Attempt to correlate the ionic model with observations in BaBar RPC chambers and R&D tests

Abstract

The paper presents a model of ionic conduction in the Bakelite-based RPC detectors. This model explains why these detectors need to add water while they operate. To produce the Bakelite polymer, one needs a chemical reaction of the formaldehyde and the phenol molecules. Water is an important byproduct of this chemical reaction. The electrode current, according to the presented model, is formed mainly by the ionic sequence involving the phenol impurities left in the Bakelite and water, both left from the initial production. As long as these two ingredients are present in the original amount, the Bakelite resistance is constant. If either water or phenol impurity are depleted from various reasons, for example due to a large current or presence of a dry gas, the Bakelite resistance increases. According to the presented model, water should be added right from the beginning and not half way through the experiment. Similar ionic process is present in the Linseed oil polymer, where the current is carried by the fatty acid molecular impurities and water. The Bakelite RPC operation requires the entire ionic sequence to operate smoothly to keep the electrode resistance constant.