Search

Due to its importance as an astronomical observable in core-collapse supernovae (CCSNe), the reactions producing and destroying $^{44}\mathrm{Ti}$ must be well constrained. Generally, statistical model calculations such as Hauser-Feshbach are employed when experimental cross sections are not available, but the variation in such adopted rates can be large. Here, data from the literature is compared with statistical model calculations of the $^{44}\mathrm{Ti}(\ensuremath{\alpha},p)^{47}\mathrm{V}$ reaction cross section and used to constrain the possible reaction rate variation over the temperatures relevant to CCSNe. Suggestions for targeted future measurements are given.

Precise antineutrino measurements are very sensitive to proper background characterization. We present an improved measurement of the $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$ reaction cross section which constitutes significant background for large $\overline{\ensuremath{\nu}}$ detectors. We greatly improve the precision and accuracy by utilizing a setup that is sensitive to the neutron energies while making measurements of the excited state transitions via secondary $\ensuremath{\gamma}$-ray detection. Our results shows a 54% reduction in the background contributions from the $^{16}\mathrm{O}({3}^{\ensuremath{-}},6.13\text{ }\mathrm{MeV})$ state used in the KamLAND analysis.

The $^{7}\mathrm{Li}(\ensuremath{\gamma},t)^{4}\mathrm{He}$ ground state cross section was measured for the first time using monoenergetic $\ensuremath{\gamma}$ rays with energies between 4.4 and 10 MeV at the High Intensity Gamma-ray Source. The reaction is important for the primordial Li problem and for testing our understanding of the mirror $\ensuremath{\alpha}$-capture reactions $^{3}\mathrm{H}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Li}$ and $^{3}\mathrm{He}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Be}$. Although over the last 30 years most measurements of the $^{3}\mathrm{H}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Li}$ reaction have concentrated in an energy range below ${E}_{\ensuremath{\gamma}}=3.65$ MeV, measurements at higher energies could potentially restrict the extrapolation to astrophysically important energies. The experimental arrangement for measuring the $^{7}\mathrm{Li}(\ensuremath{\gamma},t)^{4}\mathrm{He}$ reaction included a large-area silicon detector array and several beam characterization instruments. The experimental astrophysical $S$ factor of $^{3}\mathrm{H}(\ensuremath{\alpha},\ensuremath{\gamma})$ calculated from the present data was fitted using the $R$-matrix formalism. The results are in disagreement with previous experimental measurements in the same energy range but the extrapolated $S$ factor agrees with the potential model calculation and lower energy experimental data.

The $$^{22}\hbox {Na}(p,\gamma )^{23}\hbox {Mg}$$ reaction is responsible for destruction of the long-lived radionuclide $$^{22}\hbox {Na}$$ produced during nova explosions. Since the reaction proceeds through resonances from levels in $$^{23}\hbox {Mg}$$ above the proton threshold at 7.581 MeV, the properties of these levels such as excitation energies, spins, and parities are crucial ingredients to determine the $$^{22}\hbox {Na}(p,\gamma )^{23}\hbox {Mg}$$ reaction rate. Despite recent studies of these levels, their spins are not well constrained in many cases. We have measured the $$^{24}\mathrm{Mg}(p,d)^{23}\hbox {Mg}$$ transfer reaction to determine spectroscopic properties of these levels at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spin of the $$E_{x}$$ = 7.788 MeV level in $$^{23}\hbox {Mg}$$ is constrained to be $$J^{\pi }$$ = (3/2$$^+$$, 5/2$$^+$$) through the present work. The astrophysical $$^{22}\hbox {Na}(p,\gamma )^{23}\hbox {Mg}$$ reaction rate at nova temperatures is updated accordingly. Nova nucleosynthesis model calculations using the newly updated $$^{22}\hbox {Na}(p,\gamma )^{23}\hbox {Mg}$$ reaction rate shows that the final weighted abundance of the radionuclide $$^{22}\hbox {Na}$$ is increased by 42% compared to that obtained by using the previous $$^{22}\hbox {Na}(p,\gamma )^{23}\hbox {Mg}$$ reaction rate of Sallaska et al. for a 1.35 $$M_{\odot }$$ ONeMg white dwarf.

In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron orbits of 132Sn. The spectroscopic strength of single-hole states in 131Sn was determined from the measured differential cross sections of the tritons from the neutron-removing 132Sn(d, t)131Sn reaction, which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spectroscopic factors of the lowest 3/2+, 1/2+ and 5/2+ states were found to be consistent with their maximal values of (2j+1), confirming the robust N=82 shell closure at 132Sn. We compared the spin-orbit splitting of neutron single-hole states in 131Sn to those of single-particle states in 133Sn determined in a recent measurement of the 132Sn(d, p)133Sn reaction. We found a significant reduction of the energy splitting of the weakly bound 3p orbits compared to the well-bound 2d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations using a one-body spin-orbit interaction and a Woods–Saxon potential of standard radius and diffuseness. The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of the weakly bound orbits, without invoking a weakening of the spin-orbit strength. Keywords: Nuclear structure, Spin-orbit interaction, Transfer reactions, Doubly-magic nuclei, Shell model

Certain astrophysical environments such as thermonuclear outbursts on accreting neutron stars (Type-I X-ray bursts) are hot enough to allow for breakout from the Hot CNO hydrogen burning cycles to the rapid proton capture (rp) process. An important breakout reaction sequence is 15O(α,γ)19Ne(p,γ)20Na and the 19Ne(p,γ)20Na reaction rate is expected to be dominated by a single resonance at 457 keV above the proton threshold in 20Na. The resonance strength and, hence, reaction rate depends strongly on whether this 20Na state at an excitation energy of 2647 keV has spin and parity of 1 + or 3 + . Previous 20Mg ( J π = 0 + ) β + decay experiments have relied almost entirely on searches for β-delayed proton emission from this resonance in 20Na to limit the log ft value and, hence, J π . However there is a non-negligible γ-ray branch expected that must also be limited experimentally to determine the log ft value and constrain J π . We have measured the β-delayed γ decay of 20Mg to complement previous β-delayed proton decay work and provide the first complete limit based on all energetically allowed decay channels through the 2647 keV state. Our limit confirms that a 1 + assignment for this state is highly unlikely.

The structure of nuclei provides insight into astrophysical reaction rates that are difficult to measure directly. These studies are often performed with transfer reactions and β-decay measurements. These experiments benefit from particle-γ coincidence measurements which provide information beyond that of particle detection alone. The Hybrid Array of Gamma Ray Detectors (HAGRiD) of LaBr3(Ce) scintillators has been designed with this purpose in mind. The design of the array permits it to be coupled with particle detector systems, such as the Oak Ridge Rutgers University Barrel Array (ORRUBA) of silicon detectors and the Versatile Array of Neutron Detectors at Low Energy (VANDLE). It is also designed to operate with the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) advanced target system. HAGRiD’s design avoids compromising the charged-particle angular resolution due to compact geometries which are often used to increase the γ efficiency in other systems. First experiments with HAGRiD coupled to VANDLE as well as ORRUBA and JENSA are discussed.

A recoil mass separator SECAR has been designed for the purpose of studying low-energy ( p , γ ) and ( α , γ ) reactions in inverse kinematics with radioactive beams for masses up to about A = 65. Their reaction rates are of importance for our understanding of the energy production and nucleosynthesis during explosive hydrogen and helium burning. The radiative capture reactions take place in a windowless hydrogen or He gas target at the entrance of the separator, which consists of four Sections . The first Section selects the charge state of the recoils. The second and third Sections contain Wien Filters providing high mass resolving power to separate efficiently the intense beam from the few reaction products. In the following fourth Section , the reaction products are guided into a detector system capable of position, angle and time-of-flight measurements. In order to accept the complete kinematic cone of recoil particles including multiple scattering in the target in the center of mass energy range of 0.2 MeV to 3.0 MeV, the system must have a large polar angle acceptance of ± 25 mrad. This requires a careful minimization of higher order aberrations. The present system will be installed at the NSCL ReA3 accelerator and will be used with the much higher beam intensities of the FRIB facility when it becomes available.

Explosive stellar environments are sometimes driven by nuclear reactions on short-lived, radioactive nuclei. These reactions often drive the stellar explosion, alter the observable light curves produced, and dictate the final abundances of the isotopes created. Unfortunately, many reaction rates at stellar temperatures cannot be directly measured in the laboratory, due to the physical limitations of ultra-low cross sections and high background rates. An additional complication arises because many of the important reactions involve radioactive nuclei which have lifetimes too short to be made into a target. As such, direct reactions require very intense and pure beams of exotic nuclei. Indirect approaches with both stable and radioactive beams can, however, provide crucial information on the nuclei involved in these astrophysical reactions. A major development toward both direct and indirect studies of nuclear reactions rates is the commissioning of the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) supersonic gas jet target. The JENSA system provides a pure, homogeneous, highly localized, dense, and robust gaseous target for radioactive ion beam studies. Charged-particle reactions measurements made with gas jet targets can be cleaner and display better resolution than with traditional targets. With the availability of pure and localized gas jet targets in combination with developments in exotic radioactive ion beams and next-generation detector systems, the range of reaction studies that are experimentally possible is vastly expanded. Various representative cases will be discussed.

An improved method for preparation of self-supporting deuterated polyethylene targets using solvent casting technique is described. The improved method provides recommendations for solvent heating, solvent casting of the thin film, and subsequent heating treatment which is shown to greatly enhance the overall target strength and durability as needed for accelerator experiments. A detailed characterization using both optical and electron microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy demonstrates the improvements using the post-casting heating treatment. The effects of heavy ion-induced target degradation and recommendations for use under these conditions is also discussed.

GODDESS is a coupling of the charged-particle detection system ORRUBA to the gamma-ray detector array Gammasphere. This coupling has been developed in order to facilitate the high-resolution measurement of direct reactions in normal and inverse kinematics with stable and radioactive beams. GODDESS has been commissioned using a beam of 134 Xe at 10 MeV/A, in a campaign of stable beam measurements. The measurement demonstrates the capabilities of GODDESS under radioactive beam conditions, and provides the first data on the single-neutron states in 135 Xe, including previously unobserved states based on the orbitals above the N=82 shell closure.

Results are presented from the first neutron-transfer measurement on $^{80}\mathrm{Ge}$ using an exotic beam from the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Newly measured spins and spectroscopic factors of low-lying states of $^{81}\mathrm{Ge}$ are determined, and the neutron capture cross section on $^{80}\mathrm{Ge}$ was calculated in a direct-semidirect model to provide a more realistic ($n,\ensuremath{\gamma}$) reaction rate for $r$-process simulations. Furthermore, a region of shape coexistence around $N\ensuremath{\approx}50$ is confirmed and implications for the magic nature of $^{78}\mathrm{Ni}$ are discussed.

During the slow neutron capture process in massive stars, reactions on light elements can both produce and absorb neutrons thereby influencing the final heavy element abundances. At low metallicities, the high neutron capture rate of 16-O can inhibit s-process nucleosynthesis unless the neutrons are recycled via the 17O(a,n)20Ne reaction. The efficiency of this neutron recycling is determined by competition between the 17O(a,n)20Ne and 17O(a,g)21Ne reactions. While some experimental data are available on the former reaction, no data exist for the radiative capture channel at the relevant astrophysical energies. The 17O(a,g)21Ne reaction has been studied directly using the DRAGON recoil separator at the TRIUMF Laboratory. The reaction cross section has been determined at energies between 0.6 and 1.6 MeV Ecm, reaching into the Gamow window for core helium burning for the first time. Resonance strengths for resonances at 0.63, 0.721, 0.81 and 1.122 MeV Ecm have been extracted. The experimentally based reaction rate calculated represents a lower limit, but suggests that significant s-process nucleosynthesis occurs in low metallicity massive stars., 7 pages, 5 figures

Background: The $^{15}\mathrm{O}(\ensuremath{\alpha},\ensuremath{\gamma})^{19}\mathrm{Ne}$ bottleneck reaction in Type I x-ray bursts is the most important thermonuclear reaction rate to constrain experimentally, to improve the accuracy of burst light-curve simulations. A proposed technique to determine the thermonuclear rate of this reaction employs the $^{20}\mathrm{Mg}(\ensuremath{\beta}p\ensuremath{\alpha})^{15}\mathrm{O}$ decay sequence. The key $^{15}\mathrm{O}(\ensuremath{\alpha},\ensuremath{\gamma})^{19}\mathrm{Ne}$ resonance at an excitation of 4.03 MeV is now known to be fed in $^{20}\mathrm{Mg}(\ensuremath{\beta}p\ensuremath{\gamma})^{19}\mathrm{Ne}$; however, the energies of the protons feeding the 4.03 MeV state are unknown. Knowledge of the proton energies will facilitate future $^{20}\mathrm{Mg}(\ensuremath{\beta}p\ensuremath{\alpha})^{15}\mathrm{O}$ measurements.Purpose: To determine the energy of the proton transition feeding the 4.03 MeV state in $^{19}\mathrm{Ne}$.Method: A fast beam of $^{20}\mathrm{Mg}$ was implanted into a plastic scintillator, which was used to detect $\ensuremath{\beta}$ particles. 16 high purity germanium detectors were used to detect $\ensuremath{\gamma}$ rays emitted following $\ensuremath{\beta}p$ decay. A Monte Carlo method was used to simulate the Doppler broadening of $^{19}\mathrm{Ne}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray lines and compare to the experimental data.Results: The center of mass energy between the proton and $^{19}\mathrm{Ne}$, feeding the 4.03 MeV state, is measured to be $1.21{}_{\ensuremath{-}0.22}^{+0.25}\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$, corresponding to a $^{20}\mathrm{Na}$ excitation energy of $7.44{}_{\ensuremath{-}0.22}^{+0.25}\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. Absolute feeding intensities and $\ensuremath{\gamma}$-decay branching ratios of $^{19}\mathrm{Ne}$ states were determined including the 1615 keV state, which has not been observed before in this decay. A new $\ensuremath{\gamma}$ decay branch from the 1536 keV state in $^{19}\mathrm{Ne}$ to the ground state is reported. The lifetime of the 1507 keV state in $^{19}\mathrm{Ne}$ is measured to be $4.3{}_{\ensuremath{-}1.1}^{+1.3}$ ps resolving discrepancies in the literature. Conflicting $^{20}\mathrm{Mg}(\ensuremath{\beta}p$) decay schemes in published literature are clarified.Conclusions: The utility of this Doppler broadening technique to provide information on $\ensuremath{\beta}$-delayed nucleon emission and excited-state lifetimes has been further demonstrated. In particular, knowledge of the proton energies feeding the 4.03 MeV $^{19}\mathrm{Ne}$ state in $^{20}\mathrm{Mg}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay will facilitate future measurements of the $\ensuremath{\alpha}$-particle branching ratio.

The astrophysical $S$-factor for the radiative proton capture reaction on $^7$Be ($S_{17}$) at low energies is affected by the $s$-wave scattering lengths. We report the measurement of elastic and inelastic scattering cross sections for the $^7$Be+p system in the center-of-mass energy range 0.474 - 2.740 MeV and center-of-mass angular range of 70$^\circ$- 150$^\circ$. A radioactive $^7$Be beam produced at Oak Ridge National Laboratory's (ORNL) Holifield Radioactive Ion Beam Facility was accelerated and bombarded a thin polypropylene (CH$_{2}$)$_\text n$ target. Scattered ions were detected in the segmented Silicon Detector Array. Using an $\textit{R}$-matrix analysis of ORNL and Louvain-la-Neuve cross section data, the $s$-wave scattering lengths for channel spins 1 and 2 were determined to be 17.34$^{+1.11}_{-1.33}$ and -3.18$^{+0.55}_{-0.50}$ fm, respectively. The uncertainty in the $s$-wave scattering lengths reported in this work is smaller by a factor of 5-8 compared to the previous measurement, which may reduce the overall uncertainty in $S_{17}$ at zero energy. The level structure of $^8$B is discussed based upon the results from this work. Evidence for the existence of 0$^+$ and 2$^+$ levels in $^8$B at 1.9 and 2.21 MeV, respectively, is observed.

Half of the elements heavier than iron are believed to be produced through the rapid neutron-capture process ($r$ process). The astrophysical environment(s) where the $r$ process occurs remains an open question, even after recent observations of neutron-star mergers and the associated kilonova. Features in the abundance pattern of $r$-process ashes may provide critical insight for distinguishing contributions from different possible sites, including neutron-star mergers and core-collapse supernovae. In particular, the largely unknown neutron-capture reaction rates on neutron-rich unstable nuclei near $^{132}\mathrm{Sn}$ could have a significant impact on the final $r$-process abundances. To better determine these neutron-capture rates, the $(d,p)$ reaction has been measured in inverse kinematics using radioactive ion beams of $^{126}\mathrm{Sn}$ and $^{128}\mathrm{Sn}$ and a stable beam of $^{124}\mathrm{Sn}$ interacting with a ${({\mathrm{CD}}_{2})}_{n}$ target. An array of position-sensitive silicon strip detectors, including the Super Oak Ridge Rutgers University Barrel Array, was used to detect light reaction products. In addition to the present measurements, previous measurements of $^{130,132}\mathrm{Sn}(d,p)$ were reanalyzed using state-of-the-art reaction theory to extract a consistent set of spectroscopic factors for $(d,p)$ reactions on even tin nuclei between the heaviest stable isotope $^{124}\mathrm{Sn}$ and doubly magic $^{132}\mathrm{Sn}$. The spectroscopic information was used to calculate direct-semidirect $(n,\ensuremath{\gamma})$ cross sections, which will serve as important input for $r$-process abundance calculations.

The $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne reaction is responsible for breakout from the hot CNO cycle in Type I x-ray bursts. Understanding the properties of resonances between $E_x = 4$ and 5 MeV in $^{19}$Ne is crucial in the calculation of this reaction rate. The spins and parities of these states are well known, with the exception of the 4.14- and 4.20-MeV states, which have adopted spin-parities of 9/2$^-$ and 7/2$^-$, respectively. Gamma-ray transitions from these states were studied using triton-$\gamma$-$\gamma$ coincidences from the $^{19}$F($^{3}$He,$t\gamma$)$^{19}$Ne reaction measured with GODDESS (Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory. The observed transitions from the 4.14- and 4.20-MeV states provide strong evidence that the $J^\pi$ values are actually 7/2$^-$ and 9/2$^-$, respectively. These assignments are consistent with the values in the $^{19}$F mirror nucleus and in contrast to previously accepted assignments.

Compton γ -ray sources have been in operation for over 30 years with new facilities being under construction or proposed. The gamma beam system under implementation at the Extreme Light Infrastructure - Nuclear Physics facility in Romania will deliver brilliant γ -ray beams with energies up to 19.5 MeV. Several instruments for measuring the parameters of the γ -ray beam are under development at ELI-NP. One of these instruments based on a High Purity Germanium detector is routinely used for beam energy measurements at other facilities. Here we investigate the use of a High Purity Germanium detector to continuously monitor the intensity of the ELI-NP gamma beam by measuring the inelastic scattering of photons. This method relies on both experimental and simulated data and it has been successfully tested during a recent experiment at the High Intensity γ -ray Source facility.

In radioactive ion beam experiments, beams containing isomers can be of interest in probing nuclear structure and informing astrophysical reaction rates. While the production of mixed in-flight ground state and isomer beams using nucleon transfer can be generally understood through distorted wave Born approximation methodology, low-spin isomer production via fast fragmentation is relatively unstudied. To attain a practical understanding of low-spin isomer production using fast fragmentation beams, a test case of $^{38}\mathrm{K}/^{38m}\mathrm{K}$ was studied at the National Superconducting Cyclotron Laboratory's ReAccelerated Beam facility. Starting from lise++ predictions, the fragmentation momentum distribution was sampled to determine isomer production. In addition, the effects of the gas stopper gradient and charge breeding times were examined. In the case of $^{38}\mathrm{K}$, isomer production peaks at $\ensuremath{\sim}57%$. This maximum is observed just off the lise++ predicted optimum magnetic rigidity, with only small losses in beam intensity within a few percent of this optimum rigidity setting. Control of the isomer fraction was also achieved through the modification of charge breeding times. Fast fragmentation appears to be a feasible method for production of low-spin isomeric beams, but additional study is necessary to better describe the mechanism involved.

An array consisting of 12 deuterated organic liquid scintillator detectors for fast-neutron spectroscopy was designed and built at Oak Ridge National Laboratory (ORNL). This versatile array is designed for measurements with low reaction yields, such as those performed with rare isotope beams, as well as at high current DC facilities used for underground nuclear astrophysics research. Because some measurements also offer limited, or no, additional timing information, the ORNL Deuterated Spectroscopic Array (ODeSA) was optimized to utilize spectrum unfolding to extract neutron energy spectra . This array was characterized for n/ γ pulse shape discrimination, light response, resolution, and intrinsic efficiency by using the neutron time-of-flight tunnel at the Edwards Accelerator Laboratory at Ohio University. Results and future plans are discussed.

Background: $^{32}\mathrm{Cl}$ is a neutron-deficient isotope with a $\ensuremath{\beta}$-decay half-life of 298 ms and a spin and parity of ${J}^{\ensuremath{\pi}}={1}^{+}$. Previous measurements of $^{32}\mathrm{Cl} \ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays have yielded a $\ensuremath{\beta}$-decay scheme with twelve $\ensuremath{\beta}$-decay transitions, contributing to studies of nuclear structure and fundamental symmetries. Those experiments have been limited to the observation of $^{32}\mathrm{S}$ states with ${J}^{\ensuremath{\pi}}={0}^{+},{1}^{+},{2}^{+}$.Purpose: Our goal is to search for new $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays and $\ensuremath{\beta}$-decay transitions of $^{32}\mathrm{Cl}$ to $^{32}\mathrm{S}$.Methods: A measurement of $^{32}\mathrm{Cl} \ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ decay has been performed using the Clovershare array of high-purity germanium detectors at the National Superconducting Cyclotron Laboratory.Results: By acquiring the highest-statistics $^{32}\mathrm{Cl} \ensuremath{\beta}$-delayed $\ensuremath{\gamma}$-ray spectrum to date and exploiting a new sensitivity to $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, this experiment has enabled the observation of nine previously unobserved $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$-ray transitions, leading to the inference of five $\ensuremath{\beta}$-decay transitions never before observed in $^{32}\mathrm{Cl} \ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ decay. The set of observed states includes negative-parity states for the first time. By combining the new information with data from previous work, the lifetimes and partial widths of the 8861- and 9650-keV states of $^{32}\mathrm{S}$ have been determined. In addition, the $^{31}\mathrm{P}(p,\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{28}\mathrm{Si}$ resonance strength of the 9650-keV state has been limited to $\ensuremath{\omega}\ensuremath{\gamma}l9.8$ meV, which is an improvement over direct measurements.Conclusion: An enhanced decay scheme has been constructed. Most of the excited bound $^{32}\mathrm{S}$ states that would correspond to allowed and first-forbidden $\ensuremath{\beta}$-decay transitions have been observed, demonstrating the potential of $\ensuremath{\beta}$-decay experiments to approach complete spectroscopy measurements at the next generation of radioactive beam facilities. The observed positive-parity levels are well matched by $sd$ shell-model calculations.

The JENSA gas-jet target was designed for experiments with radioactive beams provided by the rare isotope re-accelerator ReA3 at the National Superconducting Cyclotron Laboratory. The gas jet will be the main target for the Separator for Capture Reactions SECAR at the Facility for Rare Isotope Beams on the campus of Michigan State University, USA. In this work, we describe the advantages of a gas-jet target, detail the current recirculating gas system, and report recent measurements of helium jet thicknesses of up to about $10^{19}$ atoms/cm$^2$. Finally a comparison with other supersonic gas-jet targets is presented., Comment: Preprint, submitted to Nuclear Instruments and Methods in Physics Research A. $\copyright$ 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license

A recoil separator SECAR has been designed to study radiative capture reactions relevant for the astrophysical rp-process in inverse kinematics for the Facility for Rare Isotope Beams (FRIB). We describe the design, layout, and ion optics of the recoil separator and present the status of the project.

The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas-jet target was used to perform spectroscopic studies of $^{20}\mathrm{Ne}+p$ reactions. Levels in $^{19}\mathrm{Ne}$ were probed via the $^{20}\mathrm{Ne}(p,d)^{19}\mathrm{Ne}$ reaction to constrain the astrophysical rate of the $^{18}\mathrm{F}(p,\ensuremath{\alpha})^{15}\mathrm{O}$ reaction. Additionally, the first spectroscopic study of the $^{20}\mathrm{Ne}(p,^{3}\mathrm{He})^{18}\mathrm{F}$ reaction was performed. Angular distribution data were used to determine or confirm the spins of several previously observed levels, and the existence of a strong subthreshold $^{18}\mathrm{F}(p,\ensuremath{\alpha})^{15}\mathrm{O}$ resonance was verified.

The $^{15}\mathrm{O}(\ensuremath{\alpha},\ensuremath{\gamma})^{19}\mathrm{Ne}$ reaction is expected to trigger the initial path for breakout from the CNO hydrogen-burning cycles to the rapid proton capture $(rp)$ process in type I x-ray bursts on accreting neutron stars. The thermonuclear reaction rate has a major impact on models of type I x-ray burst observables and it depends on the small $\ensuremath{\alpha}$-particle branching ratio, ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}/\mathrm{\ensuremath{\Gamma}}$, of the 4.03 MeV state in $^{19}\mathrm{Ne}$. Attempts to measure ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}/\mathrm{\ensuremath{\Gamma}}$ by populating the 4.03 MeV state using nuclear reactions have only led to strong upper limits. In the present work, we report the first experimental evidence that the 4.03 MeV $^{19}\mathrm{Ne}$ state is populated in $^{20}\mathrm{Mg} \ensuremath{\beta}$-delayed proton emission. This new channel has the potential to provide the necessary sensitivity to detect a finite value of ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}/\mathrm{\ensuremath{\Gamma}}$.

We report the independent experimental confirmation of an isomeric state in the proton drip-line nucleus $^{26}$P. The ${\gamma}$-ray energy and half-life determined are 164.4 $\pm$ 0.3 (sys) $\pm$ 0.2 (stat) keV and 104 $\pm$ 14 ns, respectively, which are in agreement with the previously reported values. These values are used to set a semi-empirical limit on the proton separation energy of $^{26}$P, with the conclusion that it can be bound or unbound., Comment: 5 pages, 3 figures

Of particular interest in astrophysics is the $^{34}\mathrm{S}(p,\ensuremath{\gamma})^{35}\mathrm{Cl}$ reaction, which serves as a stepping stone in thermonuclear runaway reaction chains during a nova explosion. Though the isotopes involved are all stable, the reaction rate of this significant step is not well known, due to a lack of experimental spectroscopic information on states within the Gamow window above the proton separation threshold of $^{35}\mathrm{Cl}$. Measurements of level spins and parities provide input for the calculation of resonance strengths, which ultimately determine the astrophysical reaction rate of the $^{34}\mathrm{S}(p,\ensuremath{\gamma})^{35}\mathrm{Cl}$ proton capture reaction. By performing the $^{37}\mathrm{Cl}(p,t)^{35}\mathrm{Cl}$ reaction in normal kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory, we have conducted a study of the region of astrophysical interest in $^{35}\mathrm{Cl}$, and have made the first-ever constraint on the spin and parity assignment for a level at $6677\ifmmode\pm\else\textpm\fi{}15$ keV $({E}_{r}=306$ keV), inside the Gamow window for novae.

Background: Transfer reactions are a useful tool for studying nuclear structure, particularly in the regime of low level densities and strong single-particle strengths. In addition, transfer reactions can populate levels above particle decay thresholds, allowing for the possibility of studying the subsequent decays and furthering our understanding of the nuclei being probed. In particular, the decay of loosely bound nuclei such as $^{12}\mathrm{N}$ can help inform and improve structure models.Purpose: To learn about the decay of excited states in $^{12}\mathrm{N}$, to more generally inform nuclear structure models, particularly in the case of particle-unbound levels in low-mass systems which are within the reach of state-of-the-art ab initio calculations.Method: In this follow-up analysis of previously published data [Chipps et al. (JENSA Collaboration), Phys. Rev. C 92, 034325 (2015)], decay particles from excited states populated in $^{12}\mathrm{N}$ have been detected in coincidence with tritons from the $^{14}\mathrm{N}(p,t)^{12}\mathrm{N}$ transfer reaction. Specifically, decay protons from proton-unbound levels above $\ensuremath{\sim}2$ MeV excitation energy were observed by utilizing the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target.Results: Isotropic proton branching ratios for the $p0$ and $p1$ decay channels are calculated and decay particle spectra for the populated levels from $p0$, $p1$, and $p2$ decay are given.Conclusions: The current data from $^{14}\mathrm{N}(p,t)^{12}\mathrm{N}$ will help provide nuclear structure and decay information input to models in this mass region.

When a neutron star accretes hydrogen and helium from the outer layers of its companion star, thermonuclear burning enables the α p-process as a break out mechanism from the hot CNO cycle. Model calculations predict ( α , p) reaction rates significantly affect both the light curves and elemental abundances in the burst ashes. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target enables the direct measurement of previously inaccessible ( α ,p) reactions with radioactive beams provided by the rare isotope re-accelerator ReA3 at the National Superconducting Cyclotron Laboratory (NSCL), USA. JENSA is going to be the main target for the Recoil Separator for Capture Reactions (SECAR) at the Facility for Rare Isotope Beams (FRIB). Commissioning of JENSA and first experiments at Oak Ridge National Laboratory (ORNL) showed a highly localized, pure gas target with a density of ∼10 19 atoms per square centimeter. Preliminary results are presented from the first direct cross section measurement of the 34 Ar( α , p) 37 K reaction at NSCL.

Background: Measurements of $\ensuremath{\beta}$ decay provide important nuclear structure information that can be used to probe isospin asymmetries and inform nuclear astrophysics studies.Purpose: To measure the $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ decay of $^{26}\text{P}$ and compare the results with previous experimental results and shell-model calculations.Method: A $^{26}\text{P}$ fast beam produced using nuclear fragmentation was implanted into a planar germanium detector. Its $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$-ray emission was measured with an array of 16 high-purity germanium detectors. Positrons emitted in the decay were detected in coincidence to reduce the background.Results: The absolute intensities of $^{26}\text{P}\phantom{\rule{4.pt}{0ex}}\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays were determined. A total of six new $\ensuremath{\beta}$-decay branches and 15 new $\ensuremath{\gamma}$-ray lines have been observed for the first time in $^{26}\text{P}\phantom{\rule{4.pt}{0ex}}\ensuremath{\beta}$ decay. A complete $\ensuremath{\beta}$-decay scheme was built for the allowed transitions to bound excited states of $^{26}\text{Si}$. $ft$ values and Gamow-Teller strengths were also determined for these transitions and compared with shell-model calculations and the mirror $\ensuremath{\beta}$ decay of $^{26}\text{Na}$, revealing significant mirror asymmetries.Conclusions: A very good agreement with theoretical predictions based on the USDB shell model is observed. The significant mirror asymmetry observed for the transition to the first excited state $(\ensuremath{\delta}=51(10)%)$ may be evidence for a proton halo in $^{26}\text{P}$.

The thermonuclear ^{30}P(p,γ)^{31}S reaction rate is critical for modeling the final elemental and isotopic abundances of ONe nova nucleosynthesis, which affect the calibration of proposed nova thermometers and the identification of presolar nova grains, respectively. Unfortunately, the rate of this reaction is essentially unconstrained experimentally, because the strengths of key ^{31}S proton capture resonance states are not known, largely due to uncertainties in their spins and parities. Using the β decay of ^{31}Cl, we have observed the β-delayed γ decay of a ^{31}S state at E_{x}=6390.2(7) keV, with a ^{30}P(p,γ)^{31}S resonance energy of E_{r}=259.3(8) keV, in the middle of the ^{30}P(p,γ)^{31}S Gamow window for peak nova temperatures. This state exhibits isospin mixing with the nearby isobaric analog state at E_{x}=6279.0(6) keV, giving it an unambiguous spin and parity of 3/2^{+} and making it an important l=0 resonance for proton capture on ^{30}P.

$^{26}\mathrm{Al}$ remains an intriguing target for observational $\ensuremath{\gamma}$-ray astronomy, thanks to its characteristic decay. The $^{25}\mathrm{Al}(p,\ensuremath{\gamma})^{26}\mathrm{Si}$ reaction is the crucial link in a sequence that bypasses the production of the observable $^{26}\mathrm{Al}^{g}$ in favor of the short-lived isomeric state; determining its astrophysical reaction rate across a range of stellar environments has been the focus of many studies. A reanalysis of previous work, utilizing recent improvements in excitation energies and ground state masses, is presented to reduce the ambiguities in the literature and provide focus to future measurements.

An unexpected breakdown of the isobaric multiplet mass equation in the $A=20$, $T=2$ quintet was recently reported, presenting a challenge to modern theories of nuclear structure. In the present work, the excitation energy of the lowest $T = 2$ state in $^{20}$Na has been measured to be $6498.4 \pm 0.2_{\textrm{stat}} \pm 0.4_{\textrm{syst}}$ keV by using the superallowed $0^+ \rightarrow 0^+$ beta decay of $^{20}$Mg to access it and an array of high-purity germanium detectors to detect its $\gamma$-ray deexcitation. This value differs by 27 keV (1.9 standard deviations) from the recommended value of $6525 \pm 14$ keV and is a factor of 28 more precise. The isobaric multiplet mass equation is shown to be revalidated when the new value is adopted., Comment: 5 pages, 5 figures

Classical novae are expected to contribute to the 1809-keV Galactic $\ensuremath{\gamma}$-ray emission by producing its precursor $^{26}\mathrm{Al}$, but the yield depends on the thermonuclear rate of the unmeasured $^{25}\mathrm{Al}(p,\ensuremath{\gamma})^{26}\mathrm{Si}$ reaction. Using the $\ensuremath{\beta}$ decay of $^{26}\mathrm{P}$ to populate the key ${J}^{\ensuremath{\pi}}={3}^{+}$ resonance in this reaction, we report the first evidence for the observation of its exit channel via a $1741.6\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{syst})\text{ }\text{ }\mathrm{keV}$ primary $\ensuremath{\gamma}$ ray, where the uncertainties are statistical and systematic, respectively. By combining the measured $\ensuremath{\gamma}$-ray energy and intensity with other experimental data on $^{26}\mathrm{Si}$, we find the center-of-mass energy and strength of the resonance to be ${E}_{r}=414.9\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{lit}.)\text{ }\text{ }\mathrm{keV}$ and $\ensuremath{\omega}\ensuremath{\gamma}=23\ifmmode\pm\else\textpm\fi{}6(\mathrm{stat}{)}_{\ensuremath{-}10}^{+11}(\mathrm{lit}.)\text{ }\text{ }\mathrm{meV}$, respectively, where the last uncertainties are from adopted literature data. We use hydrodynamic nova simulations to model $^{26}\mathrm{Al}$ production showing that these measurements effectively eliminate the dominant experimental nuclear-physics uncertainty and we estimate that novae may contribute up to 30% of the Galactic $^{26}\mathrm{Al}$.

The extraction of detailed nuclear structure information from transfer reactions requires reliable, well-normalized data as well as optical potentials and a theoretical framework demonstrated to work well in the relevant mass and beam energy ranges. It is rare that the theoretical ingredients can be tested well for exotic nuclei owing to the paucity of data. The halo nucleus Be-11 has been examined through the 10Be(d,p) reaction in inverse kinematics at equivalent deuteron energies of 12,15,18, and 21.4 MeV. Elastic scattering of Be-10 on protons was used to select optical potentials for the analysis of the transfer data. Additionally, data from the elastic and inelastic scattering of Be-10 on deuterons was used to fit optical potentials at the four measured energies. Transfers to the two bound states and the first resonance in Be-11 were analyzed using the Finite Range ADiabatic Wave Approximation (FR-ADWA). Consistent values of the spectroscopic factor of both the ground and first excited states were extracted from the four measurements, with average values of 0.71(5) and 0.62(4) respectively. The calculations for transfer to the first resonance were found to be sensitive to the size of the energy bin used and therefore could not be used to extract a spectroscopic factor., 16 Pages, 10 figures

The best examples of halo nuclei, exotic systems with a diffuse nuclear cloud surrounding a tightly-bound core, are found in the light, neutron-rich region, where the halo neutrons experience only weak binding and a weak, or no, potential barrier. Modern direct reaction measurement techniques provide powerful probes of the structure of exotic nuclei. Despite more than four decades of these studies on the benchmark one-neutron halo nucleus Be-11, the spectroscopic factors for the two bound states remain poorly constrained. In the present work, the Be-10(d,p) reaction has been used in inverse kinematics at four beam energies to study the structure of Be-11. The spectroscopic factors extracted using the adiabatic model, were found to be consistent across the four measurements, and were largely insensitive to the optical potential used. The extracted spectroscopic factor for a neutron in a nlj = 2s1/2 state coupled to the ground state of Be-10 is 0.71(5). For the first excited state at 0.32 MeV, a spectroscopic factor of 0.62(4) is found for the halo neutron in a 1p1/2 state., 5 pages, 4 figures

International audience; A study of the 10Be(4He,4He)10Be reaction has been performed at 10Be beam energies of 25.0, 27.0, 29.0, 32.0, 34.0, 38.0, 40.0, 42.0, 44.0 and 46.0 MeV. The measurements were to explore possible molecular rotational bands in 14C. Three states at excitation energies of Ex = 18.8, 19.76 and 20.66 MeV have been measured and their spins have been determined to be 5−, 5− and 6+, respectively.

The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of 132Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the cross section. The magnitude of the nuclear effects was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p1/2 state expected above the N=82 shell closure. The data were analyzed using finite range adiabatic wave calculations and the results compared with the previous analysis using the distorted wave Born approximation. Angular distributions for the ground and first excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one neutron states beyond the benchmark doubly-magic nucleus 208Pb., Comment: 22 pages, 7 figures

Atomic nuclei have a shell structure where nuclei with 'magic numbers' of neutrons and protons are analogous to the noble gases in atomic physics. Only ten nuclei with the standard magic numbers of both neutrons and protons have so far been observed. The nuclear shell model is founded on the precept that neutrons and protons can move as independent particles in orbitals with discrete quantum numbers, subject to a mean field generated by all the other nucleons. Knowledge of the properties of single-particle states outside nuclear shell closures in exotic nuclei is important for a fundamental understanding of nuclear structure and nucleosynthesis (for example the r-process, which is responsible for the production of about half of the heavy elements). However, as a result of their short lifetimes, there is a paucity of knowledge about the nature of single-particle states outside exotic doubly magic nuclei. Here we measure the single-particle character of the levels in 133Sn that lie outside the double shell closure present at the short-lived nucleus 132Sn. We use an inverse kinematics technique that involves the transfer of a single nucleon to the nucleus. The purity of the measured single-particle states clearly illustrates the magic nature of 132Sn., 19 pages, 5 figures and 4 tables

The cluster structure of 12 C is explored and recent measurements of proton inelastic scattering, suggesting a 2+ state close to 9.6 MeV are presented. Resonant scattering studies of 10 Be + 4 He used to populate resonances in 14 C are briefly discussed.