z. Phys. A 352, 5-6 (1995) Short note ZEITSCHRIFT FORPHYSIKA 9 Springer-Verlag 1995 Dipole rotational band in 137Nd C.M. Petrache 1"*, S. Lunardi J, D. Bazzacco 1, M.A. Rizzuto 1,5, C. Rossi-Alvarez l, R. Venturelli 1, F. Brandolini 1, N.H. Medina 1,**, G. de Angelis 2, G. Bonsignori 3, M. Savoia 3, D. Vretenar 4 Dipartimento di Fisica and INFN, Sezione di Padova, Padova, Italy 2 INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy 3 Dipartimento di Fisica and INFN, Sezione di Bologna, Bologna, Italy 4 Physics Department, Faculty of Science, University of Zagreb, Zagreb, Croatia 5 Istituto de Fisica, Universidade de Sao Paolo, Sao Paolo, Brazil Received: 13 March 1995 Abstract. A dipole band with regular energy spacings has been identified in the nucleus 137Nd built on a I= 33/2 state at Ex=5.60 MeV. The Doppler shift attenuation method analysis of a backed-target experiment allowed to extract the lifetimes of the band levels, which are of the order of 1 W. u.. The resulting large B(M1) values, togeth- er with the high aligned angular momentum suggest a five-quasiparticle configuration (involving two hi1/2 pro- tons and two h1~/2 neutrons). PACS: 21.10.Re; 23.20.Ck; 27.60+j The nuclei of the A~,130-140 mass region are characterized by "/-softness, which favours the coexistence of different shapes [1]. The proton Fermi surface lies at the bottom of the hit/2 sub-shell, while the neutron Fermi surface lies just below the N=82 shell closure, at tile top of the hll/2 sub-shell. This fact determines the particle (hole) char- acter of the valence proton (neutron) and characterizes the 7-driving force on the core. The large signature split- ting observed in the yrast bands of the odd-N nuclei in this mass region points to a significarlt triaxiality at low spins, which induces similar crossing frequencies for the rotational ali~gnment of rrhlt/~ or vht 1/2 pairs. This is the case for the N=77 nucleus laTNd, which, as it results from a recent study with the GASP array [2], exhibits at the same excitation energy bands based on prolate and oblate configurations, as well as highly-deformed and dipole ro- tational bands. In this short note we report on the observation of a dipole rotational band in 137Nd, whose B(M1) transi- tion probabilities are of the order of ~1 W.u.. The e.xis- tence of AI=I rotational bands based on either prolate or oblate shapes has been established since long in the A=130 mass region [3], with characteristics similar to those of the shears bands identified in the lead nuclei [4]. However, a * Permanent address: Institute of Physics and Nuclear Engineering, Bucharest, Romania ** Supported by CNPq, Brazil definitive conclusion concerning the common origin of the AI=I bands in the A=190 and A=130 mass regions could not be drawn, due to the lack of lifetime measurements in the lower mass region. 2000 1500 1000 500 09 ,4--' c 0 0 1500 (D 1000 500 350 Gate 423 keV (thin target) 458 528 596 b) Gate 423 keY (thick target) 458 528 400 450 500 550 650 Energy (keY) Fig. 1. a) High energy part of doubly-gated spec- trum, with gates set on transitions in the dipole rotational band of 137Nd, obtained in the 11~ pd+3~ Si reaction us- ing thin self-supporting targets, b) Same as a) but for the tz3Sb+lg F thick-target reaction (on top of the broad 596 ke V transition appears another narrow 596 ke V peak, coming from a low-lying coincident transition in lar Nd).