Both of these features are due to escape eventsi
. The Cd and Te K edges are 26.7 and 31.8 keV
respectively. Photons with incident energy just above these edges undergo photoelectric interactions,
leaving the Cd and Te atoms in an excited state. When the atoms transition to the ground level they often
emit a characteristic X-ray at one of the energies shown in Table 1. Depending on the direction, this X-ray
may leave the CdTe volume so only a small amount of the incident energy is deposited. Such events lead to
fewer full energy events (causing the absorption edges) and more low energy events (below the filter value)
than would otherwise occur. This process is responsible for the escape peaks which are well known in
spectroscopy, but with a tube there is a continuum of escape events. Escape events are more important in
CdTe than in Si or Ge due to the much higher energies of the characteristic X-rays. Fortunately, algorithms
exist to “clean up” this artifact and are available in software sold by Amptek, Inc.