USE OF WAVE LENGTH SHIFTING FIBRES IN MULTI-SENSOR HIGH ENERGY PHYSICS DETECTORS

摘要

A requirement to collect light from large area scintillators lead to wave length shifting (WLS) technique based on the following principle. Light produced by ionising particle in a scintillator plate after some internal reflections exits the scintillator and hits a WLS bar. Inside the bar the blue light of the scintillator is re-emitted isotropically into longer wave length. Part of the light which lies within angles of internal reflection is trapped. For a polystyrene bar the trapping efficiency is 20-30% (in both directions). The main advantage of the approach is the possibility to squeeze light into a small cross-section (ratio is about 200). The disadvantage is the reduction of light collection about 20 times. The final result is the gain an order of magnitude in comparison with traditional waveguides. Next step ― use of optical fibres that drastically eased construction, long term stability and maintenance. For optical fibres (double cladding) the trapping efficiency is 11%. The smaller trapping efficiency is more than compensated by the large attenuation length (>7 m). Besides fibres are robust and easy to handle. The first use of the technique is related with rectangular bars surrounding large scintillation counters.