Valve methods of recording single alpha-particles in the presence of powerful ionising radiations

In 1926, Greinacher showed that it was possible to detect single α-particles by linearly amplifying the ionisation current due to an α-ray by means of thermionic valves. Subsequently, he was also able to detect single H-particles by the same method. Other workers have since applied the method to various radio-active problems in which the counting would otherwise have had to be done by means of scintillation screens or Geiger counters, etc. The present writers, working in conjunction with H. M. Cave, also employed the method for determining the mean rate of emission of α-particles from radium C, by counting accurately the number of particles emitted within a defined solid angle. While the problem of encounting α- or H-particles can be a comparatively simple matter under certain conditions, there are many experiments necessarily carried out under conditions which render it utterly impossible to employ the Greinacher method in its original form. These experiments involve the counting of comparatively few particles in the presence of disturbances caused by powerful β- or γ- radiation, or by large groups of α-particles which it is not desired to count.