Internal Bremsstrahlung fromPr143andPm147

A NaI(Tl) scintillation spectrometer was used for the study of the spectral distribution of the internal bremsstrahlung from the beta emitters ${\mathrm{Pr}}^{143}$ ($E_{\beta max}=922\mathrm{}$ kev) and ${\mathrm{Pm}}^{147}$ ($E_{\beta max}=226\mathrm{}$ kev). Both the shape of the corrected experimental spectra and the total yield of internal bremsstrahlung measured per beta decay disagree with the original Knipp-Uhlenbeck theory and with the improved version of this theory, which takes into account the nuclear Coulomb field. For ${\mathrm{Pr}}^{143}$ the measured bremsstrahlung yield exceeds that of the Knipp-Uhlenbeck theory by factors of 1.58 (1.48) and 2.56 (1.50) at 50 and 500 kev, respectively. The numbers in parentheses refer to the Coulomb-corrected theory. The corresponding factors for ${\mathrm{Pm}}^{147}$ are 1.58 (1.37) and 6.1 (2.45) at 25 and 150 kev, respectively.