Novosibirsk vs. Matsushita

Comparison of the optical characteristics of Matsushita and Novosibirsk aerogels was performed by using the exponential behavior of Belle type. For this measurement, we used a single phototube for read out. The opposite side was covered with a Goretex sheet. Fig. 36 shows the observed number of photoelectrons as a function of the distance from the PMT.

図 36: Comparison of Novosibirsk (n = 1.0077) and Matsushita (n = 1.017) aerogels.

図 37: Comparison of PMT windows. $N_{pe}$ from Novosibirsk (n = 1.0077) is normalized to 1.017.

As the amount of Cerenkov light is propotional to n - 1, the light yield from Novosibirsk aerogel(n=1.0077) is normalized to that of 1.017 refractive index. The extrapolated value at the distance of 0 cm is almost the same($\sim$32 pe) for each aerogel. This is consistent with the normalization in refractive index. It appears that the attenuation length of 29 cm from Novosivirsk aerogel is larger than from Matsushita aerogel. Clearly, Novosibirsk aerogel has a better optical transparency than Matsushita aerogel. On the other hand, Matsushita aerogel has the advantage to be hydrophobic, by which long-term stability as the Cerenkov radiator is ensured [3]. Moreover it has been found to be radiation hard at least up to 9.8 Mrad of gammma-ray dose [4].