Session LP: Nuclear Structure: A=40-70

Study of $^{40}$Ar$(p, p)$ resonance scattering using the AT-TPC and discussion of the single-particle limit

Isobaric resonances are important observations to investigate neutron single-particle states using the isospin symmetry of the nuclear force. These analog resonances are regularly observed in the excitation functions of proton elastic scattering. The resonance elastic scattering $^{40}$Ar($p,p$)$^{40}$Ar was carried out using the Active Target Time Projection Chamber (AT-TPC) in inverse kinematics, taking advantage of its capability to measure the scattered protons as the beam slows down in the gas. Pure hydrogen gas was used as the target as well as the tracking media. The preliminary result shows consistency compared to the previous $^{40}$Ar($p,p$)$^{40}$Ar measurements as well as the $^{40}$Ar$(d,p)$ transfer reaction done in normal kinematics. The proton partial width is related to the $S$ by its ratio to the single-particle width, which is usually estimated from the R-matrix formalism using the Breit-Wigner limit. A more realistic approach is to calculate the single-particle width of individual $(l,j)$-values within the Wood-Saxon potential. In yet another approach, $S$ is deduced by using the bound neutron wave function in the isobaric analog nuclei. These different ways to determine the single-particle width and the spectroscopic factors are compared and discussed.   

Charge radius of neutron deficient $^{\mathrm{54}}$Ni and constraints on slope parameter $L$ in the neutron equation of state

The charge radius of $^{\mathrm{54}}$Ni was determined using collinear laser spectroscopy at the BEam COoling and LAser spectroscopy facility. The $^{\mathrm{54}}$Ni radius is critical to determine the slope $L$ of symmetry energy in the nuclear equation of state. The linear correlation between the difference of charge radii of mirror nuclei $\Delta R_{mirr}$ and $L$ is used to set constraint on $L$ using the charge radii of proposed $^{\mathrm{54}}$Ni and its mirror partner $^{\mathrm{54}}$Fe, whose radius is also known. Details of the experiment and the progress of data analysis will be discussed.   

Visualizing Patterns in Nuclei with the Advanced Cross-Variable Plot

The Evaluated Nuclear Structure Data File (ENSDF) provides recommended data on 3,350 nuclei which have been studied experimentally. The National Nuclear Data Center (NNDC) at Brookhaven National Laboratory maintains several web applications that allow users to query and display this data. In order to help visualize patterns across this wide range of nuclei, we have developed the Advanced Cross-Variable Plot. This web page allows users to plot up to 35 nuclear observables as functions of each other. Observables currently available include Q values, excitation energies, transition strengths, half-lives, and fission yields. Because of its connection to the ENSDF database, the Cross-Variable Plot can graph these patterns across all known nuclides as a user requests them. This makes it capable of illustrating known patterns as well as searching for patterns yet to be found. By implementing these functions, the NNDC hopes to make the Cross-Variable Plot a useful tool for education and future research. Work sponsored by the Office of NP, Office of Science of the U.S. DOE under Contract No. DE-AC02- 98CH10886   

Nuclear Excitation via Electron Capture with TITAN

Nuclear Excitation via Electron Capture (NEEC) is the inverse process of internal electron conversion, where a free electron is captured into an atomic vacancy simultaneously exciting the nucleus to a higher-energy state. This process occurs naturally in hot astrophysical environments, and can excite nuclei in these isomeric states to shorter-lived states that would decay at a much faster rate than under terrestrial conditions, thus affecting reaction flows or survival rate of nuclei. Since NEEC is a resonant process, experimental access in the lab to study these cases requires strong atomic charge-state control over the sample, as well as careful selection and preparation of nuclear states that may be compatible with efficient electron recombination. Using an open-geometry electron beam ion trap (EBIT) in the TITAN experiment at the TRIUMF facility we are able to perform these studies with a high level of control and sensitivity. In this talk I will discuss the experimental concept, cases that we plan on studying in the near future, simulation results, as well as current and ongoing upgrades being made to the TITAN system.   

Spectroscopy of $^{47}$Sc and $^{48}$Sc through fusion evaporation

Excited states in in ${47,48}$Sc have been populated following the fusion-evaporation of $^{14}$C at 36 MeV impinged on a thin $^{36}$S target with a Ag backing at the John D. Fox Superconducting Laboratory at Florida State University. The evaporation channels were selected with a zero degree particle telescope while emitted gamma radiation was detected with a mixed array of Clover and single coaxial HPGe detectors. The observed level schemes of both 47,48Sc will be presented from coincident data. Preliminary angular distributions of observed states will also be presented. Results will be discussed and contrasted against single particle shell model results.   

Accurate nuclear charge radii measurements of neutron-deficient nickel isotopes

Charge radii of neutron deficient $^{\mathrm{54,55,56}}$Ni isotopes have been determined at the BEam COoler and LAser spectroscopy facility at NSCL to address the soft nature of doubly-magic $^{\mathrm{56}}$Ni. A novel approach was taken to precisely calibrate the Ni beam energy, which allowed us to accurately measure the isotope shifts relative to stable $^{\mathrm{60}}$Ni, from which the charge radii were deduced. Details of the calibration procedure and the obtained charge radii will be discussed.   

Triple Shape Coexistence in Stable $^{64}$Ni

In a tour de force involving 4 experiments at 4 different laboratories, an unexpectedly-complex landscape of triple shape coexistence was established in the stable, semi-magic $^{64}$Ni nucleus. For the first time, an excited $2^+$ state was also found in the prolate minimum. Shell model calculations, performed with significantly extended basis vector space, provided a microscopic understanding of the results and of the evolution in excitation energy of the prolate minimum across the $N=40$ sub-shell gap, and highlighted the impact of the monopole interaction and its variation in strength with increasing $N$.   

Evolution of the Z=20 gap in neutron-rich Ca isotopes

In recent years, neutron-rich Ca isotopes have been studied extensively, both theoretically and experimentally, as this is a region where structure can have a dramatic influence on the location of the neutron dripline. Large-space ab-initio calculations based on NN+3N forces predict that the dripline could extend as far as $^{70}$Ca. However, recent data reveal deficiencies in theoretical predictions which reveal that extrapolating to the dripline may prove unreliable For example, an anomalously large charge radii was measured in $^{50,52}$Ca relative to $^{48}$Ca which challenges the doubly-magic nature of $^{52}$Ca. I will report on the results of an experiment performed at the NSCL with GRETINA to determine the proton single-particle occupancies using the (d,n) proton transfer reaction on $^{50}$Ca to states in $^{51}$Sc.