Exotic rotations, triaxiality and shape coexistence in A = 130-140 nuclei

Speaker: 
Costel Petrache (Université Paris-Sud)
Event Date and Time: 
Thu, 2015-08-20 14:00 - 15:00
Location: 
TRIUMF Auditorium


The existence of triaxial nuclei has been the subject of a long standing debate. The possibility of soft and rigid triaxiality has been proposed very early, and many theoretical and experimental studies have been devoted to this intriguing phenomenon since then. More recently two unique fingerprints of triaxiality in nuclei have been intensively studied: the wobbling motion and the dynamic chirality. We have recently studied the Nd nuclei up to very high spins and identified a multitude of bands, which were interpreted as the manifestation of a stable triaxial nuclear shape, presenting various types of collective motion: tilted axis and principal axis rotation, wobbling motion, chiral bands [1,2]. We will discuss the global features of the investigated nuclei, like the J (2) moments of inertia and their theoretical interpretation, as well as the conclusions we have drawn, some of them quite surprising, from the systematic study of the high-spin structure of the Nd nuclei from 128Nd to 141Nd [2].

The existence of triaxial nuclei has been the subject of a long standing debate. The possibility of soft and rigid triaxiality has been proposed very early, and many theoretical and experimental studies have been devoted to this intriguing phenomenon since then. More recently two unique fingerprints of triaxiality in nuclei have been intensively studied: the wobbling motion and the dynamic chirality. We have recently studied the Nd nuclei up to very high spins and identified a multitude of bands, which were interpreted as the manifestation of a stable triaxial nuclear shape, presenting various types of collective motion: tilted axis and principal axis rotation, wobbling motion, chiral bands [1,2]. We will discuss the global features of the investigated nuclei, like the J (2) moments of inertia and their theoretical interpretation, as well as the conclusions we have drawn, some of them quite surprising, from the systematic study of the high-spin structure of the Nd nuclei from 128Nd to 141Nd [2].

The wobbling motion has been first observed in odd-A triaxial strongly deformed nuclei around Z = 72, N = 94 [3], in which case the odd proton occupying an orbital with high intrinsic angular momentum and having a predominantly particle nature aligns its angular momentum vector along the rotation axis (the medium axis, corresponding to the largest moment of inertia). This type of collective motion is called "longitudinal wobbling", which is different from the recently predicted [4] and observed [5] wobbling motion in odd-A nuclei around Z = 60, N = 74, called "transverse wobbling", in which the odd proton aligns its angular momentum along the short axis of the triaxial rotor, which is perpendicular to the rotation axis. We will discuss the experimental evidence of this new type of collective motion, the transverse wobbling, in A=130-140 nuclei. Another phenomenon revealed by our recent results on the high-spin structure in Nd nuclei with neutron numbers just below the N=82 shell closure is the shape coexistence. It is induced by the existence of high-spin seniority isomers built on a spherical shape which are surrounded by triaxial bands [6]. The implications of the newly identified high-spin isomers will be discussed.

[1] R. Leguillon et al., Phys. Rev. C 88, 014323 (2013).
 [2] C.M. Petrache et al., Phys. Rev. C 86 (2012) 044321; Phys. Rev. C 88 (2013) 051303(R); Phys. Rev. C 91 (2015) 024302; Phys. Scr., in print.
[3] S.W. Odegard et al., Phys. Rev. Lett. 86, 5866 (2001).
[4] S. Frauendorf and F. Doenau, Phys. Rev. C 89, 014322 (2014).
[5] J.T. Matta et al., Phys. Rev. Lett. 114, 082501 (2015). [6] C.M. Petrache et al., submitted.


 

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