Experimental study of theNi66(d,p) Ni67

Abstract

The quasi-SU(3) sequence of the positive parity νg 9/2 ,d 5/2 ,s 1/2 orbitals above the N = 40 shell gap are assumed to induce strong quadrupole collectivity in the neutron-rich Fe (Z = 26) and Cr (Z = 24) isotopes below the nickel region. In this paper the position and strength of these single-particle orbitals are characterized in the neighborhood of 68 Ni (Z = 28, N = 40) through the 66 Ni(d,p) 67 Ni one-neutron transfer reaction at 2.95 MeV/nucleon in inverse kinematics, performed at the REX-ISOLDE facility in CERN. A combination of the Miniball γ -array and T-REX particle-detection setup was used and a delayed coincidence technique was employed to investigate the 13.3-μs isomer at 1007 keV in 67 Ni. Excited states up to an excitation energy of 5.8 MeV have been populated. Feeding of the νg 9/2 (1007 keV) and νd 5/2 (2207 keV and 3277 keV) positive-parity neutron states and negative parity (νpf ) states have been observed at low excitation energy. The extracted relative spectroscopic factors, based on a distorted-wave Born approximation analysis, show that the νd 5/2 single-particle strength is mostly split over these two excited states. The results are also compared to the distribution of the proton single-particle strength in the 90 Zr region (Z = 40,N = 50).

Neutron single-particle strengths at N=40 , 42: Neutron knockout from Ni68,70 ground and isomeric states

“…This transition is not feeding the isomer and no additional prompt transitions were found in coincidence. This, together with the parallel momentum distribution indicating = 1 orbital angular momentum, suggests that this transition depopulates the low-lying 3/2 − state identified at 1724.3(3) keV by Diriken et al at the CERN On-Line Isotope Mass Separator (ISOLDE) facility [42].…”

Nucleon transfer reactions with radioactive beams

“…It is therefore of great interest to locate both the proton and neutron single-particle strength in the region around 68 Ni. A first experiment has been performed at REX-ISOLDE at CERN to study the d( 66 Ni, p) 67 Ni reaction [116,152]. With such heavy beams, and in particular the very low beam energy used in this experiment, causing a low resolution for the excitation energy, the detection of coincident γ-rays is a requirement (see figure 15).…”

Fast-timing spectroscopy at ISOLDE

“…In addition 68 Ni provides a very rich case for shape coexistence, because several 0 + states have been observed below 3 MeV and they seem to originate from excitations across the Z=28 and the N=40 gaps [42]. The neighbouring odd-A nuclei show a significant polarisation of the 68 Ni core when nucleons are coupled, which implies also a reduction of the N=40 subshell [43].…”