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).
We are looking for new graduate students. Research Assistant (RA) positions are available.
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, contact our faculty (see Personnel → Faculty). 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
CeBrA demonstrator commissioned at FSU SE-SPS
A highly selective experimental setup for particle-γ coincidence experiments at the Super-Enge Split-Pole Spectrograph (SE-SPS) of the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University (FSU) using fast CeBr3 scintillators for γ-ray detection has been commissioned. A new publication reports on the results of characterization tests for the first five CeBr3 scintillation detectors of the CeBr3 Array (CeBrA) with respect to energy resolution and timing characteristics. Results from the first particle-γ coincidence experiments successfully performed with the CeBrA demonstrator and the FSU SE-SPS are also presented. The new setup enables very selective measurements of γ-decay branching ratios and particle-γ angular correlations using narrow excitation energy gates, which are possible thanks to the excellent particle energy resolution of the SE-SPS. In addition, nuclear level lifetimes in the nanoseconds regime can be determined by measuring the time difference between particle detection with the SE-SPS focal-plane scintillator and γ-ray detection with the fast CeBrA detectors. Selective excitation energy gates with the SE-SPS exclude any feeding contributions to these lifetimes. This research was supported by the National Science Foundation (NSF), United States under Grant No. PHY-2012522 (WoU-MMA: Studies of Nuclear Structure and Nuclear Astrophysics) and by Florida State University, United States.
CLARION2+TRINITY setup commissioned
A new Compton-suppressed HPGe and charged-particle array, CLARION2-TRINITY, has been commissioned at the FSU John D. Fox Laboratory in collaboration with Oak Ridge National Laboratory. The TRINITY charged-particle array is comprised of 64 Cerium-doped Gadolinium Aluminum Gallium Garnet (GAGG:Ce) crystals configured into five rings spanning 7–54 degrees, and two annular silicon detectors that can shadow or extend the angular coverage to backward angles with minimal γ-ray attenuation. GAGG:Ce is a non-hygroscopic, bright, and relatively fast scintillator with a light distribution well matched to SiPMs. Count rates up to 40 kHz per crystal are sustainable. Fundamental characteristics of GAGG:Ce were measured and presented in this article, including light- and heavy-ion particle identification (PID) capability, pulse-height defects, radiation hardness, and emission spectra. The CLARION2 array consists of up to 16 Compton-suppressed HPGe Clover detectors configured into four rings (eight HPGe crystal rings) using a non-Archimedean geometry that suppresses back-to-back coincident 511-keV gamma rays. The entire array is instrumented with 100- and 500-MHz (14 bit) waveform digitizers which enable triggerless operation, pulse-shape discrimination, fast timing, and pileup correction. Two examples of experimental data taken during the commissioning of the CLARION2-TRINITY system are also presented: a PID spectrum from 16O+18O fusion-evaporation, and PID and Doppler-corrected γ-ray spectra from 48Ti+12C Coulomb excitation.
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.
Recent News and Highlights
NSF MRI funding for CeBrA
Professors Lewis A. Riley from Ursinus College, Andrea Richard from Ohio University, and Mark-Christoph Spieker from Florida State University have received a $721,072 Major Research Instrumentation grant from the U.S. National Science Foundation to complete the Cerium Bromide Array (CeBrA) for particle-gamma coincidence experiments at the FSU SE-SPS of the John D. Fox Laboratory. The grant allows the team to add nine additional CeBr3 detectors to the current array of five, paving the way for selective nuclear-structure experiments and collaborative physics research with other institutions. Follow the links to read the announcements by Ursinus College and Florida State University.
Fox Lab awarded $9M grant by NSF
The Fox Laboratory has received a USD 9 million grant from the National Science Foundation to continue its cutting-edge research in nuclear physics and nuclear astrophysics. The grant supports the operation of the on-campus John D. Fox Accelerator Laboratory and the research programs of Professors Ingo Wiedenhoever (PI), Sergio Almaraz-Calderon (Co-PI), Paul Cottle (Co-PI), Mark-Christoph Spieker (Co-PI), Samuel Tabor (Co-PI), and Vandana Tripathi (Co-PI). The award abstract and information can be found here.
Piekarewicz co-organizes Talent School at ECT*
The DTP/TALENT 2024 School on Nuclear Theory for Astrophysics took place from July 15 to August 2, 2024 at the ECT* in Trento, Italy. FSU professor Jorge Piekarewicz was one of the main organizers and lecturers. The goal of the school was to provide the attendees with high level training on nuclear physics and nuclear astrophysics from various perspectives that include the Equation of State (EOS), neutron star mergers, and supernovae – and their combined impact in spearheading the brand new era of multi-messenger astronomy. In addition to Professor Piekarewicz, Almudena Arcones, Bruno Giacomazzo, as well as other experts in the various fields of relevance to the school were among the key lecturers. For more information, click here.
Wiedenhoever named Distinguished Research Professor
Florida State University has bestowed the title of Distinguished Research Professor on four outstanding faculty members for their exemplary research productivity and contributions to their fields. "Outstanding national and international scholarly output and creativity is a cornerstone of a thriving research enterprise," said Vice President for Research Stacey S. Patterson. "I am thrilled to be able to recognize four individuals as Distinguished Research Professors this year who model exceptional performance and extraordinary contributions to their fields." The Distinguished Research Professor award recognizes outstanding research and/or creative activity of eligible Florida State University faculty currently at the rank of full professor. Among the four 2024 recipients of the Distinguished Research Professor Award is Fox Laboratory Director Professor Ingo Wiedenhoever. Congratulations! Read more here.
Fox Lab student selected for student highlight
The FSU College of Arts and Sciences has selected Ana Pereira, a third year undergraduate in the Department of Physics, for a student highlight. Ana works with Professor Tripathi on an undergraduate research project on induced fission. Ana has presented their findings at FSU's 2024 Undergraduate Research Symposium and during the 2024 President’s Showcase of Undergraduate Research Excellence. Read more about Ana's spotlight interview and their participation in the 2024 President’s Showcase.
Fox Lab feature on Fox13 Tampa Bay
Professors Almaraz-Calderon, Cottle, and Wiedenhoever recently talked with "breakthroughs in science" host Craig Patrick for his segment on Fox13 Tampa Bay. The feature, which also mentions the planned collaboration with Mayo Clinic to develop improved methods of treating cancer, can be found here.
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.