency and very small intrinsic time spread over the full viewing angle of 120° (3 π solid angle). We report about test results of a the first X-HPD prototypes of 208 mm diameter with cylindrical and conical LYSO crystal anodes.

Quantum efficiency measurement system for large area CsI photodetectors

A proximity focusing freon/CsI RICH detector has been built for kaon physics at Thomas Jefferson National Accelerator Facility (TJNAF or Jefferson Lab), Hall A. The Cherenkov photons are detected by a UV photosensitive CsI film which has been obtained by vacuum evaporation. A dedicated evaporation facility for large area photocathodes has been built for this task. A measuring system has been built to allow the evaluation of the absolute quantum efficiency (QE) just after the evaporation. The evaporation facility is described here, as well as the quantum efficiency measurement device. Results of the QE on-line measurements, for the first time on large area photocathodes, are reported.

Laterally resolved measurements of polycrystalline cesium iodide surfaces

The aim of this work was to establish the correlation between the local chemical composition and morphology of polycrystalline cesium iodide (CsI) and its local quantum efficiency. We used a laterally resolved Electron Spectroscopy for Chemical Analysis (ESCA-300) apparatus and a Scanning Auger Microprobe (SAM) to investigate the lateral inhomogeneity of the CsI surface stoichiometry. The local quantum efficiency (QE) was determined by measuring the secondary electron emission in Photoemission Electron Microscopy both with a non-monochromatized deuterium lamp and with tunable X-ray synchrotron radiation as the excitation source. CsI films on different substrates were studied. We found that the local QE depends strongly on the morphology, on the local stoichiometry and on carbon contamination. The results allow for an optimisation of the quantum efficiency of large area photocathodes.

Recent results on the properties of CsI photocathodes

We report here on the results obtained by the CERN RD26 collaboration on the production and characterization of large area photocathodes, susceptible to equip fast UV-photon imaging devices. Such detectors are planned for some Ring Imaging Cherenkov (RICH) detector projects, in particular HADES at SIS Darmstadt, BABAR at the SLAC asymmetric B-factory, and ALICE at the LHC (CERN).

The Decay Times of Organic Scintillators and Their Application to the Discrimination between Particles of Differing Specific Ionization

Studies of the differences in the decay time of organic phosphors have shown that, while most of the light is emitted with a short-period fluorescence decay, differences in specific ionization affect the long-term components. It is consequently possible to distinguish between gamma ray and neutron excitation of many phosphors (including scintillating liquids) by using multiplier photocells having relatively slow response characteristics. Photomultipliers with large-area photocathodes can therefore be used.