Ryan Amberger ’23, a Ph.D. candidate in the Department of Physics and Astronomy at Texas A&M University, has been selected to receive a 2025 Los Alamos National Laboratory-Texas A&M University System Graduate Fellowship in recognition of his graduate research and potential to address central challenges in nuclear science.
The $75,000 fellowship, jointly sponsored by the Texas A&M University System and Los Alamos National Laboratory, provides up to a year of support for Ph.D. candidates seeking to conduct dissertation research with Los Alamos, including in-residency time at the laboratory. Proposal-based applications are evaluated by a team of subject-matter experts from Los Alamos and the Texas A&M System and ranked on the basis of qualifications and academic preparation, technical merit, and strength of mentorship, training and potential for long-term partnership. In addition to a stipend, the award covers educational expenses, travel and related research materials.
Amberger is a third-year graduate student in Dr. Philip Adsley’s research group within Texas A&M’s Cyclotron Institute. Adsley, a physicist, is the recipient of the 2023 Department of Energy Early Career Research Award. Since June 2022, Amberger has contributed as a graduate research assistant. Together, he and Adsley study nuclear astrophysics, a branch of nuclear physics focused on the nuclear reactions occurring inside of stars. Amberger’s particular focus is on the s-process, or slow process, which is how half of the elements in the universe heavier than iron are made.
Processing The Unknowns
Fusion reactions in stars between helium and two isotopes, carbon-13 and neon-22, produce neutrons. During the s-process, Amberger explains, these excess neutrons are captured by nuclei inside of stars. The nuclei then undergo another process called beta decay in which a neutron changes into an electron and proton. The electron is ejected from the nucleus, while the proton remains, effectively changing the nucleus into a new element with a proton number one higher than the original element. The s-process can then repeat, allowing for successively heavier elements to be made.
“Two important unknowns for this process are, one, how many neutrons are available? and two, what is the likelihood of neutrons colliding with nuclei, also known as neutron cross section?” Amberger explained. “My work with Phil is trying to improve our understanding of the first problem.”
When it comes to nuclear science, particularly nuclear chemistry, all processes and problems tie back to the Periodic Table, in which each element has an atomic number indicating the number of protons present in every atom of that element. However, atoms of the same element can differ in their number of neutrons, resulting in isotopes that are then classified according to their different mass numbers — an integer which is based on the total number of protons and neutrons present in the isotope.
Amberger and Adsley have narrowed down their search to two specific reactions, both of which involve isotopes of neon (Ne-22) and magnesium (Mg-26) and an alpha particle. However, each reaction results in differing outputs. One produces a neutron, while the other produces a gamma ray — a result that Amberger says is caused by their decay rate. He is studying a third reaction — more specifically, its byproducts — In order to better understand that decay rate.
“Understanding how likely Mg-26 is to decay by either a neutron or a gamma ray, also known as the branching ratio, will help us understand how many neutrons are available,” Amberger added.
Targeting Neutron Capture
Amberger intends to tackle the second unknown within the s-process in collaboration with researchers at the Los Alamos Neutron Science Center, which is home to one of the nation’s most powerful linear accelerators (LINAC) as well as a highly sophisticated instrument known as DICER (Device for Indirect Capture Experiments on Radionuclides). His proposal, entitled “Neutron-induced reactions; neutrons for s-process,” outlines the use of DICER to develop a better understanding of neutron cross sections, or the likelihood of neutrons being captured by target nuclei during experiments. Amberger will be in residence at Los Alamos from April 2025 through March 2026, working with DICER under the mentorship of Thanos Stamatopoulos, a DICER instrument scientist and nuclear physicist at Los Alamos.
“DICER works by firing a beam of neutrons of various energies at a target material that we want to measure the neutron-capture cross section of,” Amberger said. “Behind the target is a neutron detector that counts all the neutrons not captured by the target. By comparing how many neutrons at a given energy are seen in the detector to how many neutrons of that energy were fired at the target, we can learn how many neutrons were captured in the target, which will tell us the neutron cross section.”
A native of Benbrook, Texas, Amberger earned his bachelor of science in math and physics at the University of Texas at Arlington prior to beginning his Ph.D. in physics at Texas A&M in fall 2021 with Adsley as his advisor.
Ryan is a talented experimental physicist, designing and building equipment for the laboratory, utilizing different detector systems and even making his own targets for experiments. Working at LANL will give him an even broader experience of experimental techniques, including those which are not available at the Cyclotron Institute, such as neutron scattering.
“Nuclear science means that one needs to be familiar with many different experimental techniques,” Adsley said. “Ryan is a talented experimental physicist, designing and building equipment for the laboratory, utilizing different detector systems and even making his own targets for experiments. Working at LANL will give him an even broader experience of experimental techniques, including those which are not available at the Cyclotron Institute, such as neutron scattering.
“The new techniques he will learn have wide application in nuclear safety, national security and the production of isotopes for medical purposes, in addition to the astrophysical implications. We are grateful that he has this opportunity and hope he will be able to use it as a pathway into a career in nuclear science.”
Los Alamos National Laboratory is a multidisciplinary research institution engaged in strategic science on behalf of national security. It is managed by Triad, a public service oriented, national security science organization equally owned by its three founding members: Battelle Memorial Institute, the Texas A&M University System and the Regents of the University of California for the Department of Energy’s National Nuclear Security Administration.