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w/o Photomultiplier Tubes

C-styles and CP-styles

F EATURES

SCIONIX C-style detector assemblies basically consist of a scintillation crystal which is machined and mounted in a housing of aluminum, stainless steel or copper. In case of hygroscopic crystals the assembly is sealed by a glass or quartz window for optical coupling to a photomultiplier tube or other light detection device. C-style assemblies can be manufactured from low background materials (LB steel or copper).

The standard housing thickness is 0.8 mm. C-style assemblies can be provided in a ruggedized version (CR-styles) or designed for use at elevated temperatures.

The optical window can be extended in height or tapered to form an optical light guide to a different diameter than that of the crystal. For optimum energy resolution, the diameter of the crystal is chosen equal or slightly smaller than the diameter of the PMT.

C-style assemblies are intended for use in combination with customer's photomultiplier tube in demountable assemblies. The optical contact to the PMT is accomplished by using optical coupling compound or customer's own optical glue.

Housings can be equipped with flanges or grooves for O-rings in order to facilitate a demountable coupling to the PMT and its housing.

C-style assemblies can be provided with an axial well and are then called CP-styles, or with thin (30 mm thick) Al entrance windows at the flat side of the crystal, then called CA-styles.

Standard inner well dimensions for CP-style assemblies are

51 CP 51 :  25.4 mm diameter, 39.3 mm deep

                  16.6 mm diameter, 39.3 mm deep

76 CP 76 :  25.4 mm diameter, 52 mm deep

The standard well thickness is 0.3 mm (Aluminium).

 

APPLICATION

Standard C-style assemblies are used for detection of gamma-rays and X-rays between 30 keV and 2 MeV. For higher energies, BGO can be chosen as the scintillator of choice in which case the optical window is omitted. CP-styles are used in well counters for e.g. medical applications or wipe test detectors.
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Thin window crystal assemblies: CA-styles, CD-styles

For the detection of low energy X-ray radiation, a detector can be made intrinsically insensitive to higher energy radiation by choosing the scintillation crystal only a few mm thick. For optimum energy resolution, also at very low (several keV) energies, NaI(Tl) scintillation crystals are often used.

For transmission of the radiation of interest, 30 mm thin Aluminum (Al) windows or 0.2 - 0.3 mm thick Beryllium (Be) windows are used. Al windows are suitable for energies down to 10 keV whereas Be windows can be used down to 3 keV (see Fig. 5.3). The advantage of Al windows is their low cost but Be windows are less easily damaged. For non-hygroscopic crystals, aluminized mylar entrance windows can also be used.

For fast X-ray spectroscopy, thin (0.5 - 1 mm thick) YAP:Ce CA- or CD-styles can be used. Thanks to the decay time of YAP:Ce of only 27 ns (see Table 3.1), count rates of several MHz can be achieved
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