Track‐recording solids

Since the beginning of the solar system, natural particle detectors have been recording the passage of charged particles from the sun and cosmic rays. Now, in addition to developing the latent images of these fossil trails of damage in solids and learning about the nature of ancient radiation, we are creating new and more sensitive detectors of a similar kind. These detectors, which are finding a wide variety of applications, take advantage of the fact that a highly charged particle penetrating any nonconducting solid leaves a submicroscopic trail that can be chemically amplified. The increased chemical reactivity of the trails of radiationdamaged material is the basis for the so‐called etched‐track process, by which we make the particle tracks large enough to measure in an optical microscope. As we will see, there is sufficient information in the tracks to allow us to determine a particle's charge and velocity.