Nuclear Structure Group Research

The nuclear structure group has a diverse array of research interests. A summary of each group member's current research focus can be found below.

	Rick Casten (D. A. Bromley Professor of Physics) My research interests focus on the twin themes of complexity and simplicity in the structure of atomic nuclei: that is, understanding, through experiment and theory, how these complex many-body quantal, femtoscale objects can be understood in terms of their ingredients (nucleons, their interactions, quantum mechanics, the Pauli and Uncertainty Principles) and, conversely, understanding the astonishingly simple and regular properties that these highly interacting systems display. The first approach -- complexity out of simple ingredients -- is the realm of understanding the nucleus microscopically on the femtoscale. The second -- how simplicity emerges in complex systems -- is the province of a macroscopic perspective grounded in symmetries and a geometrical approach to nuclear shapes. Both approaches are amenable to experimental probes. My research also includes a significant interpretative and theoretical component. My recent interests are in first order quantal phase transitions in the shapes of atomic nuclei as a function of nucleon number, testing and refining the new concept of Critical Point Symmetries that describe nuclei at the critical point of the phase transition and in measuring and understanding the proton-neutron interactions that, microscopically, drive the evolution of structure with nucleon number. Research Page \| Contact Information
	Andreas Heinz (Assistant Professor) I am working on understanding the production and structure of heavy nuclei, using mostly SASSYER, a gas-filled recoil separator, together with a number of other detectors. The physics I am interested in reaches from a deeper understanding of collective motion of nuclear matter to the evolution of nuclear structure at large proton numbers to the question where the periodic table ends. Research Page \| Contact Information
	Volker Werner (Assistant Professor) I am interested in nuclear structure properties which relate to the proton neutron degree of freedom. These are proton-neutron symmetric (pn in phase) and mixed-symmetric (pn not in phase) excitations which are sensitive to the interactions between the two species. These interactions have direct consequences on many other nuclear properties and manifest themselves in collective structures (vibrational, rotational) in the deformation of nuclei and the quantum shape phase transition between nuclei of different deformation. Another domain of pn interactions can be explored in nuclei with similar numbers of protons and neutrons, presenting a testing ground for the principle of isospin. The main method used is gamma-spectroscopy with germanium detectors, in most cases in coincidence with each other, and often with detected outgoing particles, as well. Research Page \| Contact Information
	Tan Ahn (Postdoctoral Research Associate) My current research interest is investigating the evolution of one-phonon mixed symmetry states in the mass 90 and 130 regions. The change in the properties of these states as a function of nucleon number will give important constraints on the parameters in the Interacting Boson Model and point to the underlying physical mechanisms that produce these changes. Coulomb excitation, the Doppler Shift Attenuation method, and angular correlation measurements are some of the techniques used to experimentally identify mixed-symmetry states. My current nucleus of interest is ⁹⁶Mo. Contact Information
	J. Russell Terry (Postdoctoral Research Associate) At low excitation energies, atomic nuclei exhibit structure that can be heavily influenced either by the motion of one or few nucleons or by the highly-correlated collective motion of a large number of nucleons. My research interests encompass both of these regimes. From the perspective of single-particle motion, my research interests have focused on quantifying changes in nuclear shell structure in increasingly unstable nuclei and measuring the single-particle structure of nuclear ground states for comparison with modern shell model calculations. From the perspective of collective motion, my research interests are currently focused on a class of low-lying excited states called mixed symmetry states in which some protons and neutrons within the nucleus do not move in phase. Contact Information
	Gabriela Ilie (Postdoctoral Research Associate) Contact Information
	Robert Casperson (Graduate Student) I am currently involved in the search for low-lying mixed symmetry states in ¹⁴⁰Nd. I will be investigating the role of quadrupole and eventually hexadecapole degrees of freedom in these states using the Interacting Boson Model 2 with g-bosons. Contact Information
	Aaron Mertz (Graduate Student) I am interested critical-point symmetries, which offer a classification of states and analytic expressions for observables in regions where the nuclear structure in the geometric model changes most rapidly. Specifically, I am examining candidate nuclei experimentally for evidence of the critical-point symmetry X(5). I will be on leave during the 2007-2008 academic year to study at the University of Oxford. Contact Information
	Jing Qian (Graduate Student) I am interested in decay spectroscopy of very heavy and superheavy nuclei produced by fusion-evaporation reactions. Currently I am working on ²⁵⁷Rf and extracting single particle structure from the isomer decay spectroscopy. The data will be used to test predictions of various models often used to predict the location of the next proton shell closure in the heaviest nuclei. Contact Information
	Elizabeth Williams (Graduate Student) My work is focused on two different types of transitional behavior in the nuclear landscape. The first, which I approach from a primarily theoretical perspective, is quantum phase transitional behavior of finite-sized nuclear systems in the large boson limit of the Interacting Boson Model. The second, which is experimental, is a beta-decay study of low-lying mixed symmetry states in ¹⁴⁰Nd. Home Page \| Contact Information
	Ryan Winkler (Graduate Student) My research interests include a variety of topics in nuclear structure physics. Current projects range from the use of the gas-filled separator SASSYER in the study of excited states in neutron-deficient Thorium isotopes to a systematic survey of low-spin states of well-deformed and transitional even-even nuclei as part of a collaboration with the Technical University of Munich. Contact Information
	Mason Marshall (Undergraduate) Contact Information
	Axel Schmidt (Undergraduate) My research at WNSL has encompassed sub-pecosecond life-time measurements to identify nuclear excited states with mixed-symmetry, the observation of E0 transitions using conversion electron spectroscopy, and the evolution of structure along the N=126 shell closure. Currently I am working with the gas-filled recoil separator SASSYER to study structure in proton-rich, N=126 nuclei. Contact Information
	Mallory Smith (Undergraduate) Currently, my research interests include quadrupole shape-phase transitions in the rare earth, midshell region. The rotational nuclei on the deformed side of this phase transition exhibit deviations from the rigid rotor model, which may be explained collectively in terms of centrifugal stretching or band mixing. Electromagnetic transitions from well-deformed nuclei beyond the phase transition allow a measurement of the deformation parameter. This parameter provides proof that these nuclei do not remain rigid, but stretch the faster they rotate. These calculations provide a sensitive test of new analytical models that take into account the deviations from the rigid rotor. Contact Information