ABSTRACT
Vacuum gauges with radioactive emitters that use alpha particles for ionization of residual vacuum atmosphere are called alphatrons. In these gauges, ionization is induced by radiation energy, which is released at the decay of a radioactive substance. The induced charge carriers drift to corresponding electrodes under a weak electric field. Ionization in gases and gas mixtures by alpha particles emitted from radioactive substances such as polonium was studied in the 1950s and earlier. Suitable radioactive materials for gauges with radioactive emitters are those that have a long half-life of their radioactive decay. Radium has 13 isotopes with mass numbers from 213 to 226. Radium is a stable emitter of alpha particles because of its long half-life, but it also is the source of gamma radiation. Plutonium, polonium, and americium have also been used as radioactive sources in gauges with radioactive emitters.
