New astronomical observations point to a nucleosynthesis picture that goes beyond what was accepted until recently. The intermediate " i " process was proposed as a plausible scenario to explain some of the unusual abundance patterns observed in metal -poor stars. The most important nuclear physics properties entering iprocess calculations are the neutron -capture cross sections and they are almost exclusively not known experimentally. Here we provide the first experimental constraints on the 139 Ba( n, gamma ) 140 Ba reaction rate, which is the dominant source of uncertainty for the production of lanthanum, a key indicator of iprocess conditions. This is an important step towards identifying the exact astrophysical site of stars carrying the iprocess signature.

The first complete measurement of the β-decay strength distribution of _{17}^{45}Cl_{28} was performed at the Facility for Rare Isotope Beams (FRIB) with the FRIB Decay Station Initiator during the second FRIB experiment. The measurement involved the detection of neutrons and γ rays in two focal planes of the FRIB Decay Station Initiator in a single experiment for the first time. This enabled an analytical consistency in extracting the β-decay strength distribution over the large range of excitation energies, including neutron unbound states. We observe a rapid increase in the β-decay strength distribution above the neutron separation energy in _{18}^{45}Ar_{27}. This was interpreted to be caused by the transitioning of neutrons into protons excited across the Z=20 shell gap. The SDPF-MU interaction with reduced shell gap best reproduced the data. The measurement demonstrates a new approach that is sensitive to the proton shell gap in neutron rich nuclei according to SDPF-MU calculations.

Background: Type I X-Ray bursts (XRBs) are energetic stellar explosions that occur on the surface of a neutron star in an accreting binary system with a low-mass H/He-rich companion. The rate of the ^34Ar(α,p)^37K reaction may influence features of the light curve that results from the underlying thermonuclear runaway, as shown in recent XRB stellar modelling studies. Purpose: In order to reduce the uncertainty of the rate of this reaction, properties of resonances in the compound nucleus ^38Ca, such as resonance energies, spins, and particle widths, must be well constrained. Method: This work discusses a study of resonances in the ^38Ca compound nucleus produced in the ^34Ar(α,p) reaction. The experiment was performed at the National Superconducting Cyclotron Laboratory, with the ReA3 facility by measuring proton scattering using an unstable ^37K beam. The kinematics were designed specifically to identify and characterize resonances in the Gamow energy window for the temperature regime relevant to XRBs. Results: The spins and proton widths of newly identified and previously known states in ^38Ca in the energy region of interest for the ^34Ar(α,p)^37K reaction have been constrained through an R-Matrix analysis of the scattering data. Conclusions: Using these constraints, a newly estimated rate is applied to an XRB model built using Modules for Experiments in Stellar Astrophysics (MESA), to examine its impact on observables, including the light curve. It is found that the newly determined reaction rate does not substantially affect the features of the light curve.

Although most nuclei heavier than Fe are likely produced by the slow and the rapid neutron-capture ($s$ and $r$) processes, a number of medium-mass, proton-rich nuclei are thought to be produced via photo-disintegration ($\ensuremath{\gamma}$ process). To confirm this, one needs detailed statistical model calculations that are constrained by experimental input. In this work, the authors measured the ($\ensuremath{\gamma}$,$p$) reaction on the unstable ${}^{83}$Rb nucleus, via detailed balance, using the ${}^{82}$Kr($p$,$\ensuremath{\gamma}$)${}^{83}$Rb reaction with a ${}^{82}$Kr beam and detecting the produced $\ensuremath{\gamma}$ rays. The results put important constraints on the parameters of the statistical model calculations, allowing improved tests of the $\ensuremath{\gamma}$ process in hot stellar environments.

The total cross section of the $^{82}$Kr(p,$\gamma$)$^{83}$Rb reaction was measured for the first time at effective center-of-mass energies between 2.4 and 3.0 MeV, within the relevant Gamow window for the astrophysical $\gamma$ process. The experiment took place at the National Superconducting Cyclotron Laboratory at Michigan State University using the ReA facility. A $^{82}$Kr beam was directed onto a hydrogen gas cell located at the center of the Summing NaI(Tl) (SuN) detector. The obtained spectra were analyzed using the $\gamma$-summing technique and the extracted cross section was compared to standard statistical model calculations using the \textsc{non-smoker} and \textsc{talys} codes. The comparison indicates that standard statistical model calculations tend to overproduce the cross section of the $^{82}$Kr(p,$\gamma$)$^{83}$Rb reaction relative to the experimentally measured values. Furthermore, the experimental data was used to provide additional constraints on the nuclear level density and $\gamma$-ray strength function used in the statistical model calculations.

The total cross section of the 82Kr(p, gamma )83Rb reaction was measured for the first time at effective center-of -mass energies between 2.4 and 3.0 MeV, within the relevant Gamow window for the astrophysical gamma process. The experiment took place at the National Superconducting Cyclotron Laboratory at Michigan State University using the ReA facility. A 82Kr beam was directed onto a hydrogen gas cell located at the center of the Summing NaI(Tl) (SuN) detector. The obtained spectra were analyzed using the gamma-summing technique and the extracted cross section was compared to standard statistical model calculations using the NON-SMOKER and TALYS codes. The comparison indicates that standard statistical model calculations tend to overproduce the cross section of the 82Kr(p, gamma)83Rb reaction relative to the experimentally measured values. Furthermore, the experimental data were used to provide additional constraints on the nuclear level density and the gamma-ray strength function used in the statistical model calculations.

The Silicon Array for Branching Ratio Experiments (SABRE) has been developed for use to study reactions of interest to nuclear structure and astrophysics. The array has been incorporated into the Super Enge Split-Pole Spectrograph (SE-SPS) experimental setup at Florida State University's John D. Fox accelerator laboratory to detect charged-particle decays in coincidence with reaction products detected by the SE-SPS focal plane detector. Its construction and electronics processing are discussed, as well as the commissioning data used to validate its performance.