Refractive effects in the scattering of loosely bound nuclei

Abstract

A study of the interaction of the loosely bound nuclei 6,7 Li at 9 and 19 MeV/ nucleon with light targets has been undertaken. With the determination of unambiguous optical potentials in mind, elastic data for four projectile-target combinations and one neutron transfer reaction 13 C͑ 7 Li, 8 Li͒ 12 C have been measured over a large angular range. The kinematical regime encompasses a region where the mean field (optical potential) has a marked variation with mass and energy, but turns out to be sufficiently surface transparent to allow strong refractive effects to be manifested in elastic scattering data at intermediate angles. The identified exotic feature, a "plateau" in the angular distributions at intermediate angles, is fully confirmed in four reaction channels and is interpreted as a prerainbow oscillation resulting from the interference of the barrier and internal barrier far-side scattering subamplitudes.

Elastic scattering of the proton drip-line nucleusF17

“…The internal component (triangles) has nonvanishing values up to grazing angular momentum and is completely negligible beyond this value. The average value for l l g is |S I | ≈ 10 −3 , 2 orders of magnitude fewer than for 6 Li+ 12 C at 9 MeV/ nucleon [4].…”

“…The corresponding total scattering amplitude is decomposed likewise as f WKB = f B + f I and the angular distributions as σ B(I ) = |f B(I ) | 2 by use of the usual angular momentum expansion of the amplitudes. The B(I ) components are calculated from classical action integrals along complex paths between turning points; see [4,31] for details. We take as an example 17 F+ 14 N and the potential "A" in Table III.…”

“…In this work we test this description of optical-model potentials for the more loosely bound sd-shell nucleus 17 F. We measured elastic-scattering angular distributions for the 14 N( 17 F, 17 F) 14 N and 12 C( 17 F, 17 F) 12 C reactions at 10 MeV/nucleon. This energy is about half of the saturation energy for light nuclei (the energy at which almost all reaction channels are open), and there are indications that traces of an increased transparency in the optical potential could be revealed [4].…”

“…Previous studies of scattering of p-shell nuclei showed that a doublefolding procedure with a modified version of the nuclear matter approach of Jeukenne, Lejeune, and Mahaux (JLM) [5] provided a good description of potentials for loosely bound nuclei by use of the normal absorptive component of the JLM nucleon-nucleon interaction. However, the real part of the potential required significant renormalization to account for effects of the DPP [4,6]. In this work we test this description of optical-model potentials for the more loosely bound sd-shell nucleus 17 F. We measured elastic-scattering angular distributions for the 14 N( 17 F, 17 F) 14 N and 12 C( 17 F, 17 F) 12 C reactions at 10 MeV/nucleon.…”

“…Long tails (or halos) may appear in the singleparticle densities, and the total reaction and one-particleremoval cross sections are large. The enhanced density in the tail leads to a competition between the enhanced refractive power of the real potential and the increased absorption that is due to the long-range part of the effective nucleon-nucleon interaction that results sometimes in exotic elastic-scattering angular distributions [4]. The coupling of the elastic channel with breakup and nucleon-transfer channels leads to a dynamic polarization potential (DPP) that is complex and nonlocal, with a complicated mass, energy, and radial dependence.…”