The Beta-Spectrum of RaD

The electronic radiations from a very thin source of RaD are analyzed by means of a proportional counter, operating as a $2\pi$ spectrometer. The $\beta$-rays of the continuum which coincide with the photoelectrons of highest energy form the tail on the pulse distribution which is analyzed to isolate the $\beta$-particles and to compare their spectrum with Fermi theory. The disintegration energy is found to be 64.5±2.5 kev and the limiting energy of the $\beta$-rays = 18±2.5 kev. The form of the spectrum agrees with the theoretical shape for an allowed transition and $E_0=18\mathrm{}$ kev. The presence of a complex system of soft photoelectron peaks, probably emitted mostly in cascade, is deduced from the remarkable shape of the pulse spectrum at low energies (5 to 25 kev).