Twin backbending in 156Dy

Experimental evidence for low-spin members of ?upper? bands in156Dy

“…It is the purpose of the present paper to describe our experimental evidences for the existence and properties of these states. The (p, 4nv) reaction used in the present work has the property of being somewhat less selective than the (e, x n V) and (heavy ions, x n V) reactions which strongly favour the excitations of the yrast levels: the former reaction also populates, although rather weakly, yrare as well as higher states, like those of the v-band in t56Dy which we have previously located up to the 9 + and may be l l~-levels [10,11,19]. We have also compared the v-ray spectra obtained after the (p, 4n) and (14N, 5n) reactions on odd-Z targets in the rareearth region leading to even-even final nuclei [19], and found that those from the former reaction are much richer than those from the latter which essentially include transitions in the g.s.…”

“…Cases (1) and (3) imply a K=0 character for the upper bands, whereas case (2) allows K 4: 0. The discrimination between K equal to or different from 0 can be carried out experimentally by looking for oddspin members of the upper bands, which are not allowed for K~=0 § In the course of an experimental investigation of the energy levels in 156Dy through the 159Tb(p ' 4 n 7) 156Dy reaction, of which the first results have been described previously [10,11], we have located six new states in this nucleus between 1.8 and 2.8 MeV. The excitation energies and spins of some of these levels seem to correspond to members of upper bands referred to above; in particular, they are reasonably close to states predicted by the calculations just mentioned [15].…”

“…1. Experimental data [10][11][12] on the nucleus 156Dy presented in a E(J) versus J(J+ 1) diagram, where J is the spin and E(J), the excitation energy of the levels in this nucleus. The unprimed numbers indicate the spins of the yrast levels [7], the primed ones, those of the yrare levels [7]; they are connected by heavy solid lines which are the yrast and yrare bands.…”

“…In Ref. 15, the available experimental data [10][11][12] on t56Dy have been fitted by mixing several bands, characterized by the projection K of the angular momentum J along the nuclear symmetry axis: no satisfactory fit can be achieved by mixing three K = 0 bands, a reasonable agreement is obtained with K-0, 0 and 1 bands, corresponding to the g.s., //-and third bands, respectively, and even better fits result from the interaction between more than three bands, of which the lower two have K=0 and the others, K4:0. This would suggest that the "third" band may not be unique, but rather consists of several bands, to which we shall refer in the following as "upper" bands.…”

“…8, 9), up to 22 and 20, respectively, in X56Dy (Refs. [10][11][12], and up to 20 and 18, respectively, in 154Dy (Ref. 13); the data on X56Dy are displayed in Fig.…”