Probability of Production of Internal Bremsstrahlung Accompanying $\beta$ Decay from ${\mathrm{Tl}}^{204}$, ${\mathrm{Pm}}^{147}$, and ${\mathrm{Ca}}^{45}$

The production of internal bremsstrahlung accompanying $\beta$ decay from radioactive nuclei of ${\mathrm{Tl}}^{204}$, ${\mathrm{Pm}}^{147}$, and ${\mathrm{Ca}}^{45}$ has been investigated. The $\beta$-active source is fixed to the source holder of an experimental chamber with a good collimating arrangement. The internal bremsstrahlung is detected by a scintillation counter of good resolution and known efficiency, and a differential spectrum is obtained using a single-channel pulse analyzer. After making all necessary corrections, the probability of internal bremsstrahlung /$m{c}^2$ per $\beta$ disintegration is obtained. The experimental probability is compared with the theoretical probabilities calculated from the theories of Knipp, Uhlenbeck, and Bloch; Nilsson; and Lewis and Ford. Discrepancies have been observed between experimental and theoretical results, especially in the case of ${\mathrm{Ca}}^{45}$, which has not been investigated previously. The experimental results show a distinct deviation from theoretical predictions.