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Ground state properties of nuclei such as the mass, nuclear angular and momentum lifetime reveal a nucleus’ fundamental structure. These properties are explored through high-precision Penning-trap mass spectrometry (Georg Bollen, David Morrissey), complementary time-of-flight mass measurements of very short-lived nuclei (Hendrik Schatz), high-precision measurements of nuclear moments (Paul Mantica), and beta-decay half-life measurements (Sean Liddick).
Several experimental programs at the NSCL are exploring the nuclear single-particle structure (nuclear shell structure) and are determining the way nucleons fill the available energy levels. Direct nuclear reaction studies combined with in-beam gamma-ray, charged-particle and neutron spectroscopy (Alexandra Gade, Wolfgang Mittig, Betty Tsang, Remco Zegers) have a large impact in this field, and are typically carried out in close collaboration with the local theoretical nuclear physics group that focuses on nuclear structure (Alex Brown, Morten Hjorth-Jensen) and nuclear reaction theory (Filomena Nunes). As part of the understanding of the evolution of nuclear shell closures, that is the “magic” numbers, the deformation of the nucleus, and its rotational, vibrational and (phase) translational behavior are studies in a broad program of measurement of excited state energies (Alexandra Gade, Sean Liddick), quantification of the physical shape from transition matrix elements determined via Coulomb excitation (Alexandra Gade), and precision measurements of excited-state lifetimes (Hironori Iwasaki).
As the number of nucleons approaches the physical limit called the “dripline”, exotic nuclear behavior such as extended shapes and even neutron halo structures signal significant changes in the shell structure. At the NSCL, the discovery of the most exotic nuclei (David Morrissey, Brad Sherrill, Michael Thoennessen) is followed up with detailed spectroscopy of exotic, neutron-unbound systems (Artemis Spyrou, Michael Thoennessen) and proton-emitting states (Sean Liddick, Hendrik Schatz) with in-flight spectroscopy and with detailed decay studies.
Experimentalists and theorists also work together at the NSCL to explore the fundamental forces that hold a nucleus together. Some researchers work to further our understanding of the Nuclear Equation of State (Wolfgang Bauer, Betty Tsang) and its isospin dependence (/ourlab/directory/profile/westfall). One way to get to the heart of nuclear matter is to smash it together to see what happens in nuclear collisions (Bill Lynch). Another way is to excite what is called giant resonances for systems far from stability (Remco Zegers, Wolfgang Mittig). In addition, theoretical work includes energy-density functional that are being used to predict and understand the equation of state and its isospin depedence (Scott Bogner, Alex Brown, Pawel Danielwicz), effective field theory and density functional theory (Scott Bogner), and many body theory of how nucleons interact (Filomena Nunes).
Mesoscopic physics deals with the forces and interactions of finite sets of objects down to the size of an atom. Rather than following the rules of classical mechanics, these sets are subject to quantum mechanics. At the NSCL, the Theory Group is studying the systems and equations that describe quantum many-body physics and quantum chaos at the mesoscopic level (Vladimir Zelevinsky).