Summary
Lifetime measurements by the Doppler shift attenuation method for levels in the nuclei57Fe and57Co, populated via the reactions55Mn(α, pnγ)57Fe and55Mn(α, 2nγ)57Co, respectively, are reported. The relative γ-ray intensities and the branching ratios for levels in the two nuclei are also presented. In57Fe, mean lifetime values of τ=(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 τ=0.08±0.03, 0.54 +0.30−0.15 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 in57Fe a lower limit of 2 ps is obtained for its mean life. In57Co lifetimes of eight levels withJ 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.
Riassunto
Si riportano le misure di vita media mediante il metodo di attenuazione dello spostamento Doppler per livelli nei nuclei57Fe e57Co popolati mediante le reazioni55Mn(α, pnγ)57Fe e55Mn(α, 2nγ)57Co, rispettivamente. Si presentano anche le intensità relative dei raggi γ e i rapporti di diramazione nei due nuclei. Per57Fe si ottengono i valori di vita media di τ=(0.20±0.09) ps e (0.26±0.10) ps per i livelli a 1007.0 keV e 1356.8 keV, rispettivamente, per i quali non esistevano precedentemente informazioni sulla vita media, e si determinano i valori di τ=0.08±0.03, 0.54 +0.30−0.15 e (0.16±0.06) ps per i livelli a 2355.7, 3269.1 e 6185.6 keV, rispettivamente, per i quali si erano stati riportati precedentemente solo i limiti di vita media. Per il livello a 2455.2 keV nel57Fe si ottiene per la sua vita media un limite inferiore di 2 ps. Nel57Co le vite medie degli otto livelli conJ π≤19−/2 sono state misurate e confrontate con valori riportati precedentemente. Si discutono i risultati delle misure di vita media e le probabilità di transizione ridotte per entrambi i nuclei e si confrontano con i calcoli disponibili del modello a strati.
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Banerjee, P., Sethi, B., Chatterjee, J.M. et al. Doppler shift attenuation measurements on57Fe and57Co. Nuov Cim A 85, 54–66 (1985). https://doi.org/10.1007/BF02902389
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DOI: https://doi.org/10.1007/BF02902389