Scaling and interference in the dissociation of halo nuclei

Abstract

The dissociation of halo nuclei through their collision with light and heavy targets is considered within the Continuum Discretized Coupled Channels theory. We study the one-proton halo nucleus 8 B and the one-neutron halo nucleus 11 Be, as well as the more normal 7 Be. The procedure previously employed to extract the Coulomb dissociation cross section by subtracting the nuclear one is critically assessed, and the scaling law usually assumed for the target mass dependence of the nuclear breakup cross section is also tested. It is found that the nuclear breakup cross section for these very loosely bound nuclei does indeed behave as a + bA 1/3 . However, it does not have the geometrically inspired form of a circular ring which seems to be the case for normal nuclei such as 7 Be. We find further that we cannot ignore Coulomb-nuclear interference effects, which may be constructive or destructive in nature, and so the errors in previously extracted B(E1) using the subtraction procedure are almost certainly underestimated.

A study of proton breakup from exotic nuclei through various reaction mechanisms in 40A - 80AMeV energy range

“…The interference is so strong at low energy that it almost doubles the Table 1 one sees also that for both projectiles the total nuclear breakup cross sections are always of the same order of magnitude than the recoil Coulomb breakup on a heavy target but much smaller than the direct Coulomb and the total Coulomb cross sections. Thus we confirm what has already been suggested by other authors [5,10,11], on why in the past, calculated nuclear breakup of a proton has been found comparable to or even larger than the Coulomb breakup. The misinterpretation was simply due to an underestimate of the direct Coulomb breakup due to both the dipole approximation and its treatment to first order and to the fact that interference effects were overlooked.…”

Coulomb and Nuclear Breakup at Low Energies: Scaling Laws

“…What is first done (wrongly) is to ignore σ bu inter f erence , and consider σ bu N to scale linearly with the mass number of the target nucleus. We rely on a recent study of this topic, especially with regards to the dependence on the target mass, made at higher energies, [3,4]. According to this study, the nuclear breakup cross section behaves at a given value of the bombarding energy, E Lab as,…”

“…According to this study, the nuclear breakup cross section behaves at a given value of the bombarding energy, E Lab as, In the above P 1 and P 2 , given in mb, are functions of the bombarding energy, and structure of the projectile. This formula, well substantiated by extensive continuum discretized coupled channels calculation in [3], is used to estimate the nuclear cross section for breakup on a heavy target, given the experimental value of the cross section on a light target such as 12 C, where the Coulomb breakup is usually much smaller. We mention here that [5] also derive a scaling law, but finds a different dependence on the target mass.…”

“…For the heavy target case, the interest resides in exactly the Coulomb breakup, through which the dipole response can be extracted. In the procedure the interference between the nuclear and Coulomb contributions is ignored which is not always justified [3]. As mentioned above, the next step used by practitioners is to measure the breakup of, say, 11 Be on a 12 C target and assume it is predominantly nuclear, then extrapolate to the heavy targets such as the case of nuclear breakup contribution to 11 Be + 208 Pb [8? ]…”

“…Of course the above procedure is faulty as the interference term could be important, as demonstrated in [3,6].…”