[en] Capture-fission cross sections were measured for the collision of the massive nucleus ¹³²Sn with ⁹⁶Zr at center-of-mass energies ranging from 192.8 to 249.6 MeV in an attempt to study fusion enhancement and hindrance in this reaction involving very neutron-rich nuclei. Coincident fission fragments were detected using silicon detectors. Using angle and energy conditions, deep inelastic scattering events were separated from fission events. Coupled-channels calculations can describe the data if the surface diffuseness parameter, a, is allowed to be 1.10 fm instead of the customary 0.6 fm. The measured capture-fission cross sections agree moderately well with model calculations using the dinuclear system model. If we use this model to predict fusion barrier heights for these reactions, we find the predicted fusion hindrance, as represented by the extra push energy, is greater for the more neutron-rich system, lessening the advantage of the lower interaction barriers with neutron-rich projectiles

[en] The ¹⁸Ne(α,p)²¹Na reaction plays a crucial role in the (α,p) process, which leads to the rapid proton capture process in x-ray bursts. The reaction rate depends upon properties of ²²Mg levels above the α threshold at 8.14 MeV. Despite recent studies of these levels, only the excitation energies are known for most with no constraints on the spins. We have studied the ²⁴Mg(p,t)²²Mg reaction at the Oak Ridge National Laboratory (ORNL) Holifield Radioactive Ion Beam Facility (HRIBF), and by measuring the angular distributions of outgoing tritons, we provide some of the first experimental constraints on the spins of astrophysically important ¹⁸Ne(α,p)²¹Na resonances

[en] The ¹⁸Ne(α,p)²¹Na reaction plays a crucial role in the (α,p) process, which leads to the rapid proton capture process in X-ray bursts. The reaction rate depends upon properties of ²²Mg levels above the α threshold at 8.14 MeV. Despite recent studies of these levels, only the excitation energies are known for most with no constraints on the spins. We have studied the ²⁴Mg(p,t)²²Mg reaction at the Oak Ridge National Laboratory (ORNL) Holifield Radioactive Ion Beam Facility (HRIBF), and by measuring the angular distributions of outgoing tritons, we provide the first experimental constraints on the spins of astrophysically-important ¹⁸Ne(α,p)²¹Na resonances

[en] As hindrance sets in for the fusion of heavier systems, the effect of large neutron excess in the colliding nuclei on their probability to fuse is still an open question. The detection of evaporation residues (ERs), however, provides indisputable evidence for the fusion (complete and incomplete) in the reaction. We therefore devised a system with which we could measure ERs using low intensity neutron-rich radioactive ion beams with an efficiency close to 100%. We report on measurements of the production of ERs in collisions of ^132,134Sn, ¹³⁴Te and ¹³⁴Sb ion beams with medium mass, neutron-rich targets. The data taken with ^132,134Sn bombarding a ⁶⁴Ni target are compared to available data (ERs and fusion) taken with stable Sn isotopes. Preliminary data on the fusion of ¹³²Sn with ⁹⁶Zr target are also presented

[en] Calculations of r-process nucleosynthesis rely significantly on nuclear structure models as input, which are not well tested in the neutron-rich regime, due to the paucity of experimental data on the majority of these nuclei. High quality radioactive beams have recently made possible the measurement of (d,p) reactions on unstable nuclei in inverse kinematics, which can yield information on the development of single-neutron structure away from stability in close proximity to suggested r-process paths. The Oak Ridge Rutgers University Barrel Array (ORRUBA) has been developed for the measurement of such reactions. An early partial implementation of ORRUBA has been utilized to measure the ¹³²Sn(d,p)¹³³Sn and ¹³⁴Te(d,p)¹³⁵Te reactions for the first time

[en] Recent calculations suggest that, at late times in the r-process, the rate of neutron capture by ¹³⁰Sn has a significant impact on nucleosynthesis. Direct capture into low-lying bound states is likely the dominant reaction in the r-process near the N=82 closed shell, so reaction rates are strongly impacted by the properties of neutron single particle states in this region. In order to investigate these properties, we have acquired (d,p) reaction data in the A∼132 region in inverse kinematics using ∼630 MeV beams (4.85 MeV/u for ¹³⁰Sn) and CD₂ targets. An array of Si strip detectors, including SIDAR and an early implementation of the new Oak Ridge Rutgers University Barrel Array (ORRUBA), was used to detect reaction products. Preliminary results for the ¹³⁰Sn(d,p)¹³¹Sn experiment are reported

[en] 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 ^130,132Sn, ¹³⁴Te and ⁷⁵As are discussed