Coulomb dissociation reaction and correlations of two halo neutrons in 11Li

doi:10.1016/0370-2693(95)00131-4

Physics Letters B

Volume 348, Issues 1–2, 30 March 1995, Pages 29-34

https://doi.org/10.1016/0370-2693(95)00131-4 Get rights and content

Abstract

We have performed an exclusive measurement for the Coulomb dissociation reaction, $Pb(^{11} Li,^{9} Li+2n) X$ at an incident energy of 43 A MeV. The deduced excitation energy spectrum of the ¹¹Li nucleus shows a prominent peak at 1 MeV with a large tail towards higher excitation energies. The relative energy spectra for the n-n and ⁹Li−2n sub-systems show that the excitation is dominated by the relative motion between ⁹Li and the center-of-mass of the two neutrons. The above characteristics are explained by a direct Coulomb breakup mechanism with an extended ‘di-neutron’ model.

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Citation Excerpt :
From the theoretical point of view, the first model calculations for halo nuclei were made by the same authors of Ref. [51] using the sudden approximation and a method based on the Coulomb excitation theory of Adler and Winther [98]. A large number of publications exists dealing with either nuclear or Coulomb breakup [99–230]. For example theoretical models for the neutron angular distribution observable were introduced in [99,122] and [123].
The structure of exotic nuclei has only been studied from around 1985, because they are very short lived and because before that, it was not possible to produce and deliver them as beams on a target. They have large $N ∕ Z$ or $Z ∕ N$ ratios, are weakly bound and quite extended most of the time. Thus breakup, transfer and/or inelastic excitations of the surface are some of their most common reaction mechanisms. Direct reactions, for their simplicity, have played a fundamental role in the last thirty years in the process of understanding such “new” type of structures. On the other hand, direct reactions have been studied and understood for a much longer time, starting with the pioneering experiments in the early ’50 on deuteron-induced reactions and the reaction models developed by S.T. Butler and collaborators. Both subjects are extremely vast and there is a large literature available of books, review articles and original papers. I will discuss here only a few selected examples of the many interesting problems that have been encountered and solved in all those years. I consider them breakthroughs in the field and as such I hope they can inspire young generations of researchers.
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¹: Present address: RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-01, Japan.

²: Also RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-01, Japan.

³: Permanent address: KVI, University of Groningen, Zernikelaan 25, NL-9747 AA Groningen, The Netherlands.

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Physics Letters B

Abstract

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Neutron correlations in the decay of the first excited state of <sup>11</sup>Li