The radiative widths of the $E1\mathrm{}$ transition through the ground isobaric analog states of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Tl}$ and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Pb}$ in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$, respectively, were determined from the cross section of the ($e,e^{\prime }p$) reaction. The results are 98 and 140 eV, respectively, after the correction for the interference from the continuous part of the reaction. They correspond to an effective charge of 0.56 and 21, respectively. The $E1\mathrm{}$ matrix elements were determined and used for the estimation of $\beta$ matrix elements $|i\xi ``\int \overrightarrow{\mathrm{r}}\text{'}\text{'}|$. The result is 0.055 in natural units ($\hslash =c=m_e=1\mathrm{}$) for the $\beta$-decay ${}_{}{}^{207}{}_{}{}^{}\mathrm{Tl}\left(3\mathrm{}{s_{\frac{1}{2}}}^{-1\mathrm{}}\right)\to {}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}\left(3\mathrm{}{p_{\frac{1}{2}}}^{-1\mathrm{}}\right)$. In the case of ${}_{}{}^{209}{}_{}{}^{}\mathrm{Pb}\left(2\mathrm{}{g}_{\frac{9}{2}}\right)\to {}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}\left(1\mathrm{}{h}_{\frac{9}{2}}\right)$, the result is 0.043, which is much larger than the theoretical estimate. For the $E1\mathrm{}$ isobaric analog states of the first excited state of ${}_{}{}^{209}{}_{}{}^{}\mathrm{Pb}$ in ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$, the radiative width and the effective charge were also determined to be 170 eV and 0.46, respectively.

• Received 1 June 1970

DOI:https://doi.org/10.1103/PhysRevC.3.1999