Lifetimes of the Levels at 265 and 280 keV inAs75

The centrifuge technique has been applied to observe resonance fluorescence from the levels at 265 and 280 keV in ${\mathrm{As}}^{75}$. Using a Li-drifted germanium detector, it became possible to separate the two resonance lines completely. The resulting mean lifetimes are ${\tau }_{265}=(1.71\mathrm{}\pm 0.10)\times {10}^{-11\mathrm{}}$ sec and ${\tau }_{280}=(4.02\mathrm{}\pm 0.30)\times {10}^{-10\mathrm{}}$ sec. The angular distributions of the resonantly scattered radiations yielded $M1\mathrm{}-E2\mathrm{}$ mixing ratios of ${\delta }_{265}=-(0.01\mathrm{}\pm 0.04)$ and ${\delta }_{280}=-(0.42\mathrm{}\pm 0.08)$, in agreement with previous results.