New Chemical Approach to Increase the Refractive Index, which is a Key Parameter of Aerogels for Cherenkov Radiators
Vavilov-Cerenkov radiation — glow caused by a charged particle in a transparent medium moving at a speed exceeding the phase velocity of light propagation in this medium. Such a glow allows detecting charged particles. The principle of operation of this detector is based on the detection of radiation that occurs when a charged particle moves in a transparent medium with a velocity υ greater than the speed of light u in this medium. Since u= c/n, where the speed of light is in vacuum, and n is the refractive index of the medium, the condition for the appearance of Cherenkov radiation has the form υ > c/n. Accordingly, for radiators of Cherenkov detectors, the most important characteristic is the index of light refraction. According to the refractive index (1.13-1.007), SiO2 aerogels occupy an intermediate position between liquids (water - 1.33) and gases (freon 114 - 1.00014, CO2 10 atm - 1.0043) . This property of aerogels gives a number of advantages in use in Cherenkov detectors in front of liquids and gases, there is no need for high pressures, and the blocks are compact, convenient and easy to use. To increase the number of registered Cherenkov photons, as well as expand the range of particle identification in the direction of small pulses, it is necessary to obtain aerogel blocks with a refractive index higher than 1.07 without deteriorating the optical properties (scattering length, light absorption length and uniformity of the refractive index in the layer).
Here we present a description of various approaches for increasing the refractive index using thermal sintering of blocks , the pinhole method (microholes) , including the original chemical approach developed by us based on the sol-gel method. The so-called chemical approach is based on the introduction of additives in SiO2 aerogel increasing the refractive index. For example, it is zirconium dioxide (ZrO2), the refractive index of which is 2.23; for comparison, the SiO2 has a refractive index of 1.45. The introduction of several mole percent can increase the refractive index by several hundredths of a unit.
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The reported study was funded by RFBR and Novosibirsk region according to the research project № 19-43-543017