Nuclear Resonance Fluorescence from the 279-kev Level ofTl203with an Ultracentrifuge

Abstract

Resonance fluorescence from the 279-kev level of ${\mathrm{Tl}}^{203}$ was studied with the centrifuge method. Assuming a total conversion coefficient ${\ensuremath{\alpha}}_{T}=0.225$, a mean life ${\ensuremath{\tau}}_{\ensuremath{\gamma}}=(5.00\ifmmode\pm\else\textpm\fi{}0.24)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec for gamma-ray emission was calculated from the resonance scattering measured at different source velocities. Combining this lifetime with the $B(E2)$ from Coulomb excitation, the absolute value of the mixing amplitude $\ensuremath{\delta}={(\frac{E2}{M1})}^{\frac{1}{2}}$ is $|\ensuremath{\delta}|={{1.31}_{\ensuremath{-}0.18}}^{+0.24}$. The angular distribution of the resonance radiation was found to be of the form $W(\ensuremath{\theta})=1+(0.87\ifmmode\pm\else\textpm\fi{}0.08){P}_{2}(cos\ensuremath{\theta})$. This angular distribution, together with the range of absolute values of $\ensuremath{\delta}$ given above, fixes the sign of $\ensuremath{\delta}$ as positive. The range of $\ensuremath{\delta}$ values permitted by the angular distribution measurements is $\ensuremath{\delta}=+{{1.20}_{\ensuremath{-}0.12}}^{+0.20}$.