田端 誠

It is need threshold type Cherenkov counters with the reftactive index of about 1.1 to identify protons from kaons and pions in the momentum range of 1-2 GeV/c in a bigger stage. There were no materials having such reftactive indices in ordinary temperature and ordinary pressure But we found the production method of silica aerogel with high reftactive indices. (2005NSS N14-191) By our research and development works of two years, production parameters were modified and transmission length at the wavelength of 400nm achieved more than 20min at index range of L 08 < n < 1 25. We nil/ perform the beam test experiments with the electron beams (LAS, Tohoku Univ.) in May and September, and the proton beams (HIMAC, AIRS) in this autumn. We will report the results in this presentation

TANPOPO, dandelion, is the name of a grass whose seeds with floss are spread by the wind. We propose the analyses of interplanetary migration of microbes, organic compounds and meteoroids on ISS-JEM. Ultra low density aerogel will be used to capture micrometeoroid and debris. Particles captured by aerogel will be used for several analyses after the initial inspection of the gel and tracks. Careful analysis of the tracks in the aerogel will provide the size and velocity dependence of debris flux. The particles will be analyzed for mineralogical, organic and microbiological characteristics. To test the survival of microbes in space environment, microbial cells will be exposed. Organic compounds are also exposed to evaluate the possible denaturation under the conditions. Aerogels are ready for production in Japan. Aerogels and trays are space proven. All the analytical techniques are ready.

A proximity focusing RICH with aerogel radiator has been studied to extend the pion-kaon separation power in the forward region of the Belle spectrometer. Such a proximity focusing RICH counter is also a very fast detector, in particular if a micro-channel plate (MCP) PMT is used as the photon detector. With its excellent timing properties, the same device could also serve as a time-of-flight counter and thus supplement other identification methods, in particular for low momentum tracks. Cherenkov photons emitted in the radiator medium (aerogel) as well as in the entrance window of the PMT could be used for the time-of-flight measurement. A prototype of this novel device using BURLE 85011 64-anode, microchannel plate PMT, was tested on the bench and in the test beam at KEK. Excellent performance of this counter could be demonstrated. In particular, a good separation of pions and protons was observed in the test beam data with a time-of-flight resolution of about 35 ps (rms) for Cherenkov photons produced in the PMT window.

A proximity focusing RICH using aerogel as the Cherenkov radiator is being developed as a new particle identification device for the Belle detector upgrade. A prototype counter was constructed with recently produced aerogel samples, arranged in a focusing configuration, and a test beam experiment was carried out in order to evaluate the performance of the apparatus. With this device we have achieved a pi-K separation that exceeded 5 sigma at 4 GeV/c, with approximate to 9 detected photoelectrons per track. We have also studied the influence of various parameters like radiator refractive index combinations on the performance of the apparatus.

New production methods of silica aerogel with high and low refractive indices have been developed. A very slow shrinkage of alcogel at room temperature has made possible producing aerogel with high refractive indices of up to 1.265 without cracks. Even higher refractive indices than 1.08, the transmission length of the aerogel obtained from this technique has been measured to be about 10 to 20 mm at 400 nm wave length. A mold made of alcogel which endures shrinkage in the supercritical drying process has provided aerogel with the extremely low density of 0.009g/cm(3), which corresponds to the refractive index of 1.002. We have succeeded producing aerogel with a wide range of densities.

Silica aerogel with the refractive index of around 1.2 has been developed. It is argued that a Cherenkov counters with using this silica aerogel could be applied as a new gamma detector of positron emission tomography. Since a Cherenkov photon is emitted in a radiator of n > 1.156 for a 511 keV electron and that of n >(sic)1.25 for 341 keV one (compton edge of 511 keV gamma), only photoelectric effect could be detected. The time resolution of a Cherenkov counter is essentially more superior than that of a scintillation counter. The TOF measurement could determine the three dimensional coordinate of the annihilation position of the positron with sufficient resolution. The production method of silica aerogel with such refractive index is shown. The expected properties of this Cherenkov counter are discussed. A simple proof-of-principle experiment confirms the feasibility of the new PET detector.