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Crystals from China

The largest of the LEP experiments, by far, is L3, a collaboration led by Nobel Laureate Sam Ting. L3 brought together institutes from 17 countries spread throughout the World.

L3 aimed to specialize in measuring electrons, positrons, and photons emerging at small angles to LEP's colliding beams with the best possible precision. To achieve this, special crystals made from Bismuth Germanate, BGO, were chosen. Such crystals had previously only been made in small quantities, a few cubic centimetres, and never with the purity required by L3. The experiment would need a massive 12 tons of BGO crystals.

A group of about a hundred physicists and engineers from China, France, Germany, Holland, Hungary, Italy, Switzerland, the USA and the USSR was set up to find a solution. It soon became clear that only the Shanghai Institute of Ceramics (SIC) would be capable of producing such a large number of crystals, some 11 000 in total, with the needed quality, within the timescale, and at an affordable price

An industrially produced BGO crystal for use in medical imaging.

National sensibilities were quickly forgotten as Russia agreed to furnish five tons of Germanium Oxide, a highly strategic material, China supplied the highly pure Bismuth Oxide and French industry developed new machines for crystal cutting and polishing.

Industrial production of BGO crystals started in 1985, and the finished crystals were delivered to CERN in June 1987. More than 95% passed the most critical quality control tests on arrival at the Laboratory. Final assembly, testing, and mounting was enthusiastically performed by all the teams in L3's BGO group, and the detector was fully operational when LEP started up in 1989.

But the BGO story does not end there. The close collaboration between experts from different nationalities has created bonds of confidence and friendship forming a solid basis for future collaboration. Thanks to L3, BGO crystals are now widely used in detectors for medical diagnosis, in particular in the USA, and Chinese industry has the lion's share of the world's crystal production.

Co-operation across the world made L3's BGO detector possible.


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