ISSN 1063-7788, Physics of Atomic Nuclei, 2007, Vol. 70, No. 12, pp. 2079–2085. c  Pleiades Publishing, Ltd., 2007. NUCLEI Theory Comparison of Halo of 11 Be, 15 C, and 19 C * R. Kharab ** , R. Kumar, P. Singh, and H. C. Sharma 1) Department of Physics, Kurukshetra University, India Received November 24, 2006; in final form, February 28, 2007 Abstract—We have compared the halo of 11 Be, 15 C, and 19 C nuclei by analyzing the one-neutron stripping reaction data on the Be target at 60-, 54-, and 57-MeV/A beam energies, respectively, within the frame- work of the eikonal approximation approach. The determination of effective range through the comparison of the total cross section data and prediction has revealed that the halo of 19 C is the well developed, while that of 15 C is the least and that of 11 Be lies in between these two. The longitudinal momentum distribution data also strengthen these observations. PACS numbers: 25.60.Gc, 25.70.Mn, 25.60.Dz DOI: 10.1134/S1063778807120095 1. INTRODUCTION Following the pioneering work of Tanihata et al. [1], the breakup reactions of unstable nuclei lying in the close vicinity of the neutron/proton drip line have confirmed the existence of a novel nuclear structure frequently refered to as nucleon halo. This peculiar nuclear structure consists of a nuclear core with nor- mal nuclear density and one or two diffused valence nucleon(s). This threshold effect may be attributed to the tunneling out of the outermost valence nucleon(s) to the classically forbidden region. An unexpectedly large matter radius, long tail in density distribution, small binding energy, and narrow longitudinal mo- mentum distribution (LMD) of the constituent frag- ments in their ground state are some of the charac- teristic features of the halo nuclei. Because of these unique ground-state properties of halo nuclei, their breakup cross section on a light or heavy target has been found to be significantly enhanced. In case of light target and at small impact parame- ter, the breakup occurs predominantly by the nuclear interaction between the participants through two dif- ferent mechanisms, namely, stripping and diffraction dissociation. In the stripping reaction, one of the con- stituent fragments of the projectile is absorbed by the target, while the other goes out [2]. The stripping reaction involving halo nuclei represents an efficient tool to ascertain various ground-state properties of ∗ The text was submitted by the authors in English. 1) Department of Applied Sciences, Haryana College of Tech- nology and Management, Kaithal, India. ** E-mail: kharabrajesh@rediffmail.com these nuclei [3]. So far, a number of different theo- retical models have been proposed to deal with the stripping reactions of halo nuclei [2, 4–7]. However, at high energies, the eikonal approximation approach has been considered the most convenient [8]. Experimentally, one-neutron ( 11 Be, 19 C) [9, 10], one-proton ( 8 B) [11], and two-neutron ( 11 Li) [12] halo structures have been well established. However, the nuclei with one valence neutron occupying the l = 0 orbital have attracted significant attention. Besides being simple, the absence of centrifugal and Coulomb barriers strengthens their candidature for halo struc- ture. Some of the light neutron-rich nuclei like 11 Be and 19 C appear to have well-developed one-neutron halo structure, while 15 C is good candidate for it. In the present work, we have compared the halos of these nuclei by determining the effective range of the nuclear interaction between the valence neutron and core through comparison of experimental and theoretical stripping cross sections. The theoretical formalism is described briefly in Section 2, while the results are discussed in Section 3. The conclusions are presented in Section 4. 2. THEORETICAL FORMALISM The basic expression for the neutron absorption cross section, differential in the momentum of the core (k c ) within the eikonal approximation approach, is given by [7] dσ dk c = 1 (2π) 3 1 2L 0 +1 (1) ×  M 0  d 2 b n [1 −|S n (b n )| 2 ] 2079