Survey of neutron spectroscopic factors and asymmetry dependence of neutron correlations in transfer reactions

Transfer reactions have been used as an experimental tool to obtain abundant spectroscopic information for stable nuclei in the past half-century. With the advance of high intensity radioactive beams, transfer reactions can be used in the same spirit to explore the structures of exotic nuclei, where dramatic changes in nuclear structure have been observed near the drip lines.;This thesis work is partly motivated by the revived interest in transfer reactions using rare isotope beams. The first part of this dissertation describes the survey of spectroscopic factors extracted from an extensive amount of data on single neutron (p,d) and (d,p) transfer reactions on stable isotopes from Lithium to Nickel. Utilizing the global optical model potential, Chapel-Hill 89, and the conventional single-particle geometry in the adiabatic distorted wave approximation (ADWA) model, the measured ground-state and most excited-state neutron spectroscopic factors for nuclei with 3 ≤ Z ≤ 28 agree with the predictions from large-basis-shell-model to better than 30%. The established systematics provides an essential framework to analyze the structural information obtained from transfer reactions for both stable and exotic nuclei. The suppression of spectroscopic factors from shell model values due to nucleon-nucleon correlations is explored by using different optical model parameters and single nucleon bound state geometry. For most nuclei, the neutron ground-state spectroscopic factors are reduced by about 30% compared to large-basis-shell-model predictions if the ADWA reaction model uses transferred-neutron bound state and microscopic Jeukenne, Lejeune and Mahaux (JLM) nucleon-target optical potential geometries constrained by Hartree-Fock calculations. The magnitude of reduction is similar to that obtained in (e,e'p) measurements near the closed shells.;The neutron-proton asymmetry dependence of the reduction in the spectroscopic factor is related to the neutron-neutron and neutron-proton correlations. The experimental efforts in this dissertation are dedicated to the study of the asymmetry dependence of neutron correlations through spectroscopic factor measurements using (p,d) neutron transfer reactions with proton-rich 34Ar and neutron-rich 46Ar radioactive beams in inverse kinematics. The kinematically complete experiments use a high resolution silicon strip array to detect the deuterons in coincidence with the recoil residues detected in a mass spectrometer. The experimental results show little reduction of the ground-state neutron spectroscopic factor of the proton-rich nucleus 34Ar compared to that of neutron-rich 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region. The results are consistent with the systematics established from the extensive studies of spectroscopic factors from transfer reactions. They are, however, contradictory to the strong dependence obtained in knockout reactions. Our new results pose intriguing questions about the reaction mechanisms of transfer and knockout reactions as well as the nature of neutron correlations in nuclei with extreme isospin asymmetry.