SCINTILLATION COUNTER

Radiation Detectors SCINTILLATION COUNTER SCINTILLATION COUNTER The scintillation counter is a solid state radiation detector. EO 2.7 DESCRIBE the operation of a scintillation counter to include: a. Radiation detection b. Three classes of phosphors c. Photomultiplier tube operation The scintillation counter is a solid state radiation detector which uses a scintillation crystal (phosphor) to detect radiation and produce light pulses. Figure 24 is important in the explanation of scintillation counter operation. As radiation interacts in the Figure 24 Electronic Energy Band of an Ionic Crystal scintillation crystal, energy is transferred to bound electrons of the crystal’s atoms. If the energy that is transferred is greater than the ionization energy, the electron enters the conduction band and is free from the binding forces of the parent atom. This leaves a vacancy in the valence band and is termed a hole. If the energy transferred is less than the binding energy, the electron remains attached, but exists in an excited energy state. Once again, a hole is created in the valence band. By adding impurities during the growth of the scintillation crystal, the manufacturer is able to produce activator centers with energy levels located within the forbidden energy gap. The activator center can trap a mobile electron, which raises the activator center from its ground state, G, to an excited state, E. When the center de-excites, a photon is emitted. The activator centers in a scintillation crystal are referred to as luminescence centers. The emitted photons are in the visible region of the electromagnetic spectrum. Rev. 0 Page 45 IC-06