55 Co

1. 1.5mm Si CsI(Tl) 65μm Si • Spectroscopic Factors from Transfer Reactions with Radioactive Beams R. Shane1*, T. K. Ghosh2, A. Sanetullaev1 and M. B. Tsang1 For the HiRA Collaboration N=28 N=20 Experimental Setup 56Ni: An alluring nucleus The probe: Spectroscopic Factor Spectroscopic Factor (SF) quantifies the nature and occupancy of the single particle orbits in a nucleus. N=8 HiRA + S800 @NSCL d / 3He HiRA • 56Ni is outside the valley of stability and is doubly magic according to the Independent Particle Model (IPM) • In the shell model, the magic number 28 is the first shell that requires the introduction of a strong spin-orbit interaction • 56Fe is the most abundant heavy element in the universe, yet 56Ni is the first doubly-magic nucleus that is not stable • 56Ni is a “waiting point” nucleus in the astrophysical rapid proton (rp) capture process • Understanding the shell structure of this doubly-magic, N=Z=28 nickel nucleus is therefore of considerable interest for both nuclear structure and astrophysics Single-nucleon transfer reactions are a powerful tool to study single particle states. N=2 Target (p / d) IPM MCP's θ 56Ni Beam Φ To S800 Spectrograph Inverse kinematics at 37MeV/A, 80MeV/A 55Ni / 55Co (measure P,E,Φ) SF provides information on nuclear structure and is a key input for astrophysics calculations. S800 PID - 56Ni(d,3He)55Co 55Co High Resolution Array (HiRA) Reaction Model: (d/d)RM calculated from 3-body model with global optical potentials and standard geometry of n-wave functions. HiRA PID - 56Ni(d,3He)55Co S800 Spectrograph 3He Ground-state neutron SF of Ni isotopes Measurement of the SF is essential in calibrating the theoretical shell model of the nucleus. Results (p,d) @ 80.7 MeV/A (d,3He) @ 80.7 MeV/A Two possible shell structures of 56Ni: Proton Potential: Deuteron Potentials: Goal of experimental study ch = Chapel Hill 89 Phys. Rep. 201 (1991) 57 js = Johnson-Soper PRC 1 (1970) 976 pp = Perey-Perey ADNTD 17 (1976) • Study nucleon transfer reactions in inverse kinematics: • 56Ni(p,d)55Niat 37 MeV/A and 80 MeV/A to extract the neutron spectroscopic factorof 56Ni and also its energy dependence • 56Ni(d,3He)55Coat 80 MeV/A to extract the proton spectroscopic factor of 56Ni • These two reactions allow us to compare the neutron and proton SF in the f7/2 shell • Extracted spectroscopic factors are important benchmarks in evaluating different pf-shell model interactions that may be used to predict the structure of 78Ni, a major waiting point in the path of the r-process. gdp = GDP08 PRC 79 (2009) 024615 and ch=Chapel Hill 89 pp = Perey-Perey ADNTD 17 (1976) Inert core of 40Ca with 8 protons and 8 neutrons outside 3He Potentials: Deuteron Potentials: Differential Cross section [arb. units] Differential Cross section [arb. units] js = Johnson-Soper PRC 1 (1970) 976 bg = Bechetti-Greenlees ADNTD 17 (1976) 40 0 20 40 60 0 10 20 30 40 0 20 Inert core of 56Ni with 28 protons and 28 neutrons inside Lab Angle [degrees] Lab Angle [degrees] *Note: there seems to be a shift in angle between the data and calculations which is not yet understood Shape of calculation section depends on potentials. Best match to data is for CH89 (p), Perey-Perey (d), and Bechetti-Greenlees (3He). • Implications: • 56Ni is not a good core • Accurate description of Ni isotopes requires full model space with 40Ca core. • GXPF1A describes the data better than K3B interactions (p,d) @ 37 MeV/A SF is extracted by matching the magnitude of the calculated cross section to the data The value SFexp = 7 was determined for the f7/2 neutron from data at 37 MeV/A Summary The global OM potentials obtained from systematic analysis of (p,d) and (d,p) transfer reactions at low-energy do not seem to work at higher energy. Work on extraction of the neutron and proton SF from the higher-energy data, as well as a consistent framework for comparison to the low-energy results, is in progress. 1National Superconducting Cyclotron Laboratory, Michigan State Univ., East Lansing, MI 48824, USA 2Variable Energy Cyclotron Centre, 1/AF, Bidhannagar, Kolkata 700064, India * E-mail: shane@nscl.msu.edu