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

Resonance fluorescence from the 279-kev level of ${\mathrm{Tl}}^{203}$ was studied with the centrifuge method. Assuming a total conversion coefficient ${\alpha }_T=0.225\mathrm{}$, a mean life ${\tau }_{\gamma }=(5.00\mathrm{}\pm 0.24)\times {10}^{-10\mathrm{}}$ sec for gamma-ray emission was calculated from the resonance scattering measured at different source velocities. Combining this lifetime with the $B\left(E2\mathrm{}\right)\mathrm{}$ from Coulomb excitation, the absolute value of the mixing amplitude $\delta ={\left(\frac{E2\mathrm{}}{M1\mathrm{}}\right)}^{\frac{1}{2}}$ is $\left|\delta \right|={{1.31}_{-0.18\mathrm{}}}^{+0.24\mathrm{}}$. The angular distribution of the resonance radiation was found to be of the form $W\left(\theta \right)=1+(0.87\mathrm{}\pm 0.08)P_2\left(cos\theta \right)$. This angular distribution, together with the range of absolute values of $\delta$ given above, fixes the sign of $\delta$ as positive. The range of $\delta$ values permitted by the angular distribution measurements is $\delta =+{{1.20}_{-0.12\mathrm{}}}^{+0.20\mathrm{}}$.