Proton Elastic Scattering on Neutron Halo Nuclei

Abstract

Elastic scattering of protons from 6Li and 6He is studied in the intermediate-energy region (EP 3 100 MeV) in a folding model with .realistic. target densities which reproduces the r.m.s. radii and a range of electroweak data. The scattering clearly reflects the size of the systems, but is only marginally able to discriminate between details of the correlated valence structures of the two nuclei: at forward angles, where the direct fingerprint of the presence of a halo structure is expected, the cross-section differences are small; at large angles, where the response of the .*-core on the halo structure is probed, the differences found are accompanied by a falling cross-section magnitude. Likewise, only a weak dependence is found to differences in the halo tail, corresponding to three calculations for "Li which all reproduce the experimental r.m.s. radius.

Sensitivities of the proton-nucleus elastic scattering observables of6Heand8Heat

“…The one model with the most significant differences in shape is again the BS model (and only at higher angles). This model has the tightest core, and a loose valence wave function, as it had for 6 He. There is nothing that can be learned about the valance structure of 8 He from studying this reaction's differential cross section for the data which exist.…”

“…The mode of construction of 8 He is also in contradiction with most other structure calculations for 8 He. To first order, 6 He could be approximated as a 4 He + 2n; however, it is apparent that 8 He is closer to 4 He+4n than ( 4 He +2n) +2n as the BS model would suggest [20]. The second model is a relativistic point coupling model within the framework of a chiral effective field theory by Rusnak and Furnstahl [27].…”

“…Most varieties of the chiral effective theory reproduce the bulk nuclear observables of spherically symmetric nuclei. Questions of applicability to exotic helium nuclei can of course be raised while using this model, for it was not developed for the non-spherical, non-bulk nuclei 6 He and 8 He. The numerical procedure to create the off-shell densities (Eq.…”

“…The last nuclear model to be discussed was developed explicitly for exotic nuclei. The COSMA model (cluster orbit shell model approximation) [20,21], an approximation to the three body problem, has been used extensively in the literature to describe elastic scattering with the exotic helium nuclei [4,6,7,11,12,36,40]. The COSMA model is a combination of nucleon clustering and the standard shell model, which obeys the Pauli exclusion principle by using Slater determinants to produce a fully antisymmetrized wave function in r-space.…”

“…Simply if S d > 0 then we define this nucleus as having a halo because there is a well defined separation between the core and halo centers. The only discernible halo nucleus is the COSMA model of 6 He. It contains a tightly bounded core wave function with adequate spacing between core and valence nucleons.…”