Types Of Detectors Used in Gamma And X-Ray Detection

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November 29, 2021
scintillation crystal array

The x-ray or gamma energy range of interest, and the application’s resolution and efficiency requirements, all influence the detector type chosen from an application. A scintillation crystal array can be your choice for the best detector. The factors to consider are:

  • Count rate performance
  • Detector compatibility for timing experiments
  • Price

Detectors used in these are:

  • Gas-filled detectors
  • Scintillation detectors
  • Semiconductor detectors

Gas-filled detectors:

 scintillation crystal array

It is a metal chamber containing a positively biased anode wire, filled with gas. Free electrons and positive ions are produced when a photon passes via a gas. An electric pulse is produced when electrons are drawn to the anode.

The electrons may recombine with the ions at low anode voltages. When there is a large density of ions, recombination may occur. An ionization chamber is a detector that collects nearly all electrons at a high voltage. Higher voltages speed electrons toward the anode at energies high enough to ionize additional atoms. This results in a greater quantity of electrons.

A proportional counter is a name for this type of detector. The electron multiplication is considerably stronger at higher voltages, and the amount of electrons gathered is unaffected by the initial ionization. This detector is a Geiger-Mueller counter, in which all photons have the same big output pulse. Continuous discharge happens at much higher voltages.

Scintillation Detectors:

A photomultiplier tube converts a light pulse produced by a gamma-ray interacting with a scintillator into an electric pulse. It comprises a photocathode, a focusing electrode, and 10 or more dynodes, each of which multiplies the number of electrons striking it several times. A chain of resistors is used to bias the anode and dynodes in a plug on tube base assembly.

Qualities of scintillation materials that are necessary for the best detectors include:

  • Transparency
  • Vast size availability
  • Large light output proportional to gamma-ray energy.

Only a few materials have good detection characteristics. Thallium activated Nal and Csl crystals, and a variety of polymers are used. LaBr3 (Ce) crystals are a newer form of scintillation detector material that has better resolution than Nal crystals but has similar properties. With its outstanding gamma-ray resolution and low cost, Nal is still the most common material for gamma detection. Plastics have a far faster pulse light decay and are used in timing applications, despite having little or no energy resolution.

Semiconductor Detectors:

A semiconductor detector is a material that can function as both an insulator and a conductor. Although the terms “solid-state” and “semiconductor” are used interchangeably in electronics. The phrase “solid-state” can apply to solid scintillators in the detector industry.

A semiconductor is a chosen word for detectors made from either elemental or compound single crystal materials with a band gap between 1 to 5 eV. Although other compound semiconductor materials are finding usage in niche applications as development work on them continues. The group IV elements silicon and germanium are by far the most extensively utilized semiconductors.

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