Aging of Dielectric - coated Aluminum in Deionized water

Introduction According to present theory, the nuclear processes in the sun give off vast quantities of neutrinos-Experiments confirm the production of these particles, but fail to detect the quantity predicted by theory. The most recent experiments have found a maximum of two thirds the expected number of neutrinos. The Sudbury Neutrino Observatory is being constructed to accurately determine the neutrino flux from the sun. The detector consists of 1000 tonnes of heavy water. Neutrinos entering the heavy water occasionally react in such a way as to produce Cerenkov radiation. This radiation is then detected !by photomultiplier tubes surrounding the heavy water. To increase the detector efficiency, each photomultiplier tube is surrounded by a light reflecting concen-trator composed of dielectric-coated aluminum "petals". Their design is shown in figure nine. These petals must be able to withstand the aqueous environment of the observatory for the 10 year life of the facility. In previous tests, the dielectric-coated petals of aluminum have exhibited degradation after simulated long exposure to deionized water. Measurements of the reflectance of these degraded petals showed an interference pattern caused by the oxidation of the reflective aluminum layer, leaving a 2/im transparent dielectric layer on the aluminum substrate-A series of new tests have been performed to determine what, properties of the deionized water are causing the degradation, and whether the degadafcion is'likely to occur in SNO itself.