Studying Atomic Nuclei while Reaching for the Stars
Exploring the synergy between nuclear physics and astrophysics has always been a core mission of nuclear science. Florida State University hosts strong groups in experimental and theoretical low-energy nuclear physics, as well as in astrophysics and astronomy, which work synergetically to tackle the open questions at the crossroads of these disciplines. The programs are funded by the Department of Energy (DOE) and the National Science Foundation (NSF). FSU plays a major role in the FRIB Theory Alliance. Besides performing experiments at different national and international facilities, the experimental nuclear physics group runs the John D. Fox Superconducting Linear Accelerator Laboratory located on the FSU campus. Operations of the laboratory are funded through the NSF. The Fox Laboratory is part of the Association for Research with University Nuclear Accelerators (ARUNA) and of the Center for Excellence in Nuclear Training and University-Based Research (CENTAUR).
Graduate Studies in Nuclear Structure and Nuclear Astrophysics
Become a part of our team. Exciting research projects are waiting for you. To find out more, visit our "Research" page. To apply as a gradudate student in the Physics Program at Florida State University, click here.
FSU graduates talk about their graduate-research experience at the Fox Lab.
Dr. Maria Anastasiou (Supervisor: I. Wiedenhöver)
Dr. Kalisa Villafana (Supervisor: M. Riley)
Featured Research
Measurement of the 25Al(d,n)26Si reaction and impact on the 25Al(p,γ)26Si reaction rate
25Al(p,γ)26Si reaction is part of a reaction network with impact on the observed galactic 26Al abundance. A new determination of the proton strength of the lowest l=0 proton resonance in 26Si is required to more precisely calculate the thermal reaction rate. To this end, the 25Al(d,n)26Si proton-transfer reaction is measured in inverse kinematics using an in-flight radioactive beam at the RESOLUT facility. Excitation energies of the lowest 26Si proton resonances are measured and cross sections are determined for the lowest l=0 resonance associated with the third 3+ state at 5.92(2) MeV. Coupled reaction channels calculations using fresco are performed to extract the l=0 spectroscopic factor for the third 3+ state. The proton width for the third 3+ state in 26Si is determined to be Γp=2.19(45) eV and the (p,γ) resonance strength for the third 3+ state is extracted as 0.026(10) eV. This resonance dominates the 25Al(p,γ)26Si reaction rate above 0.2 GK. FSU graduate student Eli Temanson published these results with his collaborators in Physical Review C.
Bayesian refinement of covariant energy density functionals
The last five years have seen remarkable progress in our quest to determine the equation of state of neutron rich matter. Recent advances across the theoretical, experimental, and observational landscape have been incorporated in a Bayesian framework to refine existing covariant energy density functionals previously calibrated by the properties of finite nuclei. In particular, constraints on the maximum neutron star mass from pulsar timing, on stellar radii from the NICER mission, on tidal deformabilities from the LIGO-Virgo collaboration, and on the dynamics of pure neutron matter as predicted from chiral effective field theories have resulted in significant refinements to the models, particularly to those predicting a stiff symmetry energy. Still, even after these improvements, it is challenging to reproduce simultaneously the neutron skin thickness of both 208Pb and 48Ca recently reported by the PREX/CREX collaboration using state-of-the-art energy density functional theory. FSU graduate student Marc Salinas published these results in Physical Review C.
Hexadecapole deformation in 74,76Kr
In the Ge-Sr mass region, isotopes with neutron number ≤ 40 are known to feature rapid shape changes with both nucleon number and angular momentum. To gain new insights into their structure, inelastic proton scattering experiments in inverse kinematics were performed on the rare isotopes 74,76Kr. This work focuses on observables related to the 4+ states of the Kr isotopes and, in particular, on the hexadecapole degree of freedom. By performing coupled-channels calculations, hexadecapole deformation parameters were determined for the 4+ states of 74,76Kr from inelastic proton scattering cross sections. Two possible coupled-channels solutions were found. A comparison to predictions from nuclear energy density functional theory, employing both non-relativistic and relativistic functionals, clearly favors the large, positive solutions. These values are unambiguously linked to the well deformed prolate configuration. Given the trend, established in this work, it appears that hexadecapole deformation parameters could provide a sensitive measure of the nuclear shell structure. Dr. Spieker and his collaborators published this work in Physics Letters B.
β- decay of exotic P and S isotopes with neutron number near 28
β- decay of very neutron-rich isotopes of P and S, studied at the National Superconducting Cyclotron Laboratory using the Beta Counting Station consisting of a Double Sided Strip Detector surrounded by clovers detectors for observing delayed γ transitions, is reported here. β-decay half-lives and delayed neutron emission probabilities were extracted for 42,43,44P and 44,46S by analyzing spatial and temporal correlations between implants and decay events in the Si detector with further coincidence with γ transitions. Detection of delayed γ rays allowed for the identification of negative-parity 1p1h states in 42S for the first time, also constraining the parent (42P) spin/parity to 2− or 3-. For the most exotic isotope studied, 46S, no strong γ transition was observed unlike lighter even-even S isotopes, thus implying the shift of Gamow-Teller strength distribution to higher energies. Comparison of experimental observations to detailed shell-model calculations using the SDPFSDG-MU interaction allowed us to infer the importance and role of first forbidden β transitions as the neutron number approaches and then exceeds N=28. Dr. Tripathi and her collaborators published this work in Physical Review C.
The puzzle of octupole collectivity in the Ge-Kr mass region
Enhanced octupole collectivity is expected in the neutron-deficient Ge, Se, and Kr isotopes with neutron number N=40 and has indeed been observed for stable 70,72Ge. Shape coexistence and configuration mixing are, however, a notorious challenge for theoretical models trying to reliably predict octupole collectivity in this mass region, which is known to feature rapid shape changes with changing nucleon number and spin of the system. To further investigate the microscopic configurations causing the prolate-oblate-triaxial shape transition at A=72 and their influence on octupole collectivity, the rare isotopes 72Se and 74,76Kr were studied via inelastic proton scattering in inverse kinematics using GRETINA, the S800 spectrograph, and the NSCL-Ursinus LH2 target. While significantly enhanced octupole strength of about 32 Weisskopf units (W.u.) was observed for 72Se, only strengths of about 15 W.u. were observed for 74,76Kr. In combination with existing data, the new study by Dr. Spieker and his collaborators clearly questions a simple origin of enhanced octupole strengths around N=40. The work was published in Physical Review C.
Couplings to continuum states jump-starting deformation in 28,29F
Recent experiments showed that, unexpectedly, the neutron-rich isotope 28F belongs to the so-called N=20 island of inversion (it has N=19), and that the isotope 29F has a halo structure in its ground state. These surprising findings were explained By Dr. Fossez and his collaborator Dr. J. Rotureau using the density matrix renormalization group (DMRG) method for open quantum systems, which revealed that continuum couplings enhanced the occupation of the 0p3/2 neutron shell, responsible for the halo in 29F, which in turn enhanced couplings with the 0f7/2 neutron shell leading to quadrupole deformation in 28F and the negative parity observed.
Elusive resonance in 11B uncovered
FSU graduate student Eilens Lopez-Saavedra and her collaborators have observed the elusive near-threshold resonance in 11B. The 10Be(d,n)11B → 10Be+p experiment was performed at the Fox Lab with RESOLUT and a dedicated detector setup in inverse kinematics. The now confirmed presence of the state (resonance) is an important step toward understanding the excessively large beta-delayed proton-decay branch of 11Be, which had previously triggered lots of speculations including exotic decays of the neutron. The results were published in Physical Review Letters.
Resolution of a long-standing discrepancy in the 17O+12C fusion excitation function
Research by recent FSU graduate Dr. Benjamin Asher used the 'Encore' active target detector, built during his PhD, to solve a long-standing discrepancy in the fusion excitation function of the 17O+12C system. The unique properties of Encore allowed to measure a large portion of the fusion excitation function with a single beam energy, avoiding normalization issues that are usually present in this type of measurements. Ben's research found strong oscillations which have not been observed before in odd-even systems.
Single-particle structure of the PDR and its implications for nuclear astrophysics
A collaboration involving Dr. Spieker (FSU) has for the first time probed the fine structure of the pygmy dipole resonance (PDR) in a (d,pγ) experiment performed at the University of Cologne. The results were published in Physical Review Letters [M. Weinert et al., Phys. Rev. Lett. 127, 242501 (2021)]. Surprisingly, only the lower group of 1- states was populated in the one-neutron transfer reaction. This experimental result could, however, be reproduced using detailed QPM wavefunctions as input for careful reaction calculations. The new results challenge models using the dipole response as input to calculate (n,γ) rates in stellar environments.
Recent News and Highlights
Cottle on Florida's STEM education
Paul Cottle was interviewed by 20-time Emmy winner Craig Patrick of Tampa Bay's Fox 13 for his show "Money, Power and Politics" about Florida's shortcomings in preparing high school students for college STEM majors, including physics, engineering and computing. The segment was broadcast in March 2024 and can be found on YouTube. Cottle was also invited by the Palm Beach County School District (the nation's tenth largest school district with about 200,000 students) to speak to high school students about how to best prepare for college majors in STEM fields, including physics, engineering and computing. Professor Cottle spoke to a live audience at John I. Leonard High School and reached many more through the district's live stream of the talk to high schools throughout Palm Beach County on March 14, 2024, which is available on YouTube.
New Long Range Plan for Nuclear Science
The United States Nuclear Science Advisory Committee (NSAC) released "A New Era of Discovery: The 2023 Long Range Plan for Nuclear Science". This new long range plan provides a roadmap for advancing the nation's nuclear science research programs over the next decade. The U.S. Nuclear Science community releases such a plan every 5-8 years highlighting the scientific opportunities of nuclear physics today to maintain world leadership. The document also explores the impact of nuclear science on other fields and applications of the research that benefit society. Science opportunities at the ARUNA laboratories, to which the Fox Lab belongs, were prominently featured.
Dr. Fossez receives NSF CAREER Award
Dr. Kevin Fossez has earned one of the most prestigious awards available to early career faculty members for his work in theoretical nuclear physics. He is a recipient of a 2023 Faculty Early Career Development Award, or CAREER Award, from the National Science Foundation for his work investigating how to better predict properties of new combinations of protons and neutrons at the limits of nuclear stability. “I am thrilled this award will provide funding for five years to pursue my work within a long-term perspective by building a research group and going deeper into certain problems, like challenging the common understanding of atomic nuclei by producing isotopes with a fleeting existence,” Fossez said. “It is also recognition that my work is valued by the scientific community, which is always appreciated.” Read more in this feature article.
Marc Salinas receives dean's award for doctoral excellence
FSU graduate student Marc Salinas, who works with Professor Piekarewicz, received the 2023 DEAN’S AWARD for DOCTORAL EXCELLENCE (DADE). The competitive award recognizes meritorious performance from doctoral students in the later phases of their program. Marc's research focuses on constraining the nuclear matter equation of state through the use of relativistic mean field theory and by incorporating information from nuclear experiments and neutron stars into a Bayesian framework.
Fox Lab alumnus featured in APS News
Fox Lab alumnus Jesus Perello Izaguirre has been featured in the FSU Spectrum magazine as well as in the American Physical Society (APS) News. Jesus joined FSU's graduate school program through the Department's Bridge program. At the Fox Lab, part of the U.S.’s Center for Excellence in Nuclear Training and University-Based Research (CENTAUR), Jesus worked alongside Prof. Sergio Almaraz-Calderon to better understand observations made by the NASA Fermi gamma-ray telescope orbiting in space that detected radioactive elements throughout the galaxy. After graduating in 2021, he accepted at postdoc position at Los Alamos National Laboratory. Read more about his story in the two feature articles.
Particle-gamma coincidences at SE-SPS
The Fox lab has completed the installation of CeBrA demonstrator for particle-γ coincidence experiments at the Super-Enge Split-Pole Spectrograph (SE-SPS) and connected upgrades to the beamline. The first particle-gamma experiments with the new CeBr3 gamma-ray detectors concluded successfully including experiments during the 2023 REU at the Fox Lab. The results of the commissioning experiments have been published in Nuclear Instruments and Methods in Physics Research Section A. FSU graduate student Alex Conley, working with Dr. Spieker, led the developments.
FSU research featured in DOE Science Highlights
The Department of Energy, Office of Science has recently featured research from our group in their Science Highlights. In December 2022, the work of Professor Jorge Piekarewicz was featured in an article titled "Building Bridges and Ladders in Astrophysics: Theory and Experiment Inform the Equation of State". Earlier in 2022, the Office of Science had chosen the work of our graduate student Eilens Lopez-Saavedra for a highlight: "Near-Threshold Resonance Helps Explain a Controversial Measurement of Exotic Decay in Beryllium-11". The results were obtained in collaboration between the groups of Professors Sergio Almaraz-Calderon, Alexander Volya and Ingo Wiedenhoever.
Elusive resonance in 11B
FSU graduate student Eileens Lopez-Saavedra and her collaborators have observed the elusive near-threshold resonance in 11B. The 10Be(d,n)11B → 10Be+p experiment was performed at the Fox Lab with RESOLUT and a dedicated detector setup in inverse kinematics. The now confirmed presence of the state (resonance) is an important step toward understanding the excessively large beta-delayed proton-decay branch of 11Be, which had previously triggered lots of speculations including exotic decays of the neutron. The results were published in Physical Review Letters.
FRIB Visiting Scholar 2022
The Facility for Rare Isotope Beams (FRIB) at Michigan State University has opened its doors holding the promise to reach the new frontiers of the nuclear chart. To perform the first user experiment with the FRIB Decay Station initiator (FDSi), Vandana Tripathi was selected as the award recipient for the 2022 FRIB Visiting Scholar Program for Experimental Science. Read more about the excitement around the first FRIB experiment and Vandana's award.