Scintillation counter

The first electronic scintillation counter was invented in 1944 by Sir Samuel Curran[1][2] whilst he was working on the Manhattan Project at the University of California at Berkeley.

The first commercial liquid scintillation counter was made by Lyle E. Packard and sold to Argonne Cancer Research Hospital at the University of Chicago in 1953.

For gamma rays (uncharged), their energy is converted to an energetic electron via either the photoelectric effect, Compton scattering or pair production.

The chemistry of atomic de-excitation in the scintillator produces a multitude of low-energy photons, typically near the blue end of the visible spectrum.

The scintillator must be shielded from all ambient light so that external photons do not swamp the ionization events caused by incident radiation.

To achieve this a thin opaque foil, such as aluminized mylar, is often used, though it must have a low enough mass to minimize undue attenuation of the incident radiation being measured.

Sodium iodide (NaI) containing a small amount of thallium is used as a scintillator for the detection of gamma waves and zinc sulfide (ZnS) is widely used as a detector of alpha particles.

However, detectors based on semiconductors, notably hyperpure germanium, have better intrinsic energy resolution than scintillators, and are preferred where feasible for gamma-ray spectrometry.

These include scintillation counters designed for freight terminals, border security, ports, weigh bridge applications, scrap metal yards and contamination monitoring of nuclear waste.

There are variants of scintillation counters mounted on pick-up trucks and helicopters for rapid response in case of a security situation due to dirty bombs or radioactive waste.

[6] In the United Kingdom, the Health and Safety Executive, or HSE, has issued a user guidance note on selecting the correct radiation measurement instrument for the application concerned.

Schematic showing incident high energy photon hitting a scintillating crystal, triggering the release of low-energy photons which are then converted into photoelectrons and multiplied in the photomultiplier
Apparatus with a scintillating crystal, photomultiplier , and data acquisition components.
animation of radiation scintillation counter using a photomultiplier tube.
Scintillation probe being used to measure surface radioactive contamination. The probe is held as close to the object as practicable
Hand-held large area alpha scintillation probe under calibration with a plate source in a bench calibration jig.
Hand-held scintillation counter reading ambient gamma dose. The position of the internal detector is shown by the cross
Measurement of gamma ray spectrum with a scintillation counter. A high voltage drives the counter which feeds signals to the Multichannel Analyser (MCA) and computer.