In gamma ray spectrometry performed with High-purity Germanium detectors (HPGe), the detection of low intensity gamma ray lines is complicated by the presence of Compton scattered gamma rays of higher energy. At energies above a few hundred keV, the main interaction in the relatively low Z High-purity Germanium (HPGe) crystal is via Compton interaction. The Compton scattered gamma rays give rise to a continuous background in the gamma-ray spectrum which consequently raises the detection limit for lines at low energies.
A way to suppress these Compton scattered gamma rays is to surround the HPGe crystal with a scintillation material. When Compton scattered gamma rays escape from the HPGe detector and are absorbed and detected in this so-called Compton Suppression shield, they are in time coincident with the gamma photon detected in the HPGe crystal. When one observes coincident signals in HPGe detector and Compton suppression shield, a veto signal can be set to block the registration of the Compton interaction event. This technique is called Compton suppression spectrometry. The detector with which this is done is called an “Anti-Compton Shield” or “Compton Suppression Shield”
For a good suppression it is essential that a wide range in energy of scattered photons is detected in the suppression shield. These energies depend on :The maximum primary gamma ray energy The radiation transmission of the HPGe housing The absorption efficiency of the suppression detector. The direction of the primary incident gamma ray
For an optimum suppression, the suppression shield should be capable of detecting real low energy gamma rays down to 15 keV.