2-7 May 2010
Oustau Calendal Conference Center
Europe/Paris timezone

Study of Transparent Silica Aerogel with High Refractive Index

6 May 2010, 10:00
Oustau Calendal Conference Center

Oustau Calendal Conference Center

Cassis, France
Poster Technological aspects of Cherenkov detectors Poster Session 2 (Summary)


Dr Ichiro Adachi (KEK)


Highly transparent silica aerogel has been developed for Cherenkov radiator in a RICH counter to be installed in the Belle-II end-cap apparatus. In conjunction with necessity to use multiple aerogel radiator layers for the RICH focusing scheme pioneered by our group, the optical improvement of silica aerogel with higher refractive index range around $n=$1.055$¥sim$1.070 has been intensively carried out since the previous RICH workshop. Generally optical properties of aerogel tiles become poorer as refractive indices go higher, especially at $n>1.055$. This was one of our concerns as the higher index radiator tile has to be located in the downstream in the focusing multiple aerogel radiator layers, where most of Cherenkov photons pass through and therefore higher transparency was required. New aerogel fabrication method, known as "pin-hole drying(PD)" method, to keep its quality in the region of $n>1.055$ was invented. In this method, special care is taken in the aging period of alcogel tiles after the sol-gel process. Based on this technique, optical transparency for $n>1.055$ sample was remarkably improved. For $n=$1.060, we achieved a transmission length of about 50 mm at a wave-length of 400 nm, which is two times longer compared to the previous tiles. The aerogel tile size is another important parameter for a realistic application. By optimizing various conditions, not only in the synthesis process but in the supercritical drying procedure, we have successfully produced a large sample with dimensions of 180$¥times$260$¥times$20 mm$^3$, where optical properties are of the same level as in the case of the smaller ones. New aerogel samples were used as radiators in a RICH prototype to evaluate performance in a test beam experiment done in November 2009 at KEK. The obtained photoelectron yield with new samples was 2.5 times higher than that with the old ones by the previous method. In this contribution, our R¥&D on aerogel improvements will be given.
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