Crystal conditioning for high-energy physics detectors

In homogeneous high-resolution calorimetry for particle physics, scintillating crystals can now be considered as a mature technique. In the past decades, several large high-energy experiments have included crystal calorimeters from which a considerable harvest of physics results could be made. To extract the ultimate precision from such calorimeters, great care must be taken in the crystal conditioning, i.e. machining and wrapping or coating. These operations have a strong influence on some key crystal properties for the calorimeter energy resolution, such as light yield and light collection uniformity. In this note, some aspects of machining and of the techniques for uniformizing light collection will be discussed in the light of a recent experiment: L3 at LEP collider, using bismuth germanate crystals and an experiment in construction: CMS for LHC collider, using lead tungstate. To illustrate these techniques, results obtained on medium-scale crystal productions will be shown.