Proton spectroscopic factor of the12Cground state from the12C(11B<

Abstract

The angular distributions of the i2C ("B , " B ) 12C and 12C(n B, 12C)n B reactions have been measured at an incident energy of 50 MeV by using the high resolution Q3D magnetic spectrometer of the HI-13 tandem accelerator at China Institute of Atomic Energy, Beijing. The optical potential parameters of the 11B + l2C system are determined by fitting the angular distribution of the elastic scattering and then used to predict the cross sections of the elastic transfer reaction leading to the ground state in l2C based on distorted-wave Born approximation (DWBA) analysis. Taking into account the interference between the elastic scattering and the elastic transfer processes, the proton spectroscopic factor of the 12C ground state is extracted to be 2.15 ± 0.23 by constraining the geometrical parameters r0 and a using the rms radius of the valence proton in the l2C ground state.The essential constituents of nuclear shell model are the single-particle orbits of the mean field which are occupied by protons and neutrons under the Pauli principle [1]. The spectroscopic factor is defined by a matrix element which describes the overlap between the initial and final states and yields the information on the occupancy of a given single particle orbit [2], It provides quantitative information about the single-particle structure of nuclei and plays an important role in a variety of topics on nuclear reaction and nuclear astrophysics.The proton spectroscopic factor of the 12C ground state is of special interest since it can be used in the calculation of the astrophysical n B(/>, y ) 12C rate [3]. Shell model calculations done by Cohen-Kurath [4] in 1967 predicted the proton spectroscopic factor of the ,2C ground state to be Si2C = 2.85. After that, several experiments were performed through nC(e,e'p)"B [5], n C(p,2p)"B [6], uB(d,n)nC [7], 12C(<7,3H e)n B [8,9], u B(3H e,t/)12C [10,11], n B(7L i,6H e)12C [12], and l2C (n B, 12C )n B [13,14] reactions. The spectro scopic factors extracted from these measurements are different from each other in the range of 1.85 and 4.1.Generally speaking, the elastic transfer reaction is regarded as a good tool for extracting spectroscopic factors since the spectroscopic factors as well as the distorted scattered waves are identical in both entrance and exit channels. Thus, the elastic transfer reaction enables the reduction of the uncertainty of the spectroscopic factor and has been frequently used to determine the neutron spectroscopic factor of 7Li [15]; the *zhli@ciae.ac.cn proton spectroscopic factors of 9Be [16], 10B [17], ,4N [17], and lbO [17]; the 3He spectroscopic factor of 12C [18]; and the 4He spectroscopic factors of 7Li [19] and 13C[18].For the 12C ("B , 12C )n B elastic transfer reaction, the angu lar distributions have been well reproduced by the distortedwave Born approximation (DWBA) theory. However, there is still a remarkable discrepancy in the proton spectroscopic factor of the 12C ground state [14], It shows a smooth change with energy, and even exceeds the theoretical limit of...