Interplay of static and dynamic effects inHe6+U238fusion

Abstract

We investigate the influence of the neutron halo and the breakup channel on the total 6 He+ 238 U fusion cross section at near-barrier energies. To include static effects of the 2n-halo in 6 He nuclei, we use a single-folding potential obtained from an appropriate nucleon-238 U interaction and a realistic 6 He density. Dynamical effects arising from the breakup process are then included through coupled-channel calculations. These calculations suggest that static effects dominate the cross section at energies above the Coulomb barrier, while the coupling to the breakup channel is more important at sub-barrier energies. The comparison of our calculations with recent data suggests that the coupling to other channels may be influencing the cross section at very low energies.

Schematic coupled-channel calculations for nuclear reactions with unstable beams

“…[26] to investigate the importance of static and dynamic effects of the 6 He halo in collisions with heavy targets. In this model, the two neutrons in the 6 He halo are treated as a single particle, the dineutron, and the breakup channel is approximated by a single effective state.…”

“…Further details of this procedure are given in ref. [26]. Since the nuclear form factor for the 6 He+ 209 Bi system should be very similar to that for 6 He+ 238 U, we use the same nuclear form factors in both calculations.…”

“…To avoid this problem we follow the procedure introduced in ref. [26], which is described below. The nuclear part of the coupling interaction, V, is obtained by summing the interaction between the 4 He fragment and the target (V4 He ) with that between the dineutron and the target (V 2n ) and subtracting the projectiletarget potential, V N (r).…”

“…The total fusion cross sections measured in the 38 From the above discussion, it is clear that further theoretical and experimental studies are needed for an appropriate understanding of the nuclear reactions induced by unstable beams. In the present paper we use a simple approximation for the breakup channel proposed in a previous paper [26] to carry out coupled-channel calculations for fusion, breakup, reaction and elastic cross sections. In particular, we calculate the fusion cross sections for the 4,6 He + 238 U and 4,6 He + 209 Bi systems, which have recently been measured [22,21].…”

Assessing the adequacy of the bare optical potential in near-barrier fusion calculation

“…radius corresponding to that of 4 He scaled by the factor (6/4) 1/3 , as in Ref. [15]. The two densities are compared in Fig.…”