Investigation of the secondary electron emission characteristics of alternative dynode materials for imaging photomultipliers

The requirement to accurately detect and image very high speed photon events is a necessity for many applications across a range of disciplines. Photon imaging detectors often make use of the planar geometry of MCPs for high resolution imaging. However, the inherent rate limitations of MCPs provide opportunities for discrete dynode devices where rapid recharge times and high throughput are required. Novel dynode materials and designs offer the possibility to further improve event time resolution and pulse height distribution. Significant performance advantages can be achieved by increasing the gain of each dynode stage by utilizing materials such as CVD diamond. Secondary electron emission (SEE) coefficients for polycrystalline CVD diamond of 84 have been reported for Hydrogen terminated surfaces and similar values for Cs terminated surfaces [1, 2]. These values are far in excess of currently used materials such as AgMgO(Cs) and CuBeO(Cs) which have SEE coefficients < 15 [3]. Polycrystalline diamond is a widely available, relatively inexpensive material that can be deposited over large areas, making the manufacture of large format imaging detectors a practical possibility. The application of new dynode designs for imaging photomultipliers requires knowledge of the secondary electron emission characteristics of the material. We describe a facility to measure the relevant characteristics of novel dynode materials and designs with 2D imaging capability, and discuss the challenges and complexities involved with SEE coefficient measurements. We present secondary electron emission measurements for a variety of dynode materials and designs and discuss their application in imaging photon-counting devices.