Signature inversion in 120Cs: Evidence for a residual pn interaction

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

“…The data for 114−126 Cs are taken from Refs. [3,17,21,22,[37][38][39][40][41] with spin assignments from Ref. [42].…”

Excited states and signature inversion inCs116

“…Prior to the present work, signature-inversion frequencies had been identified in the ν(h 11/2 ) ⊗ π (h 11/2 ) bands of the Z = 55 118−126 Cs isotopes [11][12][13][14][15][16][17][18]; the most neutron-deficient odd-odd cesium isotope in which excited states had been observed was 118 Cs 63 [12]. It is expected that the np interaction will increase in significance when approaching N = Z, so it is important that the more neutron-deficient isotopes be studied, in order to set apart the different theoretical interpretations.…”

Quadrupole pairing interaction and signature inversion

“…Semmes and Ragnarsson [13] considered a residual pn contact force with spin-spin interaction, V pn ∝ δ(r p − r n )(u 0 + u 1 σ n · σ p ), in the framework of the particle-rotor model. Remarkably, using one set of parameters u 0 , u 1 , it appeared possible to reproduce very accurately some πh 11/2 νh 11/2 bands in the A∼130 region and πh 11/2 νi 13/2 bands in rare-earth nuclei, without invoking triaxiality [10,14]. However, to account for the πh 9/2 νi 13/2 bands in rare-earth nuclei, a substantial reduction of the strength parameters u 0 and u 1 was necessary [15].…”

“…The general condition for signature inversion to take place [4] was positive triaxial deformation, γ > 0, within the Lund convention combined with a specific position of the Fermi surface, see also [8,9]. One should point out, however, that (i) the γ-values are almost impossible to measure directly in experiment; (ii) the values of the γ parameter necessary to account for the experimental data are not always supported by potential energy calculations which in many cases predicts almost axial shapes [10]. Triaxiality seems, therefore, to be not always sufficient calling for alternative or supplementary mechanism.…”