Lifetimes of the First and the Third Excited States ofCa41

The lifetimes of the ${\frac{3}{2}}^{-}$ first excited state of ${\mathrm{Ca}}^{41}$ at $E_x=1.95\mathrm{}$ MeV and the ${\frac{3}{2}}^{-}$ third excited state at $E_x=2.47\mathrm{}$ MeV have been measured by the attenuated-Doppler-shift method. The two states were populated through the ${\mathrm{K}}^{41}\mathrm{}(p,n)\mathrm{}{\mathrm{Ca}}^{41}$ reaction at bombarding energies only a little above threshold. The $\gamma$ rays were detected with a lithium-drifted germanium detector. Measurements were made at 0° and 90° to the beam and with ${\mathrm{Ca}}^{41}$ ions recoiling into vacuum, carbon, KCl, and gold. Some attenuation of the Doppler shift results from the recoiling ion changing its direction on collision with a nucleus. At the low recoil velocities encountered, this effect is comparable with the attenuation due to the energy loss in electronic collisions and it was explicitly taken into account. The lifetime of the first excited state was found to be ($4.7_{-1.0\mathrm{}}^{}{}_{}{}^{+2.5\mathrm{}}$) × ${10}^{-13\mathrm{}}$ sec; that of the third excited state is ≥7×${10}^{-13\mathrm{}}$ sec. The speed of the $E2\mathrm{}$ transition to ground from the first excited state is thus about three times the Moszkowski single-particle estimate. In contrast, the speed of the $E2\mathrm{}$ ground-state transition from the third excited state (which decays mainly to the first excited state) is less than 6×${10}^{-3\mathrm{}}$ of the single-particle estimate. These results are compared with theoretical predictions.