Session DB: Mini-Symposium on Experimental Advances in Transfer Reactions II

Thursday, October 27, 2011

Nuclei far from stability have opened new avenues for constructing a more complete view of nuclei. The emergence of exotic forms of nuclei such as halo and skin together with the associated changes in shell structure have raised great interest towards understanding the underlying reasons. Nucleon transfer reactions and inelastic scattering using ISOL beams are greatly extending our understanding on structure of exotic, complementing the information gathered from reactions using projectile-fragmentation beams. The presentation will discuss experiments using re-accelerated beams at ISAC, TRIUMF investigating halo features and evolution of shell structure in light neutron-rich nuclei. A brief overview of the related experimental facilities will also be presented with a future outlook. Work done with the ISAC Direct Nuclear Reactions Collaboration.   

Thursday, October 27, 2011

The dispersive optical model is applied to transfer reactions. A systematic study of (d,p) reactions on closed shell nuclei using the finite-range adiabatic reaction model is performed at several beam energies and results are compared to data as well as to the results from using the global optical potential CH89. Overall, the dispersive optical model is able to describe the angular distributions as well or better than the CH89 parametrization. In particular, the dispersive optical-model provides a much better extrapolation for the (d,p) reaction on $^{132}$Sn. Since the dispersive optical-model incorporates negative energies, it also constrains the overlap function. Spectroscopic factors extracted using the dispersive optical-model are generally lower than those using standard parameters, and more in line with results obtained from (e,e'p) measurements.   

Thursday, October 27, 2011

The partial widths of states near threshold are crucial to characterize the rates of thermonuclear capture reactions. Direct measurements are often difficult, because cross sections are small. We have studied the $^{17}$O(d,p)$^{18}$O and $^{14} $C($^6$Li,d)$^{18}$O reactions in inverse kinematics to populate excited states near and above the n- and $\alpha$- thresholds in $^{18}$O using the HELIOS spectrometer at ANL. HELIOS was essential to obtain the Q-value resolution necessary to separate the individual excited states, as well as to provide high coincidence efficiency for determining the specific decay modes. The branching ratios ($\Gamma_{\alpha}/ \Gamma_{\gamma}$ and $\Gamma_{n}/\Gamma_{\gamma}$) will be presented and compared to the other experiments. Results from the $\alpha$-transfer reaction of $^{6}$Li($^{14}$C,d) using HELIOS will also be discussed.   

Thursday, October 27, 2011

The structure of the proton-rich nucleus $^{9}$C is poorly known. Only a few excited states have been observed and little information exists on their single-particle characteristics. The measured magnetic dipole moment is anomalously high and could suggest higher order configurations in the ground state wave function. The $^{10}$C(d,t)$^{9}$C reaction, in inverse kinematics, was used to populate states in $^{9}$C. The radioactive $^{10}$C beam was produced at the ATLAS In-flight facility through the p($^{10}$B,$^{10}$C)n reactions using a 185 MeV $^{10}$B beam incident on a cryogenic H$_{2}$ gas cell. The intensity of the secondary beam (E=171 MeV) was about 4x10$^{4}$ pps. The beam was incident on a 650 $\mu$g/cm$^{2}$ deuterated polyethylene (CD$_{2}$) target. Tritons were detected in a series of annular double sided silicon detectors covering $\theta$$_{lab}$ between 12 and 42 degrees. The heavy recoils were detected in a set of forward-angle silicon detectors in a $\Delta$E-E configuration. Preliminary results will be presented. Work was supported by the U. S. Department of Energy, Office of Nuclear Physics, under Contracts DE-FG02-04ER41320 and DE-AC02-06CH11357.   

Thursday, October 27, 2011

The exact shell-structure of the unstable doubly-magic nucleus $^{56}$Ni has attracted a lot of interest recently. To test if $^{56}$Ni is a good core, $^{56}$Ni(p, d)$^{55}$Ni transfer reactions were measured using $^{56}$Ni beam at two different energies, 37 MeV/u and 80 MeV/u, in inverse kinematics in two experiments. The second measurement was done in order to test the sensitivity of reaction cross sections and models to reaction energies. The measurements were performed at NSCL using HiRA array and S800 spectrometer. Spectroscopic factors have been extracted for the first experiment. The results show good agreement with shell-model calculations. Preliminary results of the measurements with 80 MeV/u beam will be presented as well.   

Thursday, October 27, 2011

The $^{84}$Se(p,d)$^{83}$Se and $^{86}$Kr(p,d)$^{85}$Kr reactions at 45 MeV/u in inverse kinematics were measured at the National Superconducting Cyclotron Laboratory, using the charged particle detector HiRA and the S800 spectrometer. This experiment is the first to use the full complement of 20 HiRA telescopes. The primary goal is to extract angular momentum quantum numbers and neutron spectroscopic factors for the ground and first excited states of $^{83}$Se. Details of the experiment and a status report on the data analysis will be discussed.   

Thursday, October 27, 2011

Nuclei with a few nucleons above and below shell closures are of particular importance to informing the evolution of single-particle structure, which is critical to the benchmarking of nuclear models. Due to increasingly intense beams of radioactive nuclei, studies around the doubly-magic $^{132}$Sn shell closure are now possible. While the single-neutron states in tin nuclei in immediate proximity to the N=82 shell gap have recently been verified to be highly pure, fragmentation of the single-neutron strengths in the tellurium isotopes has been observed. The nature of this fragmentation provides a stringent test of shell model effective interactions. In order to study the fragmentation in nuclei close to the N=82 shell gap, a series of (d,p) measurements is being undertaken at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory, utilizing the superORRUBA silicon detector array. Motivation, experimental details and preliminary data will be presented. Work supported in part by U.S. Department of Energy and National Science Foundation.   

Thursday, October 27, 2011

Measurements of angular distributions for one and two proton stripping reactions for $^{28}$Si+$^{90,94}$Zr systems were performed at lab energy 120 MeV with $^{28}$Si beam at Inter University Accelerator Center, New Delhi. Theoretical calculations performed using the quantum mechanical coupled reaction channels code FRESCO (including various intermediate states involving target and projectile excitations before and/or after transfer along with sequential transfer) were able to reproduce one and two proton transfer angular distributions for both the systems reasonably well. It was found that the DWBA calculations could describe the one proton transfer data well for both the systems but failed to reproduce the angular distributions for two proton transfer channels. The present measurements underline the importance of sequential transfer at energies much above the Coulomb barrier. We had also performed transfer reaction measurements for these systems in the sub- and near barrier region using recoil mass separator.