Z. Phys. A354, 5-6 (1996) Short note ZEITSCHRIFT FOR PHYSIK A © Springer-Verlag 1996 Yrast bands and signature inversion in doubly odd 162, 164Lu M.A. Cardona t, M.E. Debray L 2" 4, D. Hojman l" 3, 5, A.J. Kreiner ~" 3.4, H. Somacal 1' 5, j. Davidson 2, 3, M. Davidson 2" 3, D. De Acufia 6, D.R. Napoli 6, J. Rico 6, D. Bazzacco 7, R. Burch 7, S.M. Lenzi 7, C. Rossi Alvarez 7, N. Blasi s, G. Lo Bianco 8 ' Departamento de Ffsica, Comisi6n Nacional de Energfa At6mica, 1429 Buenos Aires, Argentina 2 Departamento de Ffsica, Facultad de Ciencias Exactas y Naturales, UBA, Buenos Aires, Argentina 3 CONICET, 1033 Buenos Aires, Argentina "~ Escuela de Ciencia y Tecnologfa, Universidad Nacional de Gral. San Martin 5 Instituto de Tecnolog/a, CNEA-Universidad Nacional de Gral. San Martfn 6 INFN, Laboratori Nazionali di Legnaro, 1-35020 Legnaro, Italy 7 Dipartimento di Fisica, Sezione di Padova, 1-35131 Padova, Italy 8 Dipartimento di Fisica and INFN, Sezione di Milano, 1-20133 Milano, Italy Received: 23 October 1995 Communicated by B. Herskind Abstract: High spin rotational bands in tS2Lu and 164Lu have been studied through the tagLa(2SSi,5n) and tSgLa(29(a°)Si,4(5)n) reactions respectively. For both nuclei the yrast sequence which is associated with the 7rhtl/2 ® ui13/2 configuration shows ~he sig- nature inversion feature. PACS: 23.20.Lv; 27.70.+q Signature dependent effects have been known for a long time [1]. Perhaps the most famous one is the level staggering present in f}--1/2 bands [1] which im- plies an energy separation of the two AI--2 sequences in a rotational band and which is related to the pres- ence of a diagonal matrix element of the Coriolis in- teraction linking the "direct" and the "R-reflected" parts of the rotational wave function [1]. This matrix element is proportional to a phase (equal to (- 1) I+V2 which may be identified with the signature quantum number) and an intrinsic matrix element called the decoupling parameter, a. This diagonal matrix ele- ment only exists for odd-mass systems. For doubly odd nuclei the equivalent matrix element is non diag- onal [2] and connects the K--0=f2n-flp--1/2-1/2 and K=l=f2n+F~p--1/2-fl/2 states being proportional to %+(-!)l+tan. This leads to the rule [2] that bands which involve orbits with decoupling parameters (a,~ and %) of equal sign imply favored odd spin AI--'2 sequences while unequal signs are related to favored even-spin sequences. In this context the phenomenon of signature inversion, namely the inversion of the above mentioned energy separation trend, at low spin of a rotational band came unexpected [3,4]. In partic- ular signature inversion has been observed in odd-odd nucleibelonging to the light rare earth region (Eu, Tb, Ho, Tin) concerning the ~rh11/2 @ viza/~ structure [5]. Very little was hitherto known about doubly odd light Lu isotopes, and in order to go further in the systematics, high spin states in te2,te4Lu were stud- led. Similar investigations are currently in progress [6,7]. The excited states of imLu were populated through IagLa(28Si,5n) at 160 MeV and tS4Lu through lagLa(a°si,5n) and tS~La(29Si,4n) at 157 and 145 MeV bombarding energies respectively. The beams were provided by the Tandem XTU accelerator of Leg- naro and a lmg/cm 2 La, gold backed(4 mg/cm 2) target foil was used. The experimental set-up con- sisted of the 4z" GASP array, composed basically of 40 Compton suppressed large volume Ge detectors and an 80 BGO-element multiplicity filter. Events were collected when at least 3 suppressed Ge and 3 multiplicity filter detectors fired. The assignment of 7-rays to 162,I64Lu was based on coincidences with Lu K X-rays, previous knowledge of the neighboring Lu isotopes (lst,tea,tSSLu) [8,9,10] and BGO multiplicity distribution. The most strongly populated bands ob- served for the te2,t64Lu isotopes studied in the present work are shown in fig. 1, compared with similar struc- tures belonging to is°,teeLu [11,12]. The spin, parity and the configuration lrhit/2® uiia/2 assigned to these bands are based on systematics of odd-odd neighbor- ing nuclei. The spin assignment has been changed by one unit in 166Lu as compared to the original publi- cation [12] to agree with systematics. Fig. 2 shows the systematic variation of the staggering and signa- ture inversion features for all (Trhlt/2 ® uixa/2) known bands in the light rare earth region. From fig. 2 the evolution of the phase inversion point increasing