The magic nature of 132Sn explored through the single-particle states of 133Sn

Abstract

Atomic nuclei have a shell structure in which nuclei with 'magic numbers' of neutrons and protons are analogous to the noble gases in atomic physics. Only ten nuclei with the standard magic numbers of both neutrons and protons have so far been observed. The nuclear shell model is founded on the precept that neutrons and protons can move as independent particles in orbitals with discrete quantum numbers, subject to a mean field generated by all the other nucleons. Knowledge of the properties of single-particle states outside nuclear shell closures in exotic nuclei is important for a fundamental understanding of nuclear structure and nucleosynthesis (for example the r-process, which is responsible for the production of about half of the heavy elements). However, as a result of their short lifetimes, there is a paucity of knowledge about the nature of single-particle states outside exotic doubly magic nuclei. Here we measure the single-particle character of the levels in (133)Sn that lie outside the double shell closure present at the short-lived nucleus (132)Sn. We use an inverse kinematics technique that involves the transfer of a single nucleon to the nucleus. The purity of the measured single-particle states clearly illustrates the magic nature of (132)Sn.

Evolution of single-particle states beyond132Sn

“…As already mentioned in the Introduction, the singleneutron nature of the observed states in 133 Sn has been recently studied in a (d,p) transfer reaction with a 132 Sn RIB [4,5]. In this experiment, the spectroscopic factors of the previously observed [18] 7/2 − , 3/2 − , and 5/2 − states were extracted evidencing a little fragmentation of the single-particle strength.…”

“…This is for instance the case of the 132 Sn(d,p) reaction recently performed at the first-generation RIB facility at Oak Ridge National Laboratory [4,5]. This experiment allowed to investigate the single-particle structure of the one-valence neutron nucleus 133 Sn, and the spectroscopic factors for the ground and three excited states extracted from the differential cross sections turned out to be very close to one.…”

Medium-spin states in neutron-rich83As and81As

“…As for 78 28 Ni 50 , the two magic numbers, 28 and 50, are created by spin-orbit interaction, such as 6, 14 or 82. While 20 6 C 14 and 42 14 Si 28 have proven to be deformed [4,5], 132 50 Sn 82 has the major characteristics of a doubly-magic spherical nucleus [6,7]. Thus the actual behavior of 78 Ni deserves to be examined, particularly the size of the shell gaps at Z = 28 and N = 50 when approaching 78 Ni would be a first clue.…”

Halo nuclei, stepping stones across the drip-lines

“…For transfer reactions, being used at lower beam energies near the Coulomb barrier, the experimental techniques are outlined in [18]. A recent example of a selective neutron transfer reaction to study the single particle properties of 133 Sn [19] shows the particular sensitivity of the method, which can also be used to populate continuum states as will be shown for 10 Li. Transfer reactions and direct reactions at higher energies yield similar information on nuclear structure [20] once particular effects related to the reaction mechanisms are taken into account correctly [21].…”