Doppler shift attenuation measurements on 57Fe and 57Co

Lifetime measurements by the Doppler shift attenuation method for levels in the nuclei 57Fe and 57Co, populated via the reactions 55Mn(α, pnγ)57Fe and 55Mn(α, 2nγ)57Co, respectively, are reported. The relative γ-ray intensities and the branching ratios for levels in the two nuclei are also presented. In 57Fe, mean lifetime values of tau = (0.20 +-0.09) ps and (0.26 +- 0.10) ps are obtained for the levels at 1007.0 keV and 1356.8 keV, respectively, for which no lifetime information existed previously and values of tau = 0.08 +- 0.03, 0.54sub(-0.15)sup(+0.30) and (0.16 +- 0.06) ps are determined for the levels at 2355.7, 3269.1 and 6185.6 keV, respectively, for which only the limits of lifetimes were reported earlier. For the 2455.2 keV level in 57Fe a lower limit of 2 ps is obtained for its mean life. In 57Co lifetimes of eight levels with Jsup(π) <= 19-/2 have been measured and compared with the earlier reported values. The results of lifetime measurements and reduced transition probabilities for both the nuclei are discussed and compared with the available shell model calculations