The number of particles in beta-ray spectra.—II. Thorium B and thorium (C + D)

Measurements of the number of particles emitted with different velocities in the beta-ray spectra of Radium B and Radium C have been recently described by the writer. In the present paper the measurements have been extended to the spectra of Thorium B and Thorium (C + D). As before, portions of the magnetic spectrum were focussed into a Faraday cylinder, and the number of electrons determined in absolute magnitude. The conclusion reached in the previous paper was that in the case of both Radium B and Radium C there is, underlying the beta-ray lines, a continuous spectrum similar to that of Radium E, and of the same magnitude—that is, containing one electron per atom breaking up. This leaves little doubt that in these three bodies it is the nuclear electrons ejected in the disintegration with varying velocities which form the continuous spectra. If this is true of other bodies we expect to find in the Thorium series also large continuous spectra containing one electron from every disintegrating atom. Ike measurements of the spectrum of Thorium (B + C+ D) by Pohlmeyer showed, however, that the continuous spectrum was feeble in comparison with the beta-ray line Hρ 1398. But since an ionisation method was used, no determination of the absolute number of particles was possible.