Single-Particle States in Neutron-Rich 69;71Cu by Means of the (d,3He) Transfer Reaction

Pierre Morfouace, Institut de Physique Nucléaire d’Orsay
Monday, Jan 12, 10:00 AM - Special Seminar
1200 FRIB Laboratory

Abstract:  In two (d,3He) transfer reactions with MUST2 at GANIL and the split-pole at Orsay, we have determined the position of the proton-hole states in the neutron-rich 71Cu (N = 42) and 69Cu (N = 40) isotopes. We have found that in 71Cu the hole strength of the πf7/2 orbital lies at higher excitation energies than expected. From β-decay and laser spectroscopy, the πf5/2 first excited particle state in these isotopes was known to come down rapidly in energy when passing N = 40 and even become the ground state in 75Cu. This sudden energy shift has been explained in a number of theoretical works. The prediction for the f7/2 spin-orbit partner was that it would change in energy too through a related effect. Experimentally, the πf-17/2 proton-hole state is not known for N > 40. In 71Cu two 7/2- states around 1 MeV are candidates to be a proton-hole. The experiment at GANIL took place in March 2011. A secondary beam of 72Zn at 38 AMeV was produced by fragmentation and purified through the LISE spectrometer. The transfer reaction in inverse kinematics was studied with the MUST2 detectors plus four 20 µm silicon detector to identified the 3He of low kinetic energy. The excitation spectrum of 71Cu was reconstruct thanks to the missing mass method and the angular distributions were extracted and compared with a reaction model using the DWUCK4 and DWUCK5 code. From this work no states have been populated around 1 MeV concluding that the centroid of the πf7/2 lies at higher excitation energy. We then remeasured the single-particle strength in 69Cu in the corresponding (d,3He) reaction at Orsay in March 2013 in order to extend the existing data where 60% of the πf7/2 strength is missing and make sure that there is a consistent analysis of spectroscopic factors between both isotopes in order to well understood and well quantify the evolution of the f7/2 orbital when we start filling the vg9/2 orbital. In this second experiment we have performed the reaction in direct kinematics using a deuteron beam at 27 MeV provided by the tandem and a target of 70Zn of 18.7 µg/cm2. In this work we were able to extract three new angular distributions and we have measured a new part of the_πf7/2 strength. Finally in order to interpret the results we have obtained from those two experiments, state-of-the-art shell-model calculations have been carried out in collaboration with the Strasbourg group using the Antoine code. The valence space consists in a core of 48Ca with the valence orbitals for protons f7/2, p3/2, f5/2, p1/2 and the orbitals p3/2, f5/2, p1/2, g9/2, d5/2 for neutrons. The calculations have been done allowing 8p-8h and show that the strength is indeed at high energy and no f7/2 proton-hole state lies around 1 MeV in 71Cu.