Scintillation counters are important tools for detecting and measuring radioactivity. They work by exposing radioactive materials to atoms within the detector that temporarily absorb the radiated energy. These excited atoms return to their unexcited state and emit photons that are detected by the scintillation counter.
The atoms in a radioactive substance decay, transforming into atoms of a different element and emitting matter and energy.
In a scintillation counter, the radioactive material is dissolved in a solvent containing atoms of a material known to absorb this radiation, called the scintillant. When the atoms absorb this radiation, they become excited. Electrons in these atoms are bumped into a higher energy state with this influx of energy. The electrons do not, however, remain in the elevated energy state for long and return to their base state within a fraction of a second. When the electrons fall to a lower energy state, the atom loses energy in the form of an emitted photon, which is the massless particle of all electromagnetic energy, including light.
These emitted photons interact with atoms within a structure in the counter called the photomultiplier tube, which emits electrons through a process called the photoelectric effect. The resulting electric pulse indicates that photons have been detected, indicating that radioactivity has excited the scintillant. Measuring the pulse allows scientists to determine the level of radioactivity within the substance being tested.