Solid Scintillation Counters
A basic solid scintillation counter consists of a scintillation detector, a PM
tube, a preamplifier, a linear amplifier, a PHA, and a recording device (Fig.
8.1). The most commonly used scintillation detector in g-ray counting is
NaI(Tl), although BGO and LSO are commonly used in PET, discussed
later. Each of these components is described in detail next.
NaI(Tl) Detector
The NaI(Tl) detectors are made of various sizes for different types of equip-
ment. They vary from 3.8 to 50 cm in diameter and 0.63 to 23 cm in thick-
ness. In thyroid probes and well counters, smaller and thicker crystals are
used, whereas larger and thinner crystals are employed in scintillation
cameras.
Photomultiplier Tube
A PM tube consists of a light-sensitive photocathodeat one end, a series
(usually 10) of metallic electrodes known as dynodesin the middle, and an
anodeat the other end—all enclosed in a vacuum glass tube (see Fig. 8.1).
86 8. Scintillation and Semiconductor Detectors
Fig. 8.1. A basic scintillation counter consisting of a NaI(Tl) detector, a photomul-
tiplier (PM) tube, a preamplifier, a linear amplifier, a pulse-height analyzer, and a
recording device. The high voltage applied to the PM tube is typically 1000 V.