Influence of water on optical parameters of aerogel

Influence of water adsorbed in aerogel on its optical parameters has been studied. For the first time it was obtained that a very little amount of adsorbed water results in a degradation of the light absorption length (Labs). The time constant of Labs degradation process has been measured for the first time. It is about 20 days and greater than the time constant of a water adsorption process by two orders of magnitude. Labs degradation can be explained by a contamination of aerogel by metals such as Fe and Co. Data on the influence of water on the refractive index and the light scattering length are presented. The procedure of aerogel selection for use in Cherenkov counters with the diffusive light collection has been suggested.