Moisture proof columnar cesium iodide (CsI) layers for gas avalanche microdetector

Cesium iodide columnar layers having diameters of ≈3 μm, and with a wall spacing of ≈1 μm act as secondary electron emitters and can be used for detection of radiation: charged particles, X-rays and gamma rays. With a large enough electric field across the columnar layers, ≈400 μm in thickness, gas avalanche gain is evident when placed in a suitable gas, such as P10 or Ar-ethane mixtures. The cesium iodide columns are damaged by ambient moisture. This damage can be prevented by evaporating protecting layers of hydrocarbons, such as anthracene and stilbene or inorganic materials, such as HgI₂. Columnar layers with 20 nm coatings of HgI₂ yield more than 30,000 electrons on average when traversed by electrons from a ⁹⁰ Sr beta source