Resonance Fluorescence inIr191

Abstract

Resonance fluorescence from ${\mathrm{Ir}}^{191}$ has been investigated with ${\mathrm{Pt}}^{191}$ as the source of the exciting radiation. The centrifuge technique was used for the compensation of the recoil energy losses. The known level at 539 keV was excited and a mean lifetime of (${1.1}_{\ensuremath{-}0.3}^{+0.7}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}11}$ sec was determined. A second level excited at (590\ifmmode\pm\else\textpm\fi{}15) keV might be identical with that suggested at 584 keV. The limits for the mean lifetime $\ensuremath{\tau}$ are $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}<\ensuremath{\tau}<1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$ sec. No resonance fluorescence was observed from the 625-keV level. The small transition probabilities for the $\ensuremath{\gamma}$ transitions from the 539- and the 625-keV levels to the ground-state band are not compatible with the previous assignment to Nilsson orbit (402)\ensuremath{\uparrow}. A satisfactory agreement with the Nilsson model was obtained by assuming that these levels belong to the rotational band built on Nilsson state (411)\ensuremath{\uparrow}.