Community Research and Development Information Service - CORDIS

Production of radiation hard CSI scintillators for particle physics experiments

Methods for producing radiation hard CsI crystals have been developed. The ratio of the fast scintillation light component to the total light output (the so-called « fast-to-total » value) has been improved from 65% to 80%. The dimensional accuracy has been improved from 0.5 mm to better than 0.1 mm. This improvement has been achieved by an extreme purification of the cesium iodide raw material and by a careful control of the crystal growing process, together with an improved cutting and polishing process.

A cosmic ray tomography apparatus has been built and successfully used to map the three-dimensional response of CsI crystals. Using this method, a major limitation for the energy resolution of the CsI crystals has been identified as the spatial non-uniformity of the light production and collection. To compensate for this effect, a special lacquer has been developed. This lacquer absorbs the UV light produced by the CsI crystal and re-emits it isotropically at a longer wavelength. Using this lacquer, the enrgy resolution for 70 MeV positrons has been improved from 7.5% (FWHM) to 6.0%.

The physical properties of the CsI crystals have been measured in particle beams at PSI and confirmed their high quality. In these tests, two cylindrical wire chambers have been used which were developed especially for the CsI calorimeter.

Using the developed technologies, all CsI crystals needed for the Pion-Beta Detector have been produced and accepted. The Pion-Beta Experiment will start in summer 1998.

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