Speaker
Description
The development of Resistive Plate Chambers (RPCs) with improved features like high rate capabilities, higher efficiency in smaller form factors or bigger induced signals requires resistive electrode materials with a specific set of properties. Designing materials for this purpose with specified values of electrical conductivity, that are not usually found in single phase materials, in addition with very good mechanical, chemical, thermal and electrical stabilities has represented a considerable defy in the ambit of materials science, especially when economical aspects are taken into account. Unfortunately, only few materials for electrodes satisfying all these conditions have been found. Even though, the situation worsens when the materials were stressed in the gas discharge environment. We have found that materials that fulfill all of the previously established specifications, even with similar secondary emission, skip the Towsend discharge regime at lower gain than the usual electrode materials. This fact suggests that new requirements for RPC electrode materials should be considered. According to our results, we have found that the chemical nature of the anode seems to have a strong influence on the stability of the avalanche gas conduction regime. This unexpected result was addressed by depositing very thin oxide layers with nm accuracy over polished surfaces of the new materials. Although these films do not significantly modify the electric field distribution inside the RPC, we have found that some thin films stabilize the avalanche regime. Furthermore, being so thin the deposited layer it do not need to be made of a material with a the same hard requirements of high rate resistive electrodes. In this work, we present a simple but very effective solution to make compatible the desirable features of the bulk material working as high rate resistive electrode and the stability of the detector: covering the material with a thin layer of a second phase that stabilize the avalanche discharge regime. Finally, a phenomenological model to explain the experimental method will be exposed for debate.
