ABSTRACT
The study of the passage of photons, electrons, protons, a particles, and neutrons through matter is essentially as old as the discovery of these radiations themselves. Indeed, it could hardly be otherwise. Original production of energetic photons (x-rays), late in the nineteenth and early in the twentieth centuries, well before the name ‘‘photon’’ was invented, took place in vacuum chambers, and the radiations had to penetrate the walls of the chamber to propagate to detectors. It is worth making a quick observation about the difference between a charged particle passing through matter and a neutral particle. Over many decades, each of the disciplines that has had occasion to study or make use of the passage of energetic particles through matter has historically developed its own traditional terminology that may be inconsistent with, or at least confusing to, another. The dose in matter and the fluence-to-dose conversion factors make sense only for many particles.
