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Conservation laws are deeply related to any symmetry present in a physical system1,2. Analogously to electrons in atoms exhibiting spin symmetries3, it is possible to consider neutrons and protons in the atomic nucleus as projections of a single fermion with an isobaric spin (isospin) of t = 1/2 (ref. 4). Every nuclear state is thus characterized by a total isobaric spin T and a projection Tz—two quantities that are largely conserved in nuclear reactions and decays5,6. A mirror symmetry emerges from this isobaric-spin formalism: nuclei with exchanged numbers of neutrons and protons, known as mirror nuclei, should have an identical set of states7, including their ground state, labelled by their total angular momentum J and parity π. Here we report evidence of mirror-symmetry violation in bound nuclear ground states within the mirror partners strontium-73 and bromine-73. We find that a J π = 5/2− spin assignment is needed to explain the proton-emission pattern observed from the T = 3/2 isobaric-analogue state in rubidium-73, which is identical to the ground state of strontium-73. Therefore the ground state of strontium-73 must differ from its J π = 1/2− mirror bromine-73. This observation offers insights into charge-symmetry-breaking forces acting in atomic nuclei. Observations of the decay of 73Sr, when compared to its mirror nucleus 73Br, indicate that the spin assignment of their ground states differ, demonstrating mirror-symmetry violation.

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 $\ensuremath{\beta}$ 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.

The interpretation of observations of cooling neutron star crusts in quasipersistent x-ray transients is affected by predictions of the strength of neutrino cooling via crust Urca processes. The strength of crust Urca neutrino cooling depends sensitively on the electron-capture and $\ensuremath{\beta}$-decay ground-state-to-ground-state transition strengths of neutron-rich rare isotopes. Nuclei with a mass number of $A=61$ are predicted to be among the most abundant in accreted crusts, and the last remaining experimentally undetermined ground-state-to-ground-state transition strength was the $\ensuremath{\beta}$ decay of $^{61}\mathrm{V}$. This Letter reports the first experimental determination of this transition strength, a ground-state branching of ${8.1}_{\ensuremath{-}3.1}^{+4.0}%$, corresponding to a log $ft$ value of ${5.5}_{\ensuremath{-}0.2}^{+0.2}$. This result was achieved through the measurement of the $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays using the total absorption spectrometer SuN and the measurement of the $\ensuremath{\beta}$-delayed neutron branch using the neutron long counter system NERO at the National Superconducting Cyclotron Laboratory at Michigan State University. This method helps to mitigate the impact of the pandemonium effect in extremely neutron-rich nuclei on experimental results. The result implies that $A=61$ nuclei do not provide the strongest cooling in accreted neutron star crusts as expected by some predictions, but that their cooling is still larger compared to most other mass numbers. Only nuclei with mass numbers 31, 33, and 55 are predicted to be cooling more strongly. However, the theoretical predictions for the transition strengths of these nuclei are not consistently accurate enough to draw conclusions on crust cooling. With the experimental approach developed in this work, all relevant transitions are within reach to be studied in the future.

This paper reports on the first β-decay study of 74,75Cu isotopes using the technique of total absorption spectroscopy (TAS). The experiment was performed at the National Superconducting Cyclotron Laboratory at Michigan State University using the Summing NaI(Tl) (SuN) detector. The Cu isotopes are good candidates to probe the single-particle structure in the region because they have one proton outside the Z = 28 shell. Comparing the β-decay intensity distributions in the daughter Zn isotopes to the theoretical predictions provides a stringent test of the calculations. The nuclei in this region are also identified as playing an important role in the astrophysical r-process. The measured β-decay intensity distributions provide essential nuclear physics inputs required to better understand heavy element nucleosynthesis.

Spin–isospin excitations in Nb 100 were studied via the Mo 100 ( t , He 3 ) charge-exchange reaction at 115 MeV/u with the goal to constrain theoretical models used to describe the isovector spin response of nuclei. The experiment was performed with a secondary beam of tritons, and 3He particles were analyzed in the S800 magnetic spectrometer. Decay by neutron emission from excited states in Nb 100 was observed by using plastic and liquid scintillator arrays. Differential cross sections were analyzed and monopole excitations were revealed by using a multipole decomposition analysis. The Gamow–Teller transition strength observed at low excitation energies, which is important for estimating the electron-capture rate in astrophysical scenarios, was strongly fragmented and reduced compared to single-particle and spherical mean-field models. The consideration of deformation in the theoretical estimates was found to be important to better describe the fragmentation and strengths. A strong excitation of the isovector spin giant monopole resonance was observed, and well reproduced by the mean-field models. Its presence makes the extraction of Gamow–Teller strengths at high excitation energies difficult. The branches for statistical and direct decay by neutron emission were identified in the spectra. The upper limit for the branching ratio by direct decay (integrated over all observed excitations) was determined to be 20 ± 6 % . Even though the statistical uncertainties in the neutron-coincident data were too large to perform detailed studies of the decay by neutron emission from individual states and resonances, the experiment demonstrates the feasibility of the method.

Background: The rapid neutron capture process is one of the main nucleosynthesis processes of elements heavier than Fe. Uncertainties in nuclear properties, such as masses, half-lives, and $\ensuremath{\beta}$-delayed neutron probabilities can cause orders of magnitude of variation within astrophysical $r$-process simulations. Presently, theoretical models are used to make global predictions of various nuclear properties for the thousands of nuclei required for these simulations, and measurements are required to benchmark these models, especially far from stability.Purpose: $\ensuremath{\beta}$-decay strength distributions can be used to not only inform astrophysical $r$-process simulations, but also to provide a stringent test for theoretical calculations. The aim of this work is to provide accurate strength distributions for $^{69,71}\mathrm{Co}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay.Method: The technique of total absorption spectroscopy was used to measure the $\ensuremath{\beta}$ decay of $^{69,71}\mathrm{Co}$ for the first time at the National Superconducting Cyclotron Laboratory. The ions were implanted in a double-sided silicon strip detector at the center of the Summing NaI(Tl) detector and identified using standard particle identification methods. The response of the detection system to the $\ensuremath{\beta}$-decay electron and subsequent $\ensuremath{\gamma}$-ray radiation was fit to the observed experimental data using a ${\ensuremath{\chi}}^{2}$-minimization technique.Results: $\ensuremath{\beta}$-feeding intensities and Gamow-Teller strength distributions were extracted from the fits of the experimental data. The $\ensuremath{\beta}$-decay intensities show that there is a large percentage of feeding to levels above 2 MeV, which have not been observed in previous studies. The resultant $\ensuremath{\beta}$-feeding intensities and Gamow-Teller strength distributions were compared to shell model and quasiparticle random phase approximation (QRPA) calculations.Conclusions: Comparing experimentally determined $\ensuremath{\beta}$-decay strength distributions provides a test of models, which are commonly used for global $\ensuremath{\beta}$-decay properties for astrophysical calculations. This work highlights the importance of performing detailed comparisons of models to experimental data, particularly far from stability and as close to the $r$-process path as possible.

Proper understanding of the stellar nucleosynthesis processes requires information on a variety of capture reaction cross sections. Since these cross sections are typically very low, they require efficient measurement techniques. The High Efficiency Total Absorption Spectrometer (HECTOR) was designed to measure capture cross sections relevant for astrophysical processes. HECTOR is a $ \gamma$ -summing detector comprised of 16 separate NaI(Tl) segments. The detector design is presented, as well as a detailed study of the detector's summing efficiency and analysis procedure. The results of the commissioning of HECTOR are presented. The resonance strengths of the well-known resonances in the 27Al $ (\mathrm{p},\gamma)$28Si reaction measured with HECTOR are compared with the literature values.

This corrects the article DOI: 10.1103/PhysRevLett.116.242502.

Background: The recent observation of a neutron-star merger finally confirmed one astrophysical location of the rapid neutron-capture process (r-process). Evidence of the production of $Al140$ nuclei was seen, but there is still little detailed information about how those lighter elements are produced in such an environment. Many of the questions surrounding the $A\ensuremath{\approx}80$ nuclei are likely to be answered only when the nuclear physics involved in the production of r-process nuclei is well understood. Neutron-capture reactions are an important component of the r-process, and neutron-capture cross sections of r-process nuclei, which are very neutron rich, have large uncertainties.Purpose: Indirectly determine the neutron-capture cross section and reaction rate of $^{73}\mathrm{Zn}(n,\ensuremath{\gamma})^{74}\mathrm{Zn}$.Methods: The nuclear level density (NLD) and $\ensuremath{\gamma}$-ray strength function ($\ensuremath{\gamma}\mathrm{SF}$) of $^{74}\mathrm{Zn}$ were determined following a total absorption spectroscopy (TAS) experiment focused on the $\ensuremath{\beta}$ decay of $^{74}\mathrm{Cu}$ into $^{74}\mathrm{Zn}$ performed at the National Superconducting Cyclotron Laboratory. The NLD and $\ensuremath{\gamma}\mathrm{SF}$ were used as inputs in a Hauser-Feshbach statistical model to calculate the neutron-capture cross section and reaction rate.Results: The NLD and $\ensuremath{\gamma}\mathrm{SF}$ of $^{74}\mathrm{Zn}$ were experimentally constrained for the first time using $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays measured with TAS and the $\ensuremath{\beta}$-Oslo method. The NLD and $\ensuremath{\gamma}\mathrm{SF}$ were then used to constrain the neutron-capture cross section and reaction rate for the $^{73}\mathrm{Zn}(n,\ensuremath{\gamma})^{74}\mathrm{Zn}$ reaction.Conclusions: The uncertainty in the neutron-capture cross section and reaction rate of $^{73}\mathrm{Zn}(n,\ensuremath{\gamma})^{74}\mathrm{Zn}$ calculated in TALYS was reduced to under a factor of 2 from a factor of 5 in the cross section and a factor of 11 in the reaction rate using the experimentally obtained NLD and $\ensuremath{\gamma}\mathrm{SF}$.

$\ensuremath{\beta}$-decay half-lives of neutron-rich nuclides in the $A=100--110$ mass region have been measured using an implantation station installed inside of the Summing NaI(Tl) (SuN) detector at the National Superconducting Cyclotron Laboratory. Accurate half-lives for these nuclides are important for nuclear astrophysics, nuclear structure, and nuclear technology. The half-lives from the present work are compared with previous measurements, showing overall good agreement.

Numerous scientific fields including astrophysics, nuclear power, and nuclear forensics require a knowledge of basic nuclear properties for large numbers of short-lived, radioactive isotopes far removed from stable nuclei. Neutron-capture cross sections are one such piece of nuclear data where direct measurements are not possible and theoretical predictions can vary by orders of magnitude. A recently developed indirect technique for inferring neutron capture rates, the β -Oslo method, has been introduced but not compared against a known, directly measured neutron capture cross section. To provide this benchmark, two indirect methods based on β decay and charged-particle reactions were used to extract the nuclear level density and γ -ray strength function of 51 Ti . The nuclear level density and γ -ray strength function from the two data sets were found to be equivalent and were used to extract the neutron capture cross section of 50 Ti which agrees with previous direct measurements at high neutron energies. The results demonstrate the validity of the β -Oslo method for extracting neutron capture cross sections of short-lived nuclei and provide a sufficiently small uncertainty to be used in various applications.

The nucleosynthesis path of the γ-process is predominantly governed by the branching points at which the flow of the initial (γ,n) is redirected by either (γ,p) or (γ,α) reactions. In this work, the inverse reactions, proton and α capture on 108Cd were studied in order to aid in verification of the 112Sn isotope as a potential branching point in the γ-process. The results of the first measurement with a γ-summing detector, HECTOR, are compared with previous measurements found in the literature and with NON-SMOKER predictions. The results of this work will provide input for Hauser-Feshbach calculations to obtain the γ induced reaction rates.

Neutron-capture reactions on very neutron-rich nuclei are essential for heavy-element nucleosynthesis through the rapid neutron-capture process, now shown to take place in neutron-star merger events. For these exotic nuclei, radiative neutron capture is extremely sensitive to their $\ensuremath{\gamma}$-emission probability at very low $\ensuremath{\gamma}$ energies. In this work, we present measurements of the $\ensuremath{\gamma}\text{-decay}$ strength of $^{70}\mathrm{Ni}$ over the wide range $1.3\ensuremath{\le}{E}_{\ensuremath{\gamma}}\ensuremath{\le}8$ MeV. A significant enhancement is found in the $\ensuremath{\gamma}\text{-decay}$ strength for transitions with ${E}_{\ensuremath{\gamma}}l3$ MeV. At present, this is the most neutron-rich nucleus displaying this feature, proving that this phenomenon is not restricted to stable nuclei. We have performed $E1$-strength calculations within the quasiparticle time-blocking approximation, which describe our data above ${E}_{\ensuremath{\gamma}}\ensuremath{\simeq}5$ MeV very well. Moreover, large-scale shell-model calculations indicate an $M1$ nature of the low-energy $\ensuremath{\gamma}$ strength. This turns out to be remarkably robust with respect to the choice of interaction, truncation, and model space, and we predict its presence in the whole isotopic chain, in particular the neutron-rich $^{72,74,76}\mathrm{Ni}$.

The Summing NaI(Tl) detector (SuN) is used in nuclear astrophysics experiments measuring (p,γ) and (α,γ) reactions. The main background in these experiments in the energy region of interest comes from cosmic rays. The Scintillating Cosmic Ray Eliminating Ensemble (SuNSCREEN) was developed to be combined with the SuN detector to increase the sensitivity of reaction cross-section measurements by reducing the cosmic-ray background. SuNSCREEN is a plastic scintillating array consisting of 9 bars, which are positioned in a roof-like configuration above SuN. A significant reduction of the background was observed in the energy region of interest.

In this contribution we discuss new experimental approaches to indirectly provide information on neutron-capture rates relevant to the $r$-process. In particular, we focus on applications of the Oslo method to extract fundamental nuclear properties for reaction-rate calculations: the nuclear level density and the $\gamma$ strength function. Two methods are discussed in detail, the Oslo method in inverse kinematics and the beta-Oslo method. These methods present a first step towards constraining neutron-capture rates of importance to the $r$-process.

Neutron-capture reactions play an important role in heavy element nucleosynthesis, since they are the driving force for the two processes that create the vast majority of the heavy elements. When a neutron capture occurs on a short-lived nucleus, it is extremely challenging to study the reaction directly and therefore the use of indirect techniques is essential. The present work reports on such an indirect measurement that provides strong constraints on the 68Ni(n, γ)69Ni reaction rate. This is done by populating the compound nucleus 69Ni via the β decay of 69Co and measuring the γ-ray deexcitation of excited states in 69Ni. The β-Oslo method was used to extract the γ-ray strength function and the nuclear level density. In addition the half-life of 69Co was extracted and found to be in agreement with previous literature values. Before the present results, the 68Ni(n, γ)69Ni reaction was unconstrained and the purely theoretical reaction rate was highly uncertain. The new uncertainty on the reaction rate based on the present experiment (variation between upper and lower limit) is approximately a factor of 3. The commonly used reaction libraries JINA-REACLIB and BRUSLIB are in relatively good agreement with the experimental rate. The impact of the new rate on weak r-process calculations is discussed. This research was first published in Journal of Physics G: Nuclear and Particle Physics. © IOP Publishing.

The γ - summing technique was successfully implemented for the first time in inverse kinematics using the NSCL Summing NaI(Tl) detector at the Nuclear Science Laboratory of the University of Notre Dame. This new method offers a way to measure (p,γ) and (α,γ) reactions on unstable nuclei, which are critical for an improved understanding of nucleosynthesis. As a proof of principle, the well-known resonances at E c . m . = 956 keV in the p(27Al,γ)28Si reaction and at E c . m . = 1400 keV in the p(58Ni,γ)59Cu reaction were measured and their resonance strengths were deduced. The values of the present work agree well with the reported literature values, demonstrating the viability of the technique.

The $\ensuremath{\beta}$-decay intensity of $^{70}\mathrm{Co}$ was measured for the first time using the technique of total absorption spectroscopy. The large $\ensuremath{\beta}$-decay $Q$ value [12.3(3) MeV] offers a rare opportunity to study $\ensuremath{\beta}$-decay properties in a broad energy range. Two surprising features were observed in the experimental results, namely, the large fragmentation of the $\ensuremath{\beta}$ intensity at high energies, as well as the strong competition between $\ensuremath{\gamma}$ rays and neutrons, up to more than 2 MeV above the neutron-separation energy. The data are compared to two theoretical calculations: the shell model and the quasiparticle random phase approximation (QRPA). Both models seem to be missing a significant strength at high excitation energies. Possible interpretations of this discrepancy are discussed. The shell model is used for a detailed nuclear structure interpretation and helps to explain the observed $\ensuremath{\gamma}$-neutron competition. The comparison to the QRPA calculations is done as a means to test a model that provides global $\ensuremath{\beta}$-decay properties for astrophysical calculations. Our work demonstrates the importance of performing detailed comparisons to experimental results, beyond the simple half-life comparisons. A realistic and robust description of the $\ensuremath{\beta}$-decay intensity is crucial for our understanding of nuclear structure as well as of $r$-process nucleosynthesis.

The $\ensuremath{\beta}$ decay of $^{76}\mathrm{Ga}$ was studied using the technique of total absorption spectroscopy for the first time. The experiment was performed at the National Superconducting Cyclotron Laboratory using the Summing NaI(Tl) detector. The extracted $\ensuremath{\beta}$-decay feeding intensity distribution and Gamow-Teller transition strength distribution are compared to shell-model calculations to help constrain nuclear matrix elements relevant to the neutrinoless double-$\ensuremath{\beta}$ decay of $^{76}\mathrm{Ge}$.

Nuclear reactions where an exotic nucleus captures a neutron are critical for a wide variety of applications, from energy production and national security, to astrophysical processes, and nucleosynthesis. Neutron capture rates are well constrained near stable isotopes where experimental data are available; however, moving far from the valley of stability, uncertainties grow by orders of magnitude. This is due to the complete lack of experimental constraints, as the direct measurement of a neutron-capture reaction on a short-lived nucleus is extremely challenging. Here, we report on the first experimental extraction of a neutron capture reaction rate on ^{69}Ni, a nucleus that is five neutrons away from the last stable isotope of Ni. The implications of this measurement on nucleosynthesis around mass 70 are discussed, and the impact of similar future measurements on the understanding of the origin of the heavy elements in the cosmos is presented.

Author(s): Crider, BP; Prokop, CJ; Liddick, SN; Al-Shudifat, M; Ayangeakaa, AD; Carpenter, MP; Carroll, JJ; Chen, J; Chiara, CJ; David, HM; Dombos, AC; Go, S; Grzywacz, R; Harker, J; Janssens, RVF; Larson, N; Lauritsen, T; Lewis, R; Quinn, SJ; Recchia, F; Spyrou, A; Suchyta, S; Walters, WB; Zhu, S | Abstract: Shape coexistence near closed-shell nuclei, whereby states associated with deformed shapes appear at relatively low excitation energy alongside spherical ones, is indicative of the rapid change in structure that can occur with the addition or removal of a few protons or neutrons. Near 68Ni (Z=28, N=40), the identification of shape coexistence hinges on hitherto undetermined transition rates to and from low-energy 0+ states. In 68,70Ni, new lifetimes and branching ratios have been measured. These data enable quantitative descriptions of the 0+ states through the deduced transition rates and serve as sensitive probes for characterizing their nuclear wave functions. The results are compared to, and consistent with, large-scale shell-model calculations which predict shape coexistence. With the firm identification of this phenomenon near 68Ni, shape coexistence is now observed in all currently accessible regions of the nuclear chart with closed proton shells and mid-shell neutrons.

In recent models, the neutron-rich Ni isotopes around $N=40$ are predicted to exhibit multiple low-energy excited ${0}^{+}$ states attributed to neutron and proton excitations across both the $N=40$ and $Z=28$ shell gaps. In $^{68}\mathrm{Ni}$, the three observed ${0}^{+}$ states have been interpreted in terms of triple shape coexistence between spherical, oblate, and prolate deformed shapes. In the present work a new $({0}_{2}^{+})$ state at an energy of 1567 keV has been discovered in $^{70}\mathrm{Ni}$ by using $\ensuremath{\beta}$-delayed, $\ensuremath{\gamma}$-ray spectroscopy following the decay of $^{70}\mathrm{Co}$. The precipitous drop in the energy of the prolate-deformed ${0}^{+}$ level between $^{68}\mathrm{Ni}$ and $^{70}\mathrm{Ni}$ with the addition of two neutrons compares favorably with results of Monte Carlo shell-model calculations carried out in the large $fp{g}_{9/2}{d}_{5/2}$ model space, which predict a ${0}_{2}^{+}$ state at 1525 keV in $^{70}\mathrm{Ni}$. The result extends the shape-coexistence picture in the region to $^{70}\mathrm{Ni}$ and confirms the importance of the role of the tensor component of the monopole interaction in describing the structure of neutron-rich nuclei.

The $^{90}\mathrm{Zr}(\ensuremath{\alpha},\ensuremath{\gamma})^{94}\mathrm{Mo},\phantom{\rule{0.16em}{0ex}}^{92}\mathrm{Zr}(\ensuremath{\alpha},\ensuremath{\gamma})^{96}\mathrm{Mo}$, and $^{74}\mathrm{Ge}(\ensuremath{\alpha},\ensuremath{\gamma})^{78}\mathrm{Se}$ reaction cross sections were measured for the first time in an effort to expand the existing experimental database for $(\ensuremath{\alpha},\ensuremath{\gamma})$ reactions relevant for the production of $p$ nuclei in the universe. In particular, the $^{90}\mathrm{Zr}(\ensuremath{\alpha},\ensuremath{\gamma})^{94}\mathrm{Mo}$ reaction was identified by a sensitivity study for its potential impact on the $\ensuremath{\gamma}$-process mass flow in the region of light $p$ nuclei. The measurements were performed for energies ${E}_{\ensuremath{\alpha}}=9.5--12.0$ MeV at the University of Notre Dame using the SuN detector and the $\ensuremath{\gamma}$-summing technique. The results are compared to theoretical calculations from the talys and non-smoker nuclear reaction codes, and it is shown that the data greatly reduce the uncertainty in the cross section for the measured energies. The talys parameters that provide the best description of the experimental data are reported.

A systematic measurement of the $(\ensuremath{\alpha},\ensuremath{\gamma})$ reaction for all the stable nickel isotopes has been performed using the $\ensuremath{\gamma}$-summing technique. For two of the isotopes, $^{60}\mathrm{Ni}$ and $^{61}\mathrm{Ni}$, the $\ensuremath{\alpha}$-capture cross sections have been experimentally measured for the first time. For $^{58,62,64}\mathrm{Ni}$, the current measurement is in excellent agreement with earlier results found in the literature, and additionally extends the energy range of the measured cross sections up to 8.7 MeV. The data provided a tool for testing the cross section predictions of Hauser-Feshbach calculations. The experimental results were compared to the cross sections calculated with the talys 1.6 code and commonly used databases non-smoker and bruslib. For each of the investigated isotopes a combination of input parameter for talys was identified that best reproduces the experimental data, and recommended reaction rate has been calculated. Additionally, a set of inputs for Hauser-Feshbach calculations was given that, simultaneously for all the isotopes under consideration, reproduces the experimental data within the experimental uncertainties.

This paper reports on the first cross section measurement of the $^{72}\mathrm{Ge}(p,\ensuremath{\gamma})^{73}\mathrm{As}$ reaction. The proton capture reaction on $^{72}\mathrm{Ge}$ is relevant to the astrophysical $p$-process and was identified in a sensitivity study as one of the important reactions required to estimate the abundances of the light $p$ nuclei. The $\ensuremath{\gamma}$-summing technique was employed using the summing NaI(Tl) detector (SuN) from the National Superconducting Cyclotron Laboratory. The experiment was performed at the University of Notre Dame using a 1.8--3.6 MeV proton beam. In order to test the predictive power of different theoretical calculations in the region, experimental values were compared to the results given by the nuclear reaction code talys1.6. The theoretical uncertainties in the cross section arising from different combinations of nuclear level densities, $\ensuremath{\gamma}$-ray strength functions, and optical model potentials were reduced to 10--18% by the experimental data. The recommended reaction rates from the standard astrophysical libraries, BRUSLIB and REACLIB, are found to be in good agreement with the experimental results.

A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the $r$ process. As a proof of principle, the $\ensuremath{\gamma}$ spectra from the $\ensuremath{\beta}$ decay of $^{76}\mathrm{Ga}$ have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and $\ensuremath{\gamma}$-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the $^{75}\mathrm{Ge}(n,\ensuremath{\gamma})^{76}\mathrm{Ge}$ cross section and reaction rate.

Funding Details: PHY 08-22648, NSF, National Science Foundation; PHY 0969058, NSF, National Science Foundation; PHY 1102511, NSF, National Science Foundation

Cross section measurements of the reactions ${}^{90,92}$Zr($p$,$\ensuremath{\gamma}$)${}^{91,93}$Nb were performed using the National Superconducting Cyclotron Laboratory Summing NaI(Tl) detector at the University of Notre Dame. These reactions are part of the nuclear reaction flow for the synthesis of the light $p$ nuclei. For the ${}^{90}$Zr($p$,$\ensuremath{\gamma}$)${}^{91}$Nb reaction the new measurement resolves the disagreement between previous results. For the ${}^{92}$Zr($p$,$\ensuremath{\gamma}$)${}^{93}$Nb reaction the present work reports the first measurement of this reaction cross section. Both reaction cross sections are compared to theoretical calculations and a very good agreement with the standard non-smoker model is observed.

In an effort to investigate the production of ${}^{74}$Se in $p$-process nucleosynthesis, the ${}^{74}$Ge($p$,$\ensuremath{\gamma}$)${}^{75}$As reaction cross section was measured in the relevant energy range of ${E}_{p}=1.6$--4.2 MeV. The measurements were carried out using the NSCL SuN detector at the University of Notre Dame. The results are in good agreement with previous work, extending the measurements to both lower and higher energies. The measurements are compared to theoretical predictions using the non-smoker and talys nuclear reaction codes. New and improved reaction rates are offered, and these reaction rates are used in a 25M${}_{\ensuremath{\bigodot}}$ Type II Supernova model to study their impact on the production of ${}^{74}$Se.