Orbital Dependent Nucleonic Pairing in the Lightest Known Isotopes of Tin

Abstract

By studying the (109)Xe→(105)Te→(101)Sn superallowed α-decay chain, we observe low-lying states in (101)Sn, the one-neutron system outside doubly magic (100)Sn. We find that the spins of the ground state (J=7/2) and first excited state (J=5/2) in (101)Sn are reversed with respect to the traditional level ordering postulated for (103)Sn and the heavier tin isotopes. Through simple arguments and state-of-the-art shell-model calculations we explain this unexpected switch in terms of a transition from the single-particle regime to the collective mode in which orbital-dependent pairing correlations dominate.

γ-ray spectroscopy of the odd-oddN=Z+2deformed proton emitter112Cs

“…If this is indeed a second proton decay in 112 Cs, then the energy difference between this decay and the known 112 Cs proton decay is 100 keV. This is interesting since the daughter nucleus 111 54 Xe is known to decay by two alpha-decay branches with an energy difference close to 100 keV [7,8] [31] and its fine structure [32] have given information about the first excited state in 101 Sn. However, with the low numbers of counts and large uncertainties in the present work, it is not possible to draw any definite conclusion about the states in 111 Xe.…”

Experimental study of the decays of112Cs and111Xe

“…In this case we have used the same shell model calculations as employed in the 105 Te decay study [3] which are derived from nucleon scattering potentials [37]. The nucleon-nucleon potential AV18 [38] was used.…”

“…This renders the region of the nuclidic chart above 100 Sn particularly interesting for probing nuclear structure, since protons and neutrons outside the closed shells occupy orbitals with the same quantum numbers. It is expected that some of these nuclei may have an unusually large reduced alpha-decay width, resulting in the so-called superallowed alpha decay [1][2][3]. Another interesting feature of this portion of the chart of nuclei is the presence of the proton drip-line.…”

Nucleon pair approximation description of the low-lying structure of108,109Te and109I

“…The neutron single-particle energies of g 7/2 and d 5/2 orbitals are taken from the experimental excitation energies in 101 Sn [8]. There are no experimental data for the remaining orbitals.…”

“…Great experimental and theoretical efforts have been made in recent years to study the structure and decay properties of neutron-deficient tin, tellurium, iodine and xenon isotopes near the N = Z = 50 closed shells [1][2][3][4][5][6][7][8][9][10][11][12]. Towards the proton drip line, these nuclei become unstable against particle emissions [13][14][15][16].…”