Internal bremsstrahlung spectra from ${\mathrm{S}}^{35}$ and ${\mathrm{Pm}}^{147}$ have been investigated with the NaI scintillation spectrometer. Both the absolute cross section of production and the energy distribution agree with theoretical predictions. The theoretical internal bremsstrahlung spectrum of RaE was calculated by using both the observed forbidden $\beta$ spectrum and an allowed $\beta$ distribution. No significant differences in shape were found in these two cases except in the absolute cross section of production.

The ionization accompanying beta decay was studied in the case of RaE and also in ${\mathrm{Pm}}^{147}$ by measuring the characteristic x-rays in an NaI scintillation counter as well as in a proportional counter spectrometer. Both $K$ and $L$ radiations were observed, and their absolute cross sections were compared with the theoretical calculations of Migdal, Feinberg, and Levinger. Because of the approximate nature of the theoretical calculations, the agreement between the theoretical and experimental results is considered satisfactory.

• Received 7 October 1953

DOI:https://doi.org/10.1103/PhysRev.93.518