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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.

The astrophysical F 18 ( p , α ) O 15 rate determines, in large part, the extent to which the observable radioisotope 18 F is produced in novae. This rate, however, has been extremely uncertain owing to the unknown properties of a strong subthreshold resonance and its possible interference with higher-lying resonances. The new Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas-jet target has been used for the first time to determine the spin of this important resonance and significantly reduce uncertainties in the F 18 ( p , α ) O 15 rate.

To take full advantage of advanced exotic beam facilities, target technology must also be advanced. Particularly important to the study of astrophysical reaction rates is the creation of localized and dense targets of hydrogen and helium. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas-jet target has been constructed for this purpose. JENSA was constructed at Oak Ridge National Laboratory (ORNL) where it was tested and characterized, and has now moved to the ReA3 reaccelerated beam hall at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University for use with radioactive beams.

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.

The 15O(α,γ)19Ne reaction is an important trigger reaction leading to the rapid proton (rp) capture process in X-ray bursts. The primary uncertainty in determining its astrophysical rate is the uncertain α branching ratios of levels near Ex = 4.1 MeV in 19Ne. These states have been populated in a study of the 20Ne(p, d)19Ne reaction, and α branching ratios are reported in this manuscript.

The tin chain of isotopes provides a unique region in which to investigate the evolution of single-particle structure, spreading from N = 50 at 100Sn, through 10 stable isotopes and the N = 82 shell closure at 132Sn out into the r-process path. Direct reactions performed on radioactive ion beams are sensitive spectroscopic tools for studying exotic nuclei. Here we present one experiment knocking out neutrons from tin isotopes that are already neutron deficient and two reactions that add a neutron to neutron-rich 130Sn. Both techniques rely on selective particle identification and the measurement of γ rays in coincidence with charged ions. We present the goals of the two experiments and the particle identification for the channels of interest. The final results will be presented in future publications.

The study of nuclei far from stability elucidates the evolution of nuclear shell structure, and also affects estimates of heavy element nucleosynthesis in supernova explosions. Measurement of transfer reactions in inverse kinematics with radioactive ion beams is a powerful technique for these types of studies. Rare isotope beams often have relatively low intensities, and this places difficult requirements on the detection systems for reaction products. The detectors must provide large solid angle coverage in the laboratory along with good position and energy resolution. The Super ORRUBA detector array has been developed for such measurements and is comprised of 18 double-sided, nonresistive silicon strip detectors. This configuration features low thresholds and improved resolution over detectors employing charge division. As a first implementation of this system, the 80Ge(d,p)81Ge neutron transfer reaction in inverse kinematics was measured at HRIBF at ORNL, to determine the properties of levels in 81Ge.

The (d, p) reaction was measured with the radioactive ion beams of 126Sn and 128Sn in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory, utilizing the Super ORRUBA silicon detector array. Angular distributions of reaction protons were measured for several states in 127Sn and 129Sn to determine angular momentum transfers and deduce spectroscopic factors. Such information is critical for calculating direct (n,γ) cross sections for the r-process as well as for constraining shell model parameters in the A≈130 region. Combined with previous experiments on 130Sn and 132Sn, these results will provide a complete set of (d, p) reaction data on even tin isotopes between stable 124Sn and doubly-magic 132Sn.

The astrophysical rapid neutron-capture process (r-process) is believed to have produced approximately half of the nuclear species more massive than Fe. Unfortunately, almost nothing is known about the structure of the majority of the extremely neutron-rich nuclei involved in the reaction flow. At exotic beam facilities such as the Holifield Radioactive Ion Beam Facility (HRIBF), measurements with accelerated beams of fission fragments have provided some of the first spectroscopic information on many r-process nuclei. The new SuperORRUBA (Oak Ridge Rutgers University Barrel Array) detector has been constructed at the HRIBF to study such nuclei, and first results are presented.

Galactic 26Al is the first radioactive nucleus to be positively identified by -ray astronomy with detection of the 1.809 MeV ray associated with its decay. This nucleus is destroyed in astrophysical environments in the 26Al(p, )27Si and inelastic 26Al+p scattering reactions where properties of 27Si levels determine reaction rates. To investigate these properties, elastic and inelastic 26Al+p scattering reactions were measured between Ec.m. = 0.5 1.5 MeV at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL). A candidate for a new resonance in the 26Al(p, )27Si reaction was identified. Upper limits were also set on the strengths of postulated resonances and on the cross section of the inelastic reaction, but there is little effect on current reaction rate calculations.

A recent discussion of theoretical work on the ${}^{25}$Al($p,\ensuremath{\gamma}$)${}^{26}$Si astrophysical reaction rate [W.A. Richter, B. Alex Brown, A. Signoracci and M. Wiescher, Phys. Rev. C 83, 065803 (2011)] omits some current and relevant experimental information in forming its scientific conclusions. Accounting for this new information has the potential to significantly alter the reaction rate derived in the paper.

Big Bang nucleosynthesis calculations, constrained by the Wilkinson Microwave Anisotropy Probe results, produce {sup 7}Li abundances almost a factor of four larger than those extrapolated from observations. Since primordial {sup 7}Li is believed to be mostly produced by the beta decay of {sup 7}Be, one proposed solution to this discrepancy is a resonant enhancement of the {sup 7}Be(d,p)2{alpha} reaction rate through the 5/2{sup +} 16.7-MeV state in {sup 9}B. The {sup 2}H({sup 7}Be,d){sup 7}Be reaction was used to search for such a resonance; none was observed. An upper limit on the width of the proposed resonance was deduced.

The most intense gamma-ray line observable from novae is likely to be from positron annihilation associated with the decay of 18F. The uncertainty in the destruction rate of this nucleus through the 18F(p,{\alpha})15O reaction presents a limit to interpretation of any future observed gamma-ray flux. Direct measurements of the cross section of both this reaction and the 18F(p,p)18F reaction have been performed between center of mass energies of 0.5 and 1.9 MeV. Simultaneous fits to both data sets with the R-Matrix formalism reveal several resonances, with the inferred parameters of populated states in 19Ne in general agreement with previous measurements. Of particular interest, extra strength has been observed above ECM \sim1.3 MeV in the 18F(p,p)18F reaction and between 1.3-1.7 MeV in the 18F(p,{\alpha})15O reaction. This is well described by a broad 1/2+ state, consistent with both a recent theoretical prediction and an inelastic scattering measurement. The astrophysical implications of a broad sub-threshold partner to this state are discussed., Comment: 7 pages, 4 figures, 2 tables

The level structure of 22Na has been studied at the Holifield Radioactive Ion Beam Facility in Oak Ridge National Laboratory using the 24Mg(p,3He)22Na reaction. 41 and 41.5 MeV proton beams were generated by 25 MV tandem accelerator and bombarded isotopically enriched 24Mg targets. Angular distributions of recoiling 3He particles were extracted by using a segmented annular silicon strip detector array. Spins and parities for ten levels were constrained through a distorted wave Born approximation analysis of angular distributions including three above the proton threshold at 6.739 MeV.

The 75As(d,pγ) reaction in inverse kinematics as a surrogate for neutron capture was performed at Oak Ridge National Laboratory using a deuterated plastic target. The intensity of the 165 keV γ-ray from 76As in coincidence with ejected protons, from exciting 76As above the neutron separation energy populating a compound state, was measured. A tight geometry of four segmented germanium clover γ-ray detectors together with eight ORRUBA-type silicon-strip charged-particle detectors was used to optimize geometric acceptance. The preliminary analysis of the 75As experiment, and the eïňČcacy and future plans of the (d,pγ) surrogate campaign in inverse kinematics, are discussed.

We directly measure the {sup 17}F(p,{gamma}){sup 18}Ne resonant reaction using a mixed beam of {sup 17}F and {sup 17}O at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory (ORNL). The astrophysically important 3{sup +} resonance at {approx}600 keV above the proton threshold in {sup 18}Ne is found to have a partial width {Gamma}{sub {gamma}} = 56 {+-} 24(stat) {+-} 30(sys) meV, in reasonable agreement with the theoretically predicted width. A 2{sigma} upper limit on the direct capture of S(E) = 65 keV b is determined at an energy of 800 keV. Experimental techniques and astrophysical implications are discussed.

There are a number of astrophysical environments in which the path of nucleosynthesis proceeds through proton-rich nuclei. These nuclei have traditionally not been available as beams, and thus proton-capture reactions on these nuclei could only be studied indirectly. At the Holifield Radioactive Ion Beam Facility (HRIBF), some of the first direct measurements of (p,\( \gamma\)) cross-sections on radioactive beams have been made. The Daresbury Recoil Separator (DRS) has been used to separate the recoils of interest from the unreacted primary beam and identify them in an isobutane-filled ionization counter. First data from 17F (p,\( \gamma\)18Ne and 7Be (p,\( \gamma\)8B measurements are presented.

The rate of the 17F(p,γ)18Ne reaction is of significant importance in astrophysical events like novae and x‐ray bursts. A 3+ state in 18Ne predicted to dominate the rate was found at 599.8 keV using the 17F(p,p)17F reaction [1], but the resonance strength was unknown. For the first time, the 17F(p,γ)18Ne reaction has been measured directly with the Daresbury Recoil Separator, using a mixed beam of radioactive 17F and stable 17O from the HRIBF at ORNL. A γ width was found for the 599.8 keV resonance in 18Ne, and an upper limit on the direct capture S factor was determined at an intermediate energy of 800 keV.

Direct reaction techniques are powerful tools to study the single-particle nature of nuclei. Performing direct reactions on short-lived nuclei requires radioactive ion beams produced either via fragmentation or the Isotope Separation OnLine (ISOL) method. Some of the most interesting regions to study with direct reactions are close to the magic numbers where changes in shell structure can be tracked. These changes can impact the final abundances of explosive nucleosynthesis. The structure of the chain of tin isotopes is strongly influenced by the Z=50 proton shell closure, as well as the neutron shell closures lying in the neutron-rich, N=82, and neutron-deficient, N=50, regions. Here we present two examples of direct reactions on exotic tin isotopes. The first uses a one-neutron transfer reaction and a low-energy reaccelerated ISOL beam to study states in 131Sn from across the N=82 shell closure. The second example utilizes a one-neutron knockout reaction on fragmentation beams of neutron-deficient 106,108Sn. In both cases, measurements of gamma rays in coincidence with charged particles proved to be invaluable., 11 pages, 5 figures, Zakopane Conference on Nuclear Physics "Extremes of the Nuclear Landscape", Zakopane, Poland, August 31 - September 7, 2014

A high-density supersonic gas-jet target named JENSA (Jet Experiments in Nuclear Structure and Astrophysics) has been constructed and commissioned at Oak Ridge National Laboratory. The target creates a localized (∼ 4 mm wide) thick (∼10 19 atoms/cm2) concentration of gaseous atoms (H, He, N, etc...) that are suitable for use in high-resolution experiments with radioactive beams. The interaction point of the beam with the gas-jet target is surrounded by silicon strip detectors from the SuperORRUBA (Oak Ridge Rutgers University Barrel Array) to detect reaction products with good energy (∼30 keV) and angular resolution (∼1 degree). Initial experiments are discussed along with plans for future use at Michigan State University.

Neutron capture reactions on unstable nuclei are important for both basic and applied nuclear science. A program has been developed at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory to study single-neutron transfer (d,p) reactions with rare isotope beams to provide information on neutron-induced reactions on unstable nuclei. Results from (d,p) studies on {sup 130,132}Sn, {sup 134}Te and {sup 75}As are discussed.

Studying ({alpha},p) reactions of astrophysical interest with radioactive beams presents serious challenges because of the difficult nature of the target. We have developed a new approach for the measurement of ({alpha},p) reactions using heavy ion beams in inverse kinematics and have measured the {sup 4}He({sup 19}F,{sup 1}H){sup 22}Ne reaction as a demonstration. {sup 19}F beams were used at the Holifield Radioactive Ion Beam Facility (HRIBF) tandem accelerator in Oak Ridge National Laboratory (ORNL) to bombard a large scattering chamber filled with {sup 4}He gas. Recoiling protons from the reactions were detected by the large area annular silicon strip detector array (SIDAR). The {sup 19}F({alpha},p) and {sup 19}F({alpha},p') excitation functions were measured over the energy range of E{sub c.m.} {approx} 1-2.1 MeV, demonstrating the viability of the technique