The SPA technique is dependent on the energy conversion of radioactive decay, which releases light photons which can be detected via the use of some devices such as the photomultiplier tubes of scintillation counters or CCD imagers.
While this particle travels in the medium, the energy it possesses is dissipated as it collides with the surrounding molecules in the solvent, exciting them while doing so.
For instance, the decay of a Tritium atom releases a beta particle, which is well-suited to SPA due to a very short (1.5 μm) path length through water.
Another device is known as CCD Imager, which is composed of a set of cooled digital cameras with sensitive charge coupled device detectors and with some refined telecentric lenses to convert the captured photon energy into high quality images.
In comparison to the previous over-coated plate-based methods, SPA has a number of advantages that makes it more popular: