People

CENTAUR Directors:

Sherry J. Yennello, Program Director

 Prof. Sherry J. Yennello

Director of CENTAUR and Professor of Chemistry at Texas A&M University
Website

In the nuclear equation of state, the energy associated with an imbalance of neutrons and protons is termed the asymmetry energy. The density dependence of this quantity is currently the largest uncertainty. The Yennello Research Group focuses on further constraining this density dependence using heavy-ion collisions. Utilizing the K500 and K150 cyclotrons, heavy-ion projectiles are accelerated to up to 40% the speed of light and collided with stationary targets. These reactions are important for studying structure, chemical composition and the evolution of neutron stars and dynamics of supernovae explosions.
Lauren Heilborn, Managing Director & Science Coordinator

Lauren Heilborn


CENTAUR Faculty:

Aldo Bonasera, Texas A&M University
Aldo Bonasera

Aldo Bonasera
Website
Senior Research Scientist
Cyclotron Institute, Texas A&M University

Measuring Fusion Cross Sections in Plasmas
We presented for the first time a new and general method for measuring the astrophysical S factor of nuclear reactions in laser-induced plasmas and we applied it to 2H(d,n), 3He and 3He(d,p)α. The experiment was performed with the Texas Petawatt Laser, which delivered 150–270 fs pulses of energy ranging from 90 to 180 J to D2 or CD4 molecular clusters. We used scintillators to detect the 14.7 MeV proton coming from the fusion reaction. In more recent experiments we improved the technique to measure the plasma ion distribution and measured hard γ (less than 5 MeV) coming from the plasma. We prepared the CD4 cluster gas at the critical point of the liquid gas phase transition and let it expand in vacuum. We measured the range of the ions in the cold and hot regions of the plasma and the number of neutrons produced. We found that the initial correlations in the gas due to the phase transition influence the range and the number of fusions. We saw a good agreement with predictions using the Fisher’s model of 2nd order phase transitions. In these experiments the plasma is at relatively low density (of the order of 1018 cm-3) and the laser does not compress it. We have performed other experiments at SGII-Shanghi, China compressing solid CD2 target by means of 8 laser beams (Elaser about 16 kJ in 3 ns) in cylindrical symmetry. Different methods to measure the plasma ion distributions and the fusion reactions were used. From a preliminary analysis we found that the system gets compressed about 4000 times its initial value but the plasma temperature at maximum compression is rather low, of the order of 1 keV. The range seems to be orders of magnitude larger than predictions using SRIM. The final goal is to be able to measure the fusion cross sections in such extreme conditiimproving the detecting system.

 

Constrained Molecular Dynamics (CoMD) Model
Microscopic dynamical models such as the Constrained Molecular Dynamics (CoMD) model have been very successful in describing a large amount of data in fragmentation, fusion, fission and more recently in charge-exchange reactions. However, this approach and similar ones, fail in reproducing binding energies and other properties of light nuclei. Some aspect of clusterization and the possibility of Bose Einstein Condensation in nuclear dynamics are also not well described in the model. As a result the yield of α-particles in fragmentation reactions is underestimated and the binding energies of neutron rich (poor) nuclei are not well described in the model. The approach uses a Skyrme type force, which includes the symmetry energy term and a simplified three body potential. Pauli blocking is enforced as a constraint, which helps in saving CPU time while preserving general features of Fermions. In a recent version of CoMD we have implemented a second constraint to take into account the Heisenberg principle as well. Bosonic effects have also been included in the collision term for d-d and α-α collisions. We plan to introduce realistic three body forces (including Efimo-type potentials) and (i)spin-(i)spin interaction to reproduce the binding energies of d, t, 3He and α particles which were poorly described in the original model. We are also in the process of introducing 1s type forces. The requirement for the new forces is not just to reproduce properties of finite nuclei but also properties of nuclear (neutron) matter. These aspects are experimentally studied at Texas A&M. A strong collaboration with experimentalists has been fruitful in the past and we plan to keep this tradition going. Aspects of the competition between Fermionic and Bosonic degrees of freedom will be pursued. The production of superheavy nuclei and fission is also of interest as in previous works.

Greg Christian, Texas A&M University
Greg Christian

Greg Christian
Website
Assistant Professor
Department of Physics & Astronomy, Texas A&M University

Radioactive capture reactions–(p, γ), (n, γ), and (α, γ)–are important both for understanding nucleosynthesis in stellar environments and for national security. For many important reactions, the target nucleus is short lived. This makes direct measurements of the reaction rates extremely challenging, and in many cases impossible. As a result, indirect techniques must be used to understand the rates of these reactions experimentally. In this project, nucleon transfer reactions such as (d, p), (6Li, d), and (p, t) are used to populate and study the specific resonant states through which important radiative capture reactions proceed. In the experiments, a large-area, position-sensitive silicon detector array is combined with the MDM magnetic spectrometer and gamma-ray detectors to measure the spins, spectroscopic strengths, and branching ratios of these resonant states. From these measurements, theoretical techniques are used to indirectly determine the rate of the radiative capture reaction of interest and, in turn, to improve understanding of the nucleosynthesis or national security topic of interest. Improved technologies for detecting fast neutrons are important both for improving understanding of a variety of topics in basic and applied nuclear science. These include nuclear structure away from stability, nuclear astrophysics, measurements of prompt fission neutron cross sections, and detection of hidden WMDs. Current fast neutron detectors based on plastic or liquid scintillators are limited in both position and energy resolution, which in turn affects the quality of experiments for basic and applied nuclear science. This project will explore methods of improving the position sensitivity of fast neutron detectors by coupling plastic scintillators to pixelated photon detectors – SiPMs or PMTs. Analysis of the distribution of scintillation light at the various pixels will be used to triangulate the source of the light, and thus the neutron interaction point. In particular, techniques from the medical imaging community will be applied to fast neutron detection for the first time, with the promise to improve position sensitivity of fast neutron detectors to 1 cm or better, without a significant loss in timing/energy resolution, or in efficiency.

Jeremy Holt, Texas A&M University
Jeremy Holt

Jeremy Holt
Website
Assistant Professor of Physics
Texas A&M University

Microscopic nuclear structure and reaction theory has undergone a major transformation in the last decade with the development of chiral effective field theory, the low-energy realization of quantum chromodynamics. My research program utilizes "next-to-first principles" chiral two- and three-body forces to derive nucleon single-particle properties (momentum- and density-dependent isoscalar and isovector optical potentials, effective masses, and spectral functions) in order to improve modeling of neutron-capture reaction rates in r-process nucleosynthesis and particle transport in experimental heavy-ion collisions.

Scott Marley, Louisiana State University
Scott Marley

Scott Marley
Website
Assistant Professor of Physics
Louisiana State University

Prof. Marley is an experimental nuclear physicist interested the structure and decay properties of unstable atomic nuclei. Joined by a CENTAUR-supported graduate student, Marley will use transfer reaction experiments to study the structure of light-mass isotopes at the limits of β-stability. The group aims to improve knowledge of trends in the structure of light nuclei moving toward less bound systems and to test the most modern theoretical approaches to the nuclear many-body problem.

Ralf Rapp, Texas A&M University
Ralf Rapp

Ralf Rapp
Website
Professor of Physics
Texas A&M University

Photons emitted in heavy-ion collisions are particularly valuable probes to study the properties of the strongly interacting matter formed in heavy-ion collisions: once produced, they can escape the nuclear fireball without rescattering and thus probe its inner hot and dense regions. We will first compute the thermal photon emission rates for the temperatures and densities relevant for heavy-ion collisions in the Fermi energy regime. We will then implement these rates into transport calculations for the evolution of the fireball, by extracting local temperatures and densities. The calculated spectra will be compared to experiments to deduce the temperatures and densities reached in these reactions, and how the matter properties change as its isospin concentration is varied.

Anna Simon, University of Notre Dame
Anna Simon

Anna Simon
Website
Assistant Professor of Physics
University of Notre Dame

Stellar nucleosynthesis processes involve thousands of reactions for which the cross sections need to be described using theoretical models. For a wide variety of processes, e.g. p-, s- and r-process the nucleosynthesis path runs through heavy nuclei, thus statistical Hauser-Feshbach (HF) models can be applied to describe the cross sections. HF models requires as input, among others, g-strength (gSF) and level density (LD) functions, and optical model potential (OMP). A wide variety of models that describe these quantities (see e.g. TALYS code), results in cross sections predictions that can vary even by an order of magnitude, resulting in large uncertainties in network calculations of the nucleosynthesis processes.The Oslo method provides a well-established tool to extract the gSF and LD from experimental data. Such measurements allow for constraining the inputs for the HF models and as a result minimize the uncertainties in the network calculations. The Oslo-type experiments require simultaneous measurement of the γ rays and the excitation energy of the produced nucleus. This is typically done using scintillator detectors and particle telescopes. The Oslo-type experiments have shown that the gSF exhibits an unanticipated behavior at lower energies: the so-called upbend. This feature has been shown to exist in nuclei as heavy as 138La. However, the scintillators do not allow for extraction of the gSF below 1 MeV. Thus, for heavier nuclei, where the upbend shifts towards lower gamma-ray energies, the results from experiments using scintillator detectors are inconclusive, as they do not probe the gSF far enough.The STARLiTeR/HYPERION array at the Cyclotron Institute of Texas A&M University provides a unique environment to perform Oslo-type experiments using Compton suppressed clover detectors combined with a DE-E telescope. The Compton suppression of the gamma-detectors is a key to extending the lower limit of the gSF measurements even to 0.5 MeV, which unravels the features that could not be observed during traditional Oslo-type experiments. A recent experiment performed using the STARLiTeR array for 152,154Sm(p,d)151,153Sm revealed an upbend in the heaviest investigated nucleus so far.

Akram Zhanov, Texas A&M University
Akram Zhanov

Akram Zhanov
Website
Senior Research Scientist in Physics
Texas A&M University

Akram Zhanov is a senior scientist at the Texas A&M University Cyclotron Institute. His research focuses on advancing theory of low-energy nuclear reactions, neutron and proton radiative capture reactions, indirect methods in nuclear astrophysics, stellar nucleosynthesis, and few-body systems.

Sergio Almaraz-Calderon, Florida State University
Sergio Almaraz-Calderon

Sergio Almaraz-Calderon
Website
Assistant Professor of Physics
Florida State University

Dr.Calderon's research focuses on the study of nuclear interactions and how they influence astrophysical processes. His research interests include nuclear structure, nuclear reactions, nuclear astrophysics, stable and radioactive ion beams, and detector development.

Aurel Bulgac, University of Washington
Aurel Bulgac

Aurel Bulgac
Website
Professor of Physics
University of Washington, Seattle

Dr. Bulgac studies static and non-equilibrium dynamics of quantum many-body systems, typically strongly interacting fermions. Physical systems include atomic nuclei, the crust of neutron star crust, cold atom systems. Physical phenomena range from ground and excited state properties of such systems, energy density functionals, equation of state, thermodynamic properties, nuclear reactions, real-time fission dynamics, quantized vortices, their generation and their dynamics, incipient stages of quantum turbulence in fermionic superfluids. He develops and uses static and time-dependent density functional theory extended to fermionic superfluids, quantum Monte Carlo methods and other theoretical approaches, as well as their numerical implementation. Numerical calculations are performed typically on leading edge supercomputers, such a Summit (#1 on TOP 500) and Titan  (#9 on TOP 500) at ORNL, Piz Daint (#5 on TOP 500), at Swiss national Supercomputer Center, Lugano, Switzerland, and Tsubame at Tokyo Institute of Technology, Japan. His group uses GPUs programmed with CUDA on these supercomputers in order to  perform calculations on these supercomputers as close as possible to their peak capabilities. Many details can be inferred from his publication list and personal web page, where one can find links to talks, many videos, codes, and other pertinent information.

 

Dan Melconian, Texas A&M University
Dan Melconian

Dan Melconian
Website
Associate Professor of Physics
Texas A&M University, College Station

Precision measurements of the decays of radioactive nuclei produced by the cyclotrons are a powerful probe of the fundamental forces governing our universe. Using elegant techniques in "table-top" experiments both locally at the Cyclotron Institute as well as at other laboratories, our group aims to complement the efforts of our colleagues at larger facilities (such as the Large Hadron Collider) to search for physics beyond our current understanding as encapsulated in the Standard Model of particle physics.

Some of the main projects being pursued include measuring decay properties of unstable nuclei (lifetimes, branching ratios and masses) and angular distributions of the decay products of atoms and ions confined in magneto-optical and Penning traps. Our main endeavour within CENTAUR, with collaborators from Lawrence Livermore and Argonne National Laboratories, aims to improve our knowledge of how many fissions occur in a chain reaction. In particular, the fission products 147Nd and 156Eu (along with other long-lived isotopes) play a crucial role in science-based stockpile stewardship and nuclear forensics. The uncertainties on the γ-branching ratios measured for these isotopes currently compromise the usefulness of the existing data, which is what we are working to remedy. The γ-ray branching ratios of 147Nd and 156Eu are known to only 8%, hence leading to an 8% uncertainty in the fission-chain yield. The absolute γ-ray branching ratios for 147Nd and 156Eu are needed to 1–2% precision for national-security applications and to greatly improve the precision and reliability with which the number of fissions can be determined.

 


CENTAUR Post-Doctoral Researchers: 

Cody Parker, Texas A&M University

Cody Parker

Cody Parker is a postdoctoral research associate at the Cyclotron Institute in Prof. Greg Christian’s group. She is working with CENTAUR-affiliated graduate students and faculty on prototyping a new fast neutron detector. The goal of the highly-segmented design is to achieve position resolution of about 1 cm without sacrificing timing, energy resolution, or efficiency. A detector with these capabilities will be beneficial for applied nuclear science, such as measuring fission neutron cross sections or as a portal monitor. Basic nuclear physics will also be explored, including reactions relevant to nuclear astrophysics or neutron decay of isotopes off of the line of stability, such as 6He. You can download a poster of her research here.


CENTAUR Students:

Eames Bennett, Texas A&M University

Eames Bennett

Eames Bennett is a graduate student working with Dr. Greg Christian at the Texas A&M University Cyclotron Institute. His research focuses primarily on radioactive capture reactions and their role in stellar evolution. Bennett is currently analyzing data from a transfer reaction done in inverse kinematics using the TIARA array. You can download a poster of Bennett's research

.

 
Daniel Hoff, Washington University in St. Louis

Daniel Hoff

Daniel Hoff is a graduate student at Washington University in St. Louis. You can download a poster on Hoff's research

.

Shi Jin, University of Washington

Shi Jin 

Graduate Student in Physics at the University of Washington

Shi Jin is a graduate research assistant with Professor Aurel Bulgac in Department of Physics, University of Washington. Shi’s research includes the theoretical study of nuclear structure and dynamics using the density functional theory (DFT) and its time-dependent extension (TDDFT). His current project is the simulations of fission dynamics with TDDFT. You can download a poster on Jin's research

.

Thomas Onyango, Texas A&M University

Thomas Onyango

Thomas Onyango is a graduate student at Texas A&M University. Onyango graduated from the University of North Texas in 2018 with a B.S. in physics minors in both engineering technology and mathematics. His undergraduate thesis focused on possible entropy production from quantum mechanical measurements that would not be represented by thermodynamics. Onyango began studying Texas A&M during an REU for the Cyclotron Institute with Dr. Rapp in 2017 and began working in 2018. In his work with Dr. Rapp, Onyango assisted him with the parameterization of the rho meson spectral function in hot, dense matter. Currently under Dr. Rapp, Onyango is using Dr. Bonasera's transport codes to analyze Ca40-Ca40 collisions to analyze the evolution of fireballs over time and space.

Rachel Malecek, Louisiana State University
Rachel Malecek
 

Rachel Malecek is a graduate research assistant with Prof. Scott Marley. Malecek is interested in studying the structure and decay properties of light-mass, unstable atomic nuclei with transfer reaction experiments then testing modern theoretical approaches to the nuclear many-body problem. You can download a poster on Malecek's research

.

Jesus Perello, Florida State University

Jesus Perello

Jesus Perello is a graduate research assistant working with Sergio Almaraz Calderon at Florida State University. Perello worked on the development of a deuterated neutron detector array, CATRiNA, at John D. Fox Superconducting Linear Accelerator Facility for nuclear structure and nuclear astrophysics research. You can download a poster on Perello's research.

Cole Pruitt, Washington University in St. Louis

Cole Pruitt

Cole Pruitt is a PhD student in the Radiochemistry group at Washington University in St. Louis. His research includes measurement of neutron total cross sections on rare stable isotopes at the Los Alamos Neutron Science Center (LANSCE) and neutron elastic cross sections at the Triangle Universities Nuclear Laboratory (TUNL). Data from these experiments are valuable for constraining the isovector dependence of optical models such as the Dispersive Optical Model (DOM). In addition, Cole is generalizing the DOM for broad use across the chart of nuclides and applying newly-available techniques in machine learning to improve analysis of nuclear data. You can download a poster of Pruitt's research.

Elizabeth Rubino, Florida State University

Elizabeth Rubino

Elizabeth Rubino is a graduate student working under Dr.Sam Tabor at Florida State University's John D. Fox Superconducting Linear Accelerator Laboratory. Her studies include nuclear structure of 41^K and 41^Ca using gamma spectroscopy. You can download a poster on Rubino's research.

Benjamin Schroeder, Texas A&M University

Benjamin Schroeder

Mr. Schroeder is a member of Dan Melconian's research group at the Cyclotron Institute.  The Melconian group is developing TAMUTRAP, the largest Penning trap in the world, to be used for T=2 ß-delayed proton emission studies.  This will serve as a probe of the fundamental structure of the electroweak interaction in the Standard Model.  Mr. Schroeder is primarily working on the development of high energy resolution silicon detectors to detect the ßs and protons from these decays. You can download a poster on Schroeder's research.

Taylor Whitehead, Texas A&M University

Taylor Whitehead

Taylor Whitehead is a graduate student at Texas A&M University. His research focuses on deriving nucleon-nucleus optical potentials from high-precision chiral two- and three-body forces. Microscopic optical potentials do not depend on adjustable parameters and therefore may have greater predictive power for nuclear reactions involving unstable nuclei for which experimental data are unavailable. Nuclear optical potentials are an important input for calculations of neutron capture cross sections, which are vital for accurately describing astrophysical processes and nucleosynthesis. You can download a poster on Whitehead's research.

Dustin Scriven, Texas A&M University

Dustin Scriven

Dustin Scriven is a graduate student at Texas A&M University who works under Dr. Greg Christian at the TAMU Cyclotron Institute. In collaboration with others, he and his colleagues are working on the development of a highly segmented fast neutron detector. They hope to use this detector to investigate nuclear structure and processes for neutron and multi-neutron emission from nuclei. Dustin performs simulations for the detector and is also involved in prototyping. He is also interested in the deep relationship between nuclear physics and astrophysics. You can download a poster of his research here.


Graduated CENTAUR Students:

Brittany Abromeit, Pacific Northwest National Laboratory
Brittany Abromeit

Brittany Abromeit

Brittany Abromeit was a graduate research assistant with Dr. Sam Tabor, director of the accelerator laboratory at Florida State University. Abromeit's studies included the nuclear structure of 39Ar and 39P using gamma spectroscopy, at the John D. Fox Superconducting Linear Accelerator Laboratory and the National Superconducting Cyclotron Laboratory at Michigan State University. You can also download a poster on Abromeit's Research. Currently, she is a post-doctoral researcher in the Detection Systems group in the National Security Directorate at the Pacific Northwest National Laboratory, Washington.

Shi Jin, Amazon

Shi Jin 

Graduate Student in Physics at the University of Washington

Shi Jin was a graduate research assistant with Professor Aurel Bulgac in the Department of Physics at University of Washington. Shi’s research included the theoretical study of nuclear structure and dynamics using the density functional theory (DFT) and its time-dependent extension (TDDFT). His current project is the simulations of fission dynamics with TDDFT. He has gone on to a new job at Amazon. You can download a poster on Jin's research.

 


CENTAUR Affiliates:

Aaron Couture, Los Alamos National Laboratory
Aaron Couture

Aaron Couture
Website
Research Scientist in Physics
Los Alamos National Laboratory

Aaron Couture is engaged in the experimental study of neutron capture by hook or by crook. Neutron capture is responsible for the production of almost all of the observed elements heavier than iron. Nuclear waste transmutation concepts rely on neutron capture to reduce long-lived radionuclide inventories. Nuclear forenics relies on understanding neutron reaction networks. Where possible, these reactions are measured directly with neutron beam facilities such as LANSCE at Los Alamos. These measurements are complemented by nuclear structure studies on rare isotope beams. This structure information is used to inform and guide nuclear reaction modeling use to predict neutron capture reaction rate predictions off stability. You can also download a poster on his research here: 'Nuclear Science at LANSCE'.

 

Peter Kuchment, Texas A&M University
Peter Kuchment

Peter Kuchment 
Website
University Distinguished Professor
Department of Mathematics, Texas A&M University

His work is focused in the areas of mathematical physics, medical and homeland security imaging, material science, and enhancement of math education.

He had been part of a previous A&M NSF-DHS funded project devoted to prevention of smuggling illicit nuclear materials, where he with collaborators developed techniques of passive detection of presence of such sources, vs high noise background from their gamma-emission. He is currently part of a group lead by Prof. Rogachev that works on neutron detection for the same purpose of prevention of smuggling special nuclear materials.

He has written several books including 'The Radon Transform and Medical Imaging' and 'Introduction to Quantum Graphs'. You can also download few posters on his research here: 'Compton Camera Imaging' and 'Source Detection in 2D High Noise Emission Type Problems Using Cone Data'.

Shea Mosby, Los Alamos National Laboratory
Shea Mosby

Shea Mosby
Website
Research Scientist
Los Alamos National Laboratory

Neutron-induced reactions play an important role in nuclear technology and national security fields such as stockpile stewardship. Physics quantities of interest include neutron-induced fission cross sections, the fission total kinetic energy release and fission fragment mass distributions. Mosby and his team are developing an instrumentation suite which, when combined with the neutron beams available at the Los Alamos Neutron Science Center, will provide next generation experimental constraints on these quantities. Neutron-induced reactions on short-lived nuclei are an additional area of interest which pose unique challenges and preclude many of the traditional experimental techniques. His work also includes investigating both indirect probes of the reaction mechanics and the feasibility of directly studies of neutron-induced reactions in inverse kinematics. You can also download a poster on his research here: 'Nuclear Science at LANSCE'.