CsI($Tl$) crystal

The technical specifications for production of CsI($Tl$) crystals are required to meet a number of stringent optical and mechanical requirements such as the average light output, light uniformity, dimensions, and radiation hardness. The Budker Institute of Nuclear Physics (BINP) in Novosibirsk, Russia with the collaboration of Single Crystal Institute and Factory in Kharkov, Ukraine, Crismatec Co. in France, and the Shanghai Institute of Ceramics (SIC) in China have produced CsI($Tl$) crystals to meet the Belle ECL specifications.
Optical properties of each crystal were tested by irradiation with a collimated $^{137}$Cs source at nine points along the crystal and measuring photoelectric peaks for 662 keV $\gamma$ rays. Output signals from a standard bialkali photomultiplier tube (Hamamatsu R1847S) were shaped by an amplifier with a 1 $\mu$s shaping time and digitized by a peak-sensing ADC. The nonuniformity of the light collection is defined by the ratio of the difference between the largest and smallest photo-peak values among the nine measurements to the average photo-peak value. The nonuniformity is required to be less than 9 % for all crystals and less than 7 % for 90 % of total crystals.
Measurements of the crystal dimensions were done with an automated device with eight linear gauges. The system has a 20 $\mu$m precision for unwrapped crystals. The lateral dimensions are required to be +0 and $-$200 $\mu$m from the specified dimensions and the length to be $\pm$1 mm from the specified length.