Nuclear Track Recording

DAVID MALIN
Anglo-Australian Observatory, RMIT University

Among the first ways of studying extraterrestrial cosmic rays was to fly blocks or sheets of photographic emulsions at high altitudes in balloons or aircraft. The highly penetrating cosmic rays interact with the atomic nuclei of the emulsions producing protons, electrons, and mesons. In the emulsion they leave latent image tracks that can be made visible by development. Tracks from nuclear particles can also be rendered visible in a Wilson cloud chamber or a liquid-hydrogen bubble chamber or spark chamber, often attached to a particle accelerator such as cyclotrons and synchrotrons. These chambers were once commonly used as detectors associated with so-called “atom smashers.”

Energetic ionizing particles such as cosmic rays can also produce radiation damage in a variety of dielectric solids, which are insulating materials (polymers) and minerals (mica and glasses). These tracks can be made visible by using various etchants and can give an indication of the direction or intensity of the radiation.

These methods are now of largely historical interest.