Neutron star mergers are r-process nucleosynthesis sites, which eject materials at high velocity ranging from 0.1c to 0.3c for different regions. Thus the r-process nuclei ejected from a neutron star merger event are sufficiently energetic to have spallation nuclear reactions with the interstellar medium particles. The spallation reactions tend to shift the r-process abundance patterns towards...
Understanding how the p-nuclei are created is an important step in learning more about the creation of the heavy isotopes; specifically, the isotopes on the proton-rich side of stability. Besides identifying the astrophysical sites for these events, nuclear data for all of the isotopes and their subsequent reaction rates are crucial information for simulation. Sensitivity studies have...
Though ($\alpha$,n) reaction cross sections play a key role in nuclear astrophysics and applications, many are poorly constrained by nuclear experiments and have significant uncertainties in theoretical predictions. Improving this situation will be done in part using a newly developed neutron long counter, HeBGB, at the Ohio University Edwards Accelerator Lab. The first measurement planned...
Sensitivity studies performed have indicated that $^{24}$Mg($\alpha$,p)$^{27}$Al is an important reaction in understanding the energy generation in X-ray bursts. An indirect measurement was previously made via the inverse $^{27}$Al(p,$\alpha$)$^{24}$Mg reaction; however, the measurement is limited in angular coverage. A direct measurement was also previously done via the...
The rapid neutron capture (r-process) is a nucleosynthesis process responsible for about half of the abundances of elements heavier than iron in the universe. Its astrophysical site is not uniquely identified. The observation of mass abundances in halo stars show a good agreement with the solar system r-process for Z ≥ 52 but not for the lighter elements 38 ≤ Z ≤ 47 [1]. There might be another...
In nuclear matter, bulk viscosity arises from a phase lag between an imposed density oscillation and reequilibration of the particle content of the nuclear matter, which proceeds via the Urca process. When the reequilibration proceeds at a similar rate to the density oscillation, bulk viscosity is large, causing density oscillations to be damped. We find that in neutron star mergers, in the...
The characterization of a $^{6}$Li-enhanced $(>95\%)$ CLYC detector (Cs$_{2}$LiYCl$_{6}$) at Edwards Accelerator Lab at Ohio University has begun. The $^{6}$Li enhancement increases the response to thermal neutrons while still allowing for excellent pulse-shape discrimination of $\gamma$/n events; $^{35}$Cl(n,p) events are distinguishable by Q value. Initial tests with the $^{27}$Al(d,n)...
Many astrophysically relevant ($\alpha , \gamma$) reactions on low-mass nuclei have not been well-studied within their relevant Gamow windows. These reactions are typically studied with gamma spectroscopy, which at low, astrophysically relevant energies are plagued with a poor signal-to-noise ratio. This issue can be avoided by detecting the recoil particles rather than the gamma rays using...
We present a chemical abundance analysis of the faint halo metal-poor main-sequence star J0023+0307, with [Fe/H] < ‑6.3, based on a high-resolution (R ∼ 35,000) Magellan/MIKE spectrum. The star was originally found to have [Fe/H] < ‑6.6 based on a Ca II K measurement in an R ∼ 2500 spectrum. No iron lines could be detected in our MIKE spectrum. Spectral lines of Li, C, Na, Mg, Al, Si, and Ca...
Ultra-faint dwarf galaxies are some of the oldest systems ($\sim$13Gyr) in the Milky Way halo. Studying the metallicities of their stars can place strong constraints on models of early chemical enrichment. Spectroscopy only permits the detailed chemical characterization of a handful of stars per system. This under-sampling has led to open questions such as whether the most metal-poor stars...
One-dimensional (1D) simulations of core-collapse supernovae are not able to model successful explosions. However, a lot of work has been done recently trying to incorporate multi-dimensional effects into 1D models (e.g. [1]) and building a common starting point that can be used to compare different codes [2]. In this work we compare the general relativistic Notre-Dame Livermore (NDL) code to...
The $^{15}$O($\alpha ,\gamma$)$^{19}$Ne bottleneck reaction in Type I x-ray bursts is the most important thermonuclear reaction rate to constrain experimentally, in order to improve the accuracy of burst light-curve simulations. A proposed technique to determine the thermonuclear rate of this reaction employs the $^{20}$Mg($\beta p\alpha$)$^{15}$O decay sequence. The key $^{15}$O($\alpha...
In classical novae, the $^{30}$P($p,\gamma$)$^{31}$S reaction potentially acts as a bottleneck in nucleosynthesis flow to higher masses. Knowledge of this reaction rate is necessary for the modeling of elemental and isotopic ratios in classical novae, which affect proposed nova thermometers and presolar grain identification, respectively. While most of the resonance energies are known...
The flux of neutrinos from the decays of $^{7}$Be and $^{8}$B are approximately proportional to the astrophysical S factors of $^{3}$He($\alpha$, $\gamma$)$^{7}$Be and $^{7}$Be(p, $\gamma$)$^{8}$B reactions at solar energies. Measurements of $^{3}$He+$\alpha$ and $^{7}$Be+p elastic scattering are essential for a theoretical and phenomenological understanding of these radiative capture...
We model the binary evolution of Redback and BlackWidow systems, during and after the recycling process. These are low-mass X-ray binaries that contain a neutron star (with a mass between 1:4–2:0M$_{\odot}$) and a low-mass star (with a mass of 0:5M$_{\odot}$). These systems are observed during mass transfer (Redbacks) or have already undergone a mass transfer episode (Black Widows). Using the...
Roederer et al (2016, ApJ 821, 37) suggested that the anomalous abundances of the elements with the proton number between 32 and 48 in the metal-poor ([Fe/H]=-1.6) star HD94028, in particular [As/Ge]=0.99 and [Mo/Fe]=0.97, had been produced in a weak i process. We have used a one-zone model of i-process nucleosynthesis, whose predicted elemental abundances fit the observed ones in HD94028, to...
Understanding the nucleosynthesis processes of first generation stars is key to predicting the abundances of nuclei throughout the evolution of our universe. Of particular interest in early stars are processes which can bypass the $A=5$ and $A=8$ isobars. Among these processes is the reaction sequence of $^2$H($\alpha$,$\gamma$)$^6$Li($\alpha$,$\gamma$)$^{10}$B($p$,$\alpha$)$^7$Be($\beta...
The slow neutron capture process (s-process) is a group of reactions that contribute to the production of heavy nuclides in stars. The ‘slow’ moniker refers to the fact that the neutron capture time scale is larger than the half-life of a beta-decay reaction [1]. The neutron density of the s-process is sourced by various reactions, including the ${}^{13}$C$(\alpha,n)$${}^{16}$O reaction [2,3]....
The slow neutron capture process (s-process) is a group of reactions that contribute to the production of heavy nuclides in stars. The 'slow' moniker refers to the fact that the neutron capture time scale is larger than the half-life of a beta-decay reaction [1]. The neutron density of the s-process is sourced by various reactions, including the $^{13}$C($\alpha$,n)$^{16}$O reaction [2, 3]....
The fast-expanding neutrino-driven winds in the core-collapse super-novae is a favorable scenario for the nucleosynthesis of the Z = 38-47 elements. Charge particle reactions, especially ($\alpha$,xn) on heavy nuclei of the range $80 < A < 90$ create seeds for the weak r-process populating abundances of near stable isotopes for the Sr-Cd range [1]. These abundances are significantly sensitive...
Nuclear reactions of interest for astrophysics and applications often rely on statistical model calculations to determine a nuclear reaction rate. However, the statistical properties of nuclei are often poorly constrained, particularly for cases far from beta-stability. For example, our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by...
The last abundance peak of the rapid neutron capture process, near the N = 126 shell closure, is currently the least characterized due to the difficulty in producing rare isotopes in this region. A new facility, called the N = 126 factory, is under construction at Argonne National Laboratory to produce such nuclei. A critical component of the N = 126 factory is the Notre Dame multi-reflection...
The St. George recoil mass separator at the University of Notre Dame has successfully observed its first recoils in inverse kinematics from the reaction $^{14}$N$(\alpha , \gamma)^{18}$F. The cross section of the later reaction sets the abundance for $^{22}$Ne which is a neutron source via $^{22}$Ne$(\alpha , n)^{25}$Mg for the s-process in TP-AGB, massive helium burning and carbon burning...
The rapid neutron capture process, or r-process, refers to the formation of the heavy chemical elements through the act of continuous bombardment of pre-existing atoms with neutrons. It has been theorized that neutron star mergers are the sites at which the majority of the naturally occurring lanthanides, such as Neodymium, Cerium, and Lanthanum, were made in the universe. Recently, LIGO and...
The heaviest elements in the Universe are formed as a result of the rapid neutron-capture process (r-process). The r-process-enhanced metal-poor stars found in the halo of the Milky Way likely formed in ultra-faint dwarf galaxies, their gas enriched by the early-Universe r-process. In this work, we reconstruct the orbits of a large sample (252 stars) of r-process-enhanced stars found in the...
The dependable prediction of the X-ray burst ashes require a stringent constraint on the composition of the accreted material. We calculate the alteration of accreted composition due to spallation in the atmosphere of accreting neutron stars in a full cascading destruction model. Compared to previous models with isolated destruction, the CNO element are replenished in a cascading destruction...
At the end of its life, a massive star ($>10M_{\odot}$) can collapses into a neutron star. The neutrino flux released
during the collapse is so intense that there is enough neutrino induced reaction to significantly impact the elemental nucleosynthesis. Neutrino-triggered reactions in the $\nu$-process can impact the universal abundance of $^{11}\mathrm{B}$, with the reaction...
One of the key reactions for breakout from the hot-CNO cycle into the rp-process in explosive hydrogen burning is $^{18}$Ne($\alpha$,p). At 0.4GK break-out temperature for Type-I X-ray burst conditions, capture through a 1-$\alpha$ state in $^{22}$Mg at 9.08MeV is thought to dominate the reaction rate. However, since the most reaction rate evaluation, it has been suggested that another...
At the University of Notre Dame's Nuclear Science Laboratory we have recently studied the $^{13}$C$(\alpha,n)^{16}$O reaction as a background for neutrino experiments, the $^{17}$O$(\alpha,n)^{20}$Ne reaction for its role in the $s$-process, the $^{25}$Mg$(\alpha,n)^{28}$Si reaction for its affect on $^{26}$Al nucleosynthesis, and the $^{10}$B$(\alpha,n)^{13}$N reaction as a possible...
Explosive nucleosynthesis in core collapse supernovae makes important contributions to the origin of the elements, and directly observable gamma-ray emitters such as $^{44}$Ti are ideally suited to constrain supernova models. We utilize SkyNet [1], an open source, modular reaction network, to model the isotopic abundance evolution during the explosion, and to systematically explore the impact...
Charge-exchange reactions offer a method for the testing of theoretical models for Gamow-Teller strengths that are used to calculate electron-capture rates on medium-heavy nuclei, which play important roles in astrophysical phenomena. Many of the relevant nuclei are unstable. However, a good general probe for performing charge-exchange reactions in inverse kinematics in the ($n$,$p$) reaction...
The Milky Way’s stellar halo preserves a fossil record of smaller dwarf galaxies that merged with the Milky Way throughout its formation history. Currently, though, it is difficult to reliably identify which halo stars originated in which dwarf galaxies or even which stars were definitively accreted. Selecting stars with specific chemical signatures may provide a way forward. We investigate...
Understanding of the TT neutron spectrum is necessary for accurate modeling of neutron spectra as well as for analysis of experimental data from ICF implosions. The $^5$He resonance is an important component of the TT neutron spectrum. Available OMEGA data suitable to the study of $^5$He include neutron time-of-flight spectra collected at three different ion temperatures.$^1$ These data are...
For a deeper understanding what drives nucleosynthesis in extreme astrophysical scenarios like X-Ray bursts, a variety of reaction rates of proton and alpha capture reactions with unstable isotopes have to be known but rely only on theoretical models with large uncertainties. Radioactive ion beam accelerators like at the Facility for Rare Isotope Beams (FRIB) give us great opportunities to...
We present calculations of X-ray bursts with a single-zone model to evaluate the impact of nuclear reaction rates on the model’s results. We varied individual proton and alpha capture rates in a large nuclear reaction network to asses their effect on the nucleosynthesis and the light-curve of the simulated bursts. These calculations extend the sensitivity study of Cyburt et al. to models with...
The Fisk-Vanderbilt Master’s to PhD Bridge Program was created in 2004 with the intention of increased underrepresented minorities in the STEM workforce and academe. Beginning in astronomy and physics, the program has since expanded to include biology and chemistry. To date, over 135 students have joined the program with 31 PhD graduates. With a PhD retention rate of 84%, the program has...
