Preparation of silica aerogel for Cherenkov counters

Silica aerogel was produced with an index of refraction of n = 1.024 to equip the TASSO Cherenkov detector with 17001 of this radiator medium. In the production process, which is described in detail, different parameters were varied to determine their influence on the shape and the optical quality of the aerogel samples. With the present equipment, samples with a size of 17 × 17 × 2.3 cm3 were manufactured at a rate of 144 pieces per week. A production efficiency of about 90% was obtained. The index of refraction for all samples around n = 1.024 is distributed with σn = 1.3 × 10−3. They have an optical transmission length of Λ = 2.64 cm at a wavelength λ = 436 nm with σΛ = 0.22 cm. For samples with n = 1.017, Λ is found to be about 30% higher.