Crystal Calorimeter

  A calorimeter made of homogeneous cells and towers, of high-Z inorganic scintillating materials, e.g. NaI(Tl), BGO, BaF₂, CeF₃, or CsI.

The materials may be impurity-activated scintillators such as NaI(Tl), or pure crystals like BGO; the latter are free from problems associated with non-uniform dopant distribution, but are usually also harder to grow. Materials are characterized by their radiation length X₀ (ranging from 1.1 to 2.5 cm), and interaction length (ranging from 22 to 41 cm), the light yield in photons per MeV and wavelength of emitted light, signal rise and decay times, afterglow (duration of light emission after excitation), etc. Overall, it is the physical size (cost) and the energy resolution that usually count most. Resolutions down to have been discussed ([Ferrere92], [Lecoq93]). For a comparison of crystals, [Gratta94] or [Majewski92], also [Barnett96].