Single Cooper pair transfer in stable and in exotic nuclei

Abstract

renormalized by medium polarization effects (structure), also meant the end of superconductivity as a wide open, speculative field and the beginning of a thoroughly quantitative "exact" era, with uncertainties below the 10% level.From this vantage point of view it is not difficult to argue that important progress in the understanding of pairing in atomic nuclei will arise from a systematic, quantitative study of two-particle transfer reactions on drip line, exotic, halo nuclei (like for example 11 Li), stabilized by the pairing correlations associated with a single Cooper pair, as well as on many (but still few)-Cooper pair systems like e.g. the Sn-isotopes, setting equal emphasis on the structure as well as on the reaction aspects of the process. Time seems ripe for such a study, in keeping with the fact that one now knows how to correlate pairs of nucleons taking properly into account the interplay between bare and medium polarization (induced) nuclear pairing interactions. Also how to calculate the absolute value of the twoparticle transfer cross sections taking properly into account the full non-locality of the Cooper pairs, as well as the multistep (successive, simultaneous and nonorthogonality) contributions to it. The above expectation is strongly supported by the results emerging from the analysis of a broad sample of two-nucleon transfer data.In particular, from the analysis of recent data from (p, t) reactions on 11 Li and Sn-isotopes, carried out making use of a unified nuclear field theoretical description of structure and reaction mechanisms, which testify to the fact that theory is now able to provide an overall account of the experimental findings, in particular of the absolute two-particle transfer cross section, within experimental errors and without adjusting any free parameter. This is also true when the multistep theory of two-particle transfer together with detailed, microscopic, nuclear structure wavefunctions is applied to (t, p) and ( 16 O, 18 O) data associated with the 206 Pb(gs) 208 Pb(gs) processes.

Surface-enhanced pair transfer amplitude in quadrupole states of neutron-rich Sn isotopes

“…Our study is based on the Skyrme-Hartree-Fock-Bogoliubov mean-field theory in describing the pair correlated ground state, and the quasiparticle random phase approximation (QRPA) [48] (and references in [50]) to describe the 2 + states and the associated pair transfer modes. In the present work, we concentrate on the nuclear structure aspects, and leave the cross section and the reaction mechanism of the neutron pair transfer [31,[51][52][53] for future works. The formalism is described in Section 2.…”

More is different: 50 years of nuclear BCS

“…Examples of such a program are collected in Table 1. From these results, as well as many detailed controls 37 , it seems fair to summarize the present situation concerning the probing of single-and multi-Cooper pair nuclei with the help of two-nucleon transfer reactions as written in the conclusions.…”

“…Absolute two-particle transfer cross sections are to be calculated for a quantitatively accurate comparison between theoretical and experimental studies of nuclear pairing. This is possible by treating on equal footing, for example within the framework of NFT, both structure and reactions (see [8][9][10][11][12][13] and; 26,27,33,37 see also the contribution of Thompson to the present Volume), and making use of global sets of optical parameters. No details are given in the present contribution as to the methods, routines and theoretical details entering the calculations, as they have been extensively reported in the literature quoted above (see also the contribution of Potel and Broglia to this Volume).…”

Nuclear field theory predictions for 11Li and 12Be: Shedding light on the origin of pairing in nuclei

“…This result, together with the fact that ∆/U (r ≈ R 0 ) ≈ 4 × 10 −2 , U (r) being the average mean field potential, implies, as a rule, that successive transfer, where U acts twice, is dominant as compared to the simultaneous transfer of two nucleons, a process in which U acts once, the second nucleon being transferred partially making use of the interaction energy between the partners of the Cooper pair, and partially exploiting the non-orthogonality of the singleparticle wavefunctions associated with the mean field of target and projectile. It is of notice that this argumentation is at the basis of one of the cornerstones of superconductivity in metals, namely the Josephson effect [21,22] (see also [23] and references therein).…”