Development of collective structures over noncollective excitations in ${}^{139}$Nd

High-spin states in ${}^{139}$Nd were investigated using the reaction ${}^{96}$Zr(${}^{48}$Ca,5$n$) at a beam energy of 195 MeV and $\gamma$-ray coincidences were acquired with the Euroball spectrometer. Apart from several dipole bands at medium excitation energy, three quadrupole bands have been observed at high spin. Linking transitions connecting two of the high-spin bands to low-energy states have been observed. Calculations based on the cranked-Nilsson-Strutinsky formalism have been used to assign configurations for the high-spin quadrupole bands.

Figure 1

Partial level scheme of ${}^{139}$Nd. Energy values of levels important to our discussion have been shown only.

Figure 2

High-energy bands in ${}^{139}$Nd. Energy values of levels important to our discussion have been shown only.

Figure 3

Triple-gated sum spectrum for band 1 in ${}^{139}$Nd. The gates were set on all transitions of the band. The transitions marked with asterisks represent the members of the band.

Figure 4

Triple-gated sum spectrum for band 2 ${}^{139}$Nd. The gates were set on all transitions of the band. The transitions marked with asterisks represent the members of the band.

Figure 5

Triple-gated sum spectrum for band 3 in ${}^{139}$Nd. The gates were set on all transitions of the band. The transitions marked with asterisks represent the members of the band.

Figure 6

States in ${}^{139}$Nd obtained by coupling of a quasihole in 1$\nu h_{11/2}$ orbital to the core states in ${}^{140}$Nd. The corresponding core states are also shown. See text for details.

Figure 7

Dynamic moment of inertia for the collective bands in ${}^{139}$Nd.

Figure 8

Calculated configurations relative to a rotating liquid drop reference for the triaxial high-spin bands in ${}^{139}$Nd. Solid and dashed lines are used for positive and negative parity configurations, respectively. Closed symbols are used for signature $\alpha =1/2$ and open symbols for signature $\alpha =-1/2$. The thick lines and large symbols are used to draw the configurations of our preferred assignments for the high-spin bands in ${}^{139}$Nd. The shapes of the curves are relatively insensitive to the single-particle parameters while absolute energies of the different bands are much more sensitive to the parameters, that is, to the position of the different $j$ shells. Therefore, it is not really a problem that with present parameters, the configurations which are tentatively assigned to the observed bands are calculated a few hundred kilo-electron-volts above yrast.

Figure 9

Comparison between the experimental (upper panels) and theoretical (middle panels) excitation energy relative to a rotating liquid drop reference and their differences (lower panels) for the high-spin bands in ${}^{139}$Nd. Bands 1 and 2 are compared with several calculated configurations in the left and right panels, respectively. Furthermore, a possible assignment of band 3 as a signature partner of band 1 is illustrated in the left panels. Solid and dashed lines and closed and open symbols are used as in Fig. 8. Symbols and colors are used as defined in the legends for the calculated configurations in the middle panels and for their comparison with the observed bands in the lower panels. The same symbols and colors are used for the experimental bands and our preferred assignment.

Figure 10

Spin vs transition energy for the high-spin bands in ${}^{139}$Nd and for the calculated configurations which are tentatively assigned to them.