Structure ofCo65,67studied through theβdecay of

Abstract

The neutron-rich isotopes 65,67 Fe and 65 Co have been produced at the LISOL facility, Louvain-La-Neuve, in the proton-induced fission of 238 U. Beams of these isotopes have been extracted with high selectivity by means of resonant laser ionization combined with mass separation. Yrast and near-yrast levels of 65 Co have also been populated in the 64 Ni+ 238 U reaction at Argonne National Laboratory. The level structure of 65 Co could be investigated by combining all the information from both the 65 Fe and 65 Co β decay and the deep-inelastic reaction. The 65 Fe, 65 Co, and 67 Fe decay schemes and the 65 Co yrast structure are fully established. The 65,67 Co level structures can be interpreted as resulting from the coexistence of core-coupled states with levels based on a low-energy proton-intruder configuration.

β−decay of65Mn to65Fe

“…in 65 Fe, which is then followed by β decay to 65 Co. This decay has no direct β feeding to the ground state of 65 Co and all of the β intensity is then carried out by three γ rays of the energy of 882.5, 1222.7, and 1996.6 keV [24]. In our measurement these transitions have relative intensities summed to I = 163.6(61).…”

“…The energy and efficiency calibrations of the HPGe detectors were made using the sources of 152 Eu, 24 Na, 88 Rb, and 140 Ba. During the whole measurement the energy shifts remained within the ±0.1 keV limit.…”

“…The time response of a Compton events is different from the FEP of the same energy [29]. The procedure started with the construction of an 'approximate prompt curve" (APC) using the Compton events for transitions following the decay of the 24 Na source, and then using this curve to extract 'residual differences" (RD) between the FEP events and the APC curve using different sources. Our procedure is very similar to the one described in detail in Ref.…”

“…The excitation energy of this β − decaying state was measured at 402(10) keV [22,23]. Precise γ -spectroscopic studies established that the two β-decaying states in 65 Fe populate two sets of mutually independent level schemes in 65 Co [24]. The half-lives of the β-decaying states were measured as T 1/2 = 1.12(15) s for the 402-keV (9/2 + ) isomer and T 1/2 = 0.81(5) s for the (1/2 − ) ground state [24].…”

“…Precise γ -spectroscopic studies established that the two β-decaying states in 65 Fe populate two sets of mutually independent level schemes in 65 Co [24]. The half-lives of the β-decaying states were measured as T 1/2 = 1.12(15) s for the 402-keV (9/2 + ) isomer and T 1/2 = 0.81(5) s for the (1/2 − ) ground state [24]. Studies using multinucleon transfer reactions [2] revealed two transitions in 65 Fe which most likely form a high-spin yrast cascade.…”