NUCLEAR PHYSICS A Nuclear Physics A616 (1997) 223~230~ Quasifree Nucleon-knockout Reactions from Neutron-rich Nuclei by a Proton Target: p(eHe,pn)sHe, p(“Li,pn)loLi, p(6He,2p)sH, and p(“Li,2p)lOH e T. Kobayashit, K. Yoshidal, A. Ozawat, I. Tanihatat, A. KorsheninnikovtX*, E. Nikolsk?. and T. Nakamura3 1 RIKEN, 2-l Hirosawa, W ako, Saitama 351-01, Japan 2 The Kurchatov institute, Kurchatov sq. 1, Moscow 123182, Russia 3 University of Tokyo, 7-3-l Hongo, Bunkyo-ku, Tokyo 113, Japan Abstract Quasifree neutron-knockout (p,pn) reactions by a proton target from neutron- rich nuclei, “Li (6He), were used to study the structure of l”Li (5He) and the momentum distribution of halo neutrons. Quasifree proton-knockout (p,2p) reactions from 11Li (6He) projectiles to loHe (5H) resonances were also observed. 1. Introduction Light exotic nuclei, such as 6He and 1 lLi, are known to have an extended neutron distribution, called a neutron halo or skin [ 11. One interesting feature of such nuclei is that the system is composed of two valence neutrons and the core, and that any 2 sub-systems are unbound. For understanding such nuclei, one key point is the single-particle properties of the valence neutrons, which are generally difficult to be studied. In this paper, we report on quasifree nucleon-knockout reactions from such nuclei by a proton target for studying the single-particle properties of valence neutrons in 6He and IlLi. Quasifree nucleon-knockout reactions, (p,2p) and (e,e’p), by high-energy proton or electron beams have been used to study the single-particle properties, such as the binding energy or the momentum distribution, of bound nucleons inside the nucleus [2]. In the (p,2p) reaction, the 4-momenta of two protons from quasifree nucleon-nucleon scattering are measured. The momentum (q ) of the removed proton in the nucleus is expressed as 4 = Pl + P2 - PO where pl, p2. and po are the momenta of the scattered protons and the incident proton, respectively. Information concerning the orbital angular momentum can be extracted from the observed momentum distribution. The separation energy (E,) of the removed proton, defined as MA-~ + MP - MA, is expressed as E,=To-T,-T2-L 2MA-l 037S-9474/97/%17.00 0 1997 - Elsevier Science B.V. All rights reserved. PI’: SO37S-9474(97)00092-4