Lifetime measurements in neutron-rich63,65Co isotopes using the AGATA demonstrator

Abstract

Lifetimes of the low-lying (11/2 − ) states in 63,65 Co have been measured employing the recoil distance doppler shift method (RDDS) with the AGATA γ -ray array and the PRISMA mass spectrometer. These nuclei were populated via a multinucleon transfer reaction by bombarding a 238 U target with a beam of 64 Ni. The experimental B(E2) reduced transition probabilities for 63,65 Co are well reproduced by large-scale shell-model calculations that predict a constant trend of the B(E2) values up to the N = 40 67 Co isotope.

Properties of low-lying states in Co65 from lifetime measurements

“…Likewise, Modamio el al. [32] confirmed through lifetime measurements the πf −1 7/2 ⊗ 66 Ni(2 + 1 ) character of the (9/2 − ) and (11/2 − ) states. The tentative (5/2 − , 7/2 − ) states observed by Pauwels et al [17] at 1441.1 and 1625.5 keV are candidates to belong to this πf −1 7/2 ⊗ A+1 Ni(2 + 1 ) quintuplet.…”

“…1222.9 based on the Co and Fe energy systematics [16,17]. Subsequent studies discarded this interpretation claiming a lack of correlation between the B(E2) strengths of the levels [18,32,37]. As shown above, the B(E2;3/2 − 1 → 7/2 − 1 ) in A Co should instead be compared with the B(E2;2 [38].…”

“…† : The (11/2 − ) 1479.4-keV level is not populated in β decay and was not observed in this experiment. Its lifetime is taken from Ref [32]. and has been included here for comparison with the LNPS calculations.Exp.…”

Measurement of lifetimes in Fe62,64,Co61,63 , and Klintefjord1, Ljungvall2, Görgen3 et al. 2017Phys. Rev. CSelf Cite

“…Here, increasing neutron occupation of orbitals above the N = 40 gap manifests itself through the coexistence of spherical and deformed structures at low excitation energy. Even in 67 Co the yrast states can be reasonably well described as a proton particle (hole) weakly coupled to the 2 + 1 state in the corresponding iron (nickel) isotones [14][15][16][17][18].…”

“…Experimental B(E2) values for the neutron-rich iron isotopes are only known for the 2 + 1 → 0 + 1 transitions [8,25,26], but not for higher-lying transitions. For the cobalt isotopes, lifetimes were reported for the 9/2 − and 11/2 − states in 61 Co [36], the 3/2 − and 9/2 − states in 63 Co [16], the 11/2 − state in 63 Co [18], and the 11/2 − and 13/2 − states in 65 Co [18]. For the manganese isotopes some transition strengths are known from Coulomb excitation of 61 Mn [37], and lifetimes were very recently reported for the 7/2 − , 9/2 − , and 11/2 − states in 63 Mn [38].…”