Columnar cesium iodide (CsI) and micro-hole arrays for use in gas avalanche detectors

The characteristics of a columnar CsI layer with gas multiplication was investigated by using beta rays from a /sup 90/Sr source. This layer is intended for use as the primary electron source in any gas avalanche microdetector to avoid severe performance loss by the oblique angle of the incident charged particle. It was initially thought that the columnar structure might provide a larger detection efficiency than a planar CsI layer, because of the many surface crossings of incident particle for the columnar geometry. The columnar CsI study was performed in a thin parallel-plane structure, which has a 50-500 /spl mu/m gas gap between a columnar CsI cathode and metal anode. We discuss the secondary emission and electric fields in the columnar structure, and explain why, based upon field simulation and experimental results, this approach does not succeed in this case. New ideas are presented for driftless gas avalanche detectors insensitive to the angle of incidence.