§ 88. The greater portion of the β ray emission of a radioactive body is formed by the disintegration electrons. Useful qualitative information can be obtained by investigation of the total emission by methods such as measuring the absorption in aluminium, but while these suffice to show the great difference in penetrating power of the β radiation from different bodies they are not suitable for a detailed analysis.

The chief difficulty in investigating the disintegration electrons lies in distinguishing them from those forming the β ray spectra and any other electrons ejected from the outside electronic structure of the atom by subsidiary processes.

The two lines of research which have yielded the most conclusive evidence have been the determination of the total number of electrons emitted by a known quantity of radioactive material, and further the investigation of the distribution of energy among the emitted electrons. The importance of the first type of experiment lies in the fact that since we know there must be one electron emitted from the nucleus of each disintegrating atom, any excess of electrons above this number must be due to secondary processes such as conversion of the γ rays, collisions and so on. We obtain in this way direct and valuable evidence on the extent to which such processes occur.

The distribution of energy among the disintegration electrons is particularly interesting, since it has brought to light a behaviour quite unlike that of the α ray bodies. Instead of a β ray body emitting electrons all of one speed from the nucleus, they appear to be distributed continuously over a wide range of velocity.