The astrophysical intermediate neutron-capture process (i process) has been reinvoked in recent years to describe stellar observations that cannot be explained by the traditional nucleosynthesis processes. Despite its success, significant uncertainties still remain including the exact astrophysical conditions and site, as well as the nuclear physics input. Available i-process models strongly underproduce the abundance of strontium (Sr) compared to observational data, while successfully describing neighboring elements, like yttrium (Y) and zirconium (Zr). This discrepancy has been attributed to nuclear physics uncertainties, specifically to the unconstrained reaction rate of the neutron-capture on the isotope krypton-88. Here we present an experimental investigation of this reaction and show that our result provides a possible solution to the aforementioned Sr underproduction in i-process models. Astrophysical models underproduce the element Sr in intermediate neutron density environments (the so called i-process). The authors investigate the nuclear reactions that produce Sr and find that the new experimental reaction rates help to bridge the gap between models and observations.

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.

Background: Be-15 is an unbound nuclide that has been observed to decay by one-neutron emission. Shell model calculations predict two low-lying states in its energy spectrum; however, only a single resonance has been observed from coincident measurements of Be-14+n. It has been suggested that the yet unobserved state may decay sequentially through the first excited state in Be-14 followed by a two-neutron emission to Be-12. Purpose: The ground state of Be-15 has yet to be confirmed. A search for this predicted Be-15 state by reconstructing Be-12+3n events allows a possible determination of its ground state properties. Methods: A neutron-pickup reaction was performed with a Be-14 beam on a CD2 target (where D denotes 2H) to populate unbound Be-15 states. Decay energies were reconstructed using invariant mass spectroscopy by detecting Be-12 daughter nuclei in coincidence with up to three neutrons. Results: Evidence for at least one resonance in Be-15 is presented based on the reconstruction of Be-12+3n events. Through comparison with simulations, the energy of the strongest resonance in the analyzed reaction and decay channel is determined to be E12Be+ 3n = 330(20) keV. Conclusions: The inclusion of a new Be-15 state among the Be-12+3n events lower in relative decay energy than the previous Be-14+n observations provides the best fit to the data. Because this suggested new state would be lower in energy than the previously observed state, it is a candidate for the ground state of Be-15.

Nuclei around the N = 40 "island of inversion" exhibit interesting structure features that have been the focus of several experimental and theoretical studies. The present work presents the first complete study of the beta-decay feeding intensity distribution and Gamow-Teller distribution for the beta decay of 64Mn to 64Fe up to approximate to 10 MeV. The beta-decay intensity function was extracted from total absorption spectroscopy measurements made at the National Superconducting Cyclotron Laboratory with the Summing NaI(Tl) (SuN) detector. The experimental results are compared to shell model calculations with and without the inclusion of the nu g9/2 orbital. From this comparison it is clear that the nu g9/2 orbital is essential for the accurate description of the 64Fe beta-decay strength above approximate to 3 MeV, emphasizing once again the transitional nature of this nucleus into the N = 40 island of inversion.

Massive stars are a major source of chemical elements in the cosmos, ejecting freshly produced nuclei through winds and core-collapse supernova explosions into the interstellar medium. Among the material ejected, long-lived radioisotopes, such as 60Fe (iron) and 26Al (aluminum), offer unique signs of active nucleosynthesis in our galaxy. There is a long-standing discrepancy between the observed 60Fe/26Al ratio by γ-ray telescopes and predictions from supernova models. This discrepancy has been attributed to uncertainties in the nuclear reaction networks producing 60Fe, and one reaction in particular, the neutron-capture on 59Fe. Here we present experimental results that provide a strong constraint on this reaction. We use these results to show that the production of 60Fe in massive stars is higher than previously thought, further increasing the discrepancy between observed and predicted 60Fe/26Al ratios. The persisting discrepancy can therefore not be attributed to nuclear uncertainties, and points to issues in massive-star models.

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 i-process 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,γ)^{140}Ba reaction rate, which is the dominant source of uncertainty for the production of lanthanum, a key indicator of i-process conditions. This is an important step towards identifying the exact astrophysical site of stars carrying the i-process signature.

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 nuclear level density (NLD) is a fundamental measure of the complex structure of atomic nuclei at relatively high energies. Here we present the first model-independent measurement of the absolute partial NLD for a short-lived nucleus. For this purpose we adapt the recently introduced "shape method" for beta-decay experiments, providing the shape of the gamma-ray strength function for exotic nuclei. In this work, we show that combining the shape method with the beta-Oslo technique allows for the extraction of the NLD of the populated states without the need for theoretical input. This development opens the way for the extraction of experimental NLDs far from stability with major implications in astrophysical and other applications. We benchmark our approach using data for the stable Ge-76 nucleus, finding excellent agreement with previous experimental results. In addition, we present new experimental data and determine the absolute partial level density for the short-lived Kr-88 nucleus. Our results suggest a fivefold increase in the NLD for the case of Kr-88, compared to the recommended values from semimicroscopic Hartree-Fock Bogoliubov calculations recommended by the RIPL3 nuclear data library. However, our results are in good agreement with other semimicroscopic level density models. We demonstrate the impact of our method on the Kr-87(n,gamma) neutron capture rate and show that our experimental uncertainties for NLDs fulfill the requirements needed for astrophysical calculations predicting r-process abundances.

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.

One of the biggest questions in nuclear astrophysics is understanding where the elements come from and how they are made. This work focuses on the p process, a nucleosynthesis process that consists of a series of photodisintegration reactions responsible for producing stable isotopes on the proton-rich side of stability. These nuclei, known as the p nuclei, cannot be made through the well-known neutron-capture processes. Currently p-process models rely heavily on theory to provide the relevant reaction rates to predict the final p-nuclei abundances and more experimental data is needed. The present work reports on an experiment performed with the SuN detector at the National Superconducting Cyclotron Laboratory, NSCL, at Michigan State University using the ReA facility to measure the $^{84}$Kr(p,$\gamma$)$^{85}$Rb reaction cross section in inverse kinematics. The reverse $^{85}$Rb($\gamma$,p)$^{84}$Kr reaction is a branching point in the p-process reaction network that was highlighted as an important reaction in sensitivity studies in the production of the $^{78}$Kr p nucleus. A new hydrogen gas target was designed and fabricated and a new analysis technique for background subtraction and efficiency calculations of the detector were developed. The experimental cross section is compared to standard statistical model calculations using the NON-SMOKER and TALYS codes.

Nucleon removal reactions have been shown to be an effective tool for studying the single particle structure of nuclei. This work continues efforts to experimentally probe and benchmark the reaction and structure models used to calculate the removal reaction cross sections when using microscopic nuclear structure inputs. Three different single nucleon removal reactions were performed, from p-shell nuclei with masses A = 7, 9, and 10. The residual nuclei from the reactions were detected in coincidence with gamma rays to determine partial cross sections to individual final states. The eikonal direct-reaction model is combined with overlap functions and residual nucleus densities from microscopic, variational Monte Carlo calculations to provide consistent nuclear structure input to the partial cross section calculations. Comparisons of measured and calculated cross sections, including for mirror reactions, are presented. The analysis of the partial cross sections leading to the ground states shows a similar behavior to the one observed from analyses of inclusive cross sections using shell model nuclear structure input: the theoretical description of the removal process is in better agreement with the data when removing weakly bound nucleons, than when removing well-bound ones. The two mirror reaction pairs presented here show consistent results between the respective members of the pairs. The results obtained for the population of the excited states, however, show a systematically different trend that appears connected to the structure part of the calculation. Additional cases are needed to better understand the respective roles of structure and dynamical effects in the deviations.

This paper presents the P-decay feeding intensity distribution and Gamow-Teller transition strength distribution of Ni-71(,)73. These quantities were measured using the technique of total absorption spectroscopy at the National Superconducting Cyclotron Laboratory with the Summing NaI(T1) detector. These measurements provide sensitive constraints to theoretical models used to predict beta-decay properties far from stability for astrophysical applications. Specifically, for the astrophysical r process, the majority of the involved nuclei are not accessible by current facilities, and the nuclear input is mainly provided by theory. The present work reports on two neutron-rich nickel isotopes in the region where the weak r process is expected to be relevant in stellar nucleosynthesis. The experimental results are compared to two theoretical models, namely the shell model and the quasiparticle random-phase approximation, to help further refine theoretical calculations and aid in future r-process studies.

The $\ensuremath{\beta}$ decays of $^{103,104m}\mathrm{Nb}$ were studied with the Summing NaI(Tl) (SuN) detector at the National Superconducting Cyclotron Laboratory. The $\ensuremath{\beta}$-decay feeding intensity distribution ${I}_{\ensuremath{\beta}}(E)$ for each isotope was extracted by measuring $\ensuremath{\gamma}$ rays in coincidence with an emitted electron. The ${I}_{\ensuremath{\beta}}(E)$ was extracted via the total absorption spectroscopy technique. The ${I}_{\ensuremath{\beta}}(E)$ for each nucleus was compared to predictions made by the quasiparticle random-phase approximation (QRPA) model which is commonly used to calculate $\ensuremath{\beta}$-decay properties for astrophysical applications. The main goal was to provide experimental data for neutron-rich nuclei, relevant to the astrophysical $r$ process. In addition, the extracted $\ensuremath{\beta}$-decay feeding intensity distributions can lead to a better understanding of nuclear structure in a region of rapid structure changes around $A=100$. Finally, experimental data for $^{104m}\mathrm{Nb}$ are also of interest to antineutrino studies of nuclear reactors.

The beta decay of Zr-101,Zr-102 and Tc-109 was studied using the technique of total absorption spectroscopy. The experiment was performed at the National Superconducting Cyclotron Laboratory using the Summing NaI(Tl) (SuN) detector in the first-ever application of total absorption spectroscopy with a fast beam produced via projectile fragmentation. The beta-decay feeding intensity and Gamow-Teller transition strength distributions were extracted for these three decays. The extracted distributions were compared to three different quasiparticle random-phase approximation (QRPA) models based on different mean-field potentials. A comparison with calculations from one of the QRPA models was performed to learn about the ground-state shape of the parent nucleus. For Zr-101 and Zr-102, calculations assuming a pure shape configuration (oblate or prolate) were not able to reproduce the extracted distributions. These results may indicate that some type of mixture between oblate and prolate shapes is necessary to reproduce the extracted distributions. For Tc-109, a comparison of the extracted distributions with QRPA calculations suggests a dominant oblate configuration. The other two QRPA models are commonly used to provide beta-decay properties in r-process network calculations. This work shows the importance of making comparisons between the experimental and theoretical beta-decay distributions, rather than just half-lives and beta-delayed neutron emission probabilities, as close to the r-process path as possible.

The $\ensuremath{\beta}$ decay of $^{101,102}\mathrm{Zr}$ and $^{109}\mathrm{Tc}$ was studied using the technique of total absorption spectroscopy. The experiment was performed at the National Superconducting Cyclotron Laboratory using the Summing NaI(Tl) (SuN) detector in the first-ever application of total absorption spectroscopy with a fast beam produced via projectile fragmentation. The $\ensuremath{\beta}$-decay feeding intensity and Gamow-Teller transition strength distributions were extracted for these three decays. The extracted distributions were compared to three different quasiparticle random-phase approximation (QRPA) models based on different mean-field potentials. A comparison with calculations from one of the QRPA models was performed to learn about the ground-state shape of the parent nucleus. For $^{101}\mathrm{Zr}$ and $^{102}\mathrm{Zr}$, calculations assuming a pure shape configuration (oblate or prolate) were not able to reproduce the extracted distributions. These results may indicate that some type of mixture between oblate and prolate shapes is necessary to reproduce the extracted distributions. For $^{109}\mathrm{Tc}$, a comparison of the extracted distributions with QRPA calculations suggests a dominant oblate configuration. The other two QRPA models are commonly used to provide $\ensuremath{\beta}$-decay properties in $r$-process network calculations. This work shows the importance of making comparisons between the experimental and theoretical $\ensuremath{\beta}$-decay distributions, rather than just half-lives and $\ensuremath{\beta}$-delayed neutron emission probabilities, as close to the $r$-process path as possible.

Prussian Blue Analogues are of major interest for their use in alternative battery technologies due to their charge storing ability with a long life cycle. In this work the Prussian Blue Analogue nickel hexacyanoferrate (Ni-HCF) was produced using an all electrochemical method. Creating charge storing materials with electrochemical processes provides a new approach to the development of battery-like materials. These methods have not been commonly employed because the charge storing material yield is not directly known. The charge storage of the Ni-HCF was characterized with two different methods which provided a measure of the electrochemically active Fe present. These were then compared with the Particle Induced X-ray Emission (PIXE) method which measured the total amount of Fe present. By comparing the electrochemical measurement of active Fe to the total Fe as measured by PIXE, the percentage of material that is active in the charge storage was determined. This enables an independent calculation of the specific charge capacity of the material for comparison to other battery technologies.