A firefighter with a thermal imager can see the source of a fire through smoke. But how do you see a radiation source that has no smell, no glow, and no heat? Gamma cameras solve this problem: they capture gamma rays emitted by radioactive materials and overlay their 'trace' onto a regular photograph. The result is an image showing that the source is, say, behind the far door.
In this new study, two types of such cameras were compared: those with semiconductor detectors and those with scintillators. A scintillator is a crystal that flashes with light when struck by a gamma quantum; a semiconductor directly converts radiation into an electrical signal. The first camera proved faster and more sensitive when searching for a 'hot zone' in the field, while the second was more accurate in determining which isotope is present. Therefore, the authors propose using them sequentially: first a scintillator for detection, then a semiconductor for identification.
This staged approach resembles the work of a detective: first a general survey of the scene, then a thorough examination of the evidence. In the future, cameras combining both methods in a single unit may appear, but for now, the proven pair of 'scintillator + semiconductor' covers the main needs of nuclear safety.
Gamma cameras used for locating radioactive sources come from astrophysics and medical physics — the same detectors are used in space telescopes and positron emission tomography scanners.