Electronic Anticoincidence - Compton Suppression

In gamma-ray spectroscopy, Compton suppression is a technique that improves the signal by preventing data which has been corrupted by the incident gamma ray Compton scattering out of the target before depositing all of its energy. The effect is to minimize the Compton edge feature in the data.

The high resolution solid state germanium detectors used in gamma ray spectroscopy are very small, typically only a few centimeters in diameter and with thickness ranging from a few centimeters to a few millimeters. Since the detectors are so small, it is likely that the gamma ray will Compton scatter out of the detector before it deposits all of its energy. In this case, the energy reading by the data acquisition system will come up short: the detector records an energy which is only a fraction of the energy of the incident gamma ray.

In order to counteract this, the expensive and small high resolution detector is surrounded by larger and cheaper low resolution detectors, usually sodium iodide scintillators. The main detector and the suppression detector are run in anti-coincidence, which means that if they both detect a gamma ray then the gamma ray has scattered out of the main detector before depositing all of its energy and the data is ignored. The much larger suppression detector has much more stopping power than the main detector, and it is highly unlikely that the gamma ray will scatter out of both devices.