High-spin spectroscopy of ${}^{140}$Nd

The population of the high-spin states in ${}^{140}$Nd was investigated using the reaction ${}^{96}$Zr(${}^{48}$Ca,4$n$). The results from two experiments, one with the EUROBALL array and one with the JUROGAM II+RITU+GREAT setup employing the recoil decay tagging technique, have been combined to develop a very detailed level scheme for ${}^{140}$Nd. Twelve bands of quadrupole transitions and eleven bands of dipole transitions were identified and their connections to low-lying states were established. Calculations using the cranked Nilsson-Strutinsky and the tilted axis cranking models were used to interpret the observed structures. The overall good agreement between the experimental results and the calculations assuming a triaxial shape of the nucleus strongly support the existence of a stable triaxial shape at high spins in this mass region.

Figure 1

Level scheme of ${}^{140}$Nd in which all bands linked to low-lying states are drawn. The highest states of bands Q11 and Q12 have been cut to minimize the shrink of the figure.

Figure 2

Double-gated spectra for bands Q1–Q4 in ${}^{140}$Nd. The gates were set on selected transitions of each band. The transitions marked with asterisks represent the members of the band.

Figure 3

Double-gated spectra for the bands Q5–Q8 in ${}^{140}$Nd. The gates were set on selected transitions of each band. The transitions marked with asterisks represent the members of the band, while the peaks marked with a # are contaminants from other nuclei.

Figure 4

Double-gated spectra for the bands Q9–Q12 in ${}^{140}$Nd. The gates were set on selected transitions of each band. The transitions marked with asterisks represent the members of the band.

Figure 5

Double-gated spectra for bands D1–D4 in ${}^{140}$Nd. The gates were set on selected transitions of each band. The transitions marked with asterisks represent the members of the band.

Figure 6

Double-gated spectra for the bands D5-D8 in ${}^{140}$Nd. The gates were set on selected transitions of each band. The transitions marked with asterisks represent the members of the band.

Figure 7

Double-gated spectra for the bands D9, D10, D11 in ${}^{140}$Nd. The gates were set on selected transitions of each band. The transitions marked with asterisks represent the members of the band.

Figure 8

Calculated potential energy surfaces in the (${\varepsilon }_2,\gamma$) plane for ${}^{140}$Nd, with fixed parity and signature ($\pi =+,\alpha =0$), in the spin range relevant for the observed high-spin bands ($I={24}^{+},{32}^{+},{40}^{+},{48}^{+}$). The contour line separation is 0.25 MeV.

Figure 9

Calculated potential energy surfaces in the (${\varepsilon }_2,\gamma$) plane for the [82,22(20)] configuration assigned to band Q1 of ${}^{140}$Nd. The contour line separation is 0.25 MeV.

Figure 10

The calculated single-particle Routhians at an approximate deformation for the [82,22(20)] configuration drawn as functions of the rotational frequency. The gaps corresponding to this configuration are labeled by rectangles while some other particle numbers are given within circles. The orbitals are labeled by the subshells with the dominating amplitudes and by the ordering within the different groups. The proton $d_{5/2}{g}_{7/2}$ orbitals are labeled $\left(dg\right)$ and the neutron $d_{3/2}{s}_{1/2}$ and $h_{9/2}{f}_{7/2}$ orbitals $\left(sd\right)$ and $\left(hf\right)$, respectively.

Figure 11

The spin contribution in the [82,22(20)] configuration from the different groups of orbitals drawn vs rotational frequency, $\omega$. The total spin contribution from protons is labeled $I_p$ and that from the neutrons $I_n$. The frequencies corresponding to the lowest and highest observed spin values in the [82,22(20)] configuration, $18\hslash$ and $26\hslash$, respectively, are indicated while the value of $I/2$ with $I=I_p+I_n$ is shown in both the proton and the neutron panels. The contribution from the $h_{11/2}$ neutrons, which is labeled ${\left(h_{11/2}\right)}^{-2}$ is actually calculated as the contribution from the ten $h_{11/2}$ orbitals which are occupied. Note that the contributions from the proton and neutron cores and from the $\left(sd\right)$ neutrons, which are drawn at the bottom of the respective diagrams, are essentially negligible.

Figure 12

The configurations with negative parity and odd spin which result from the combination of the three proton configurations with two or three $h_{11/2}$ particles and 19 neutron configurations with up to three high-$j$ particles are drawn relative to the rotating liquid drop energy. The bands which are assigned to an observed band are drawn with heavy lines. Noncollective aligned states are encircled.

Figure 13

The observed Q bands in ${}^{140}$Nd are shown relative to the rotating liquid drop energy in the upper panel, the calculated bands assigned to them are drawn in the middle panel, and the differences between experiment and calculations are presented in the bottom panel. The same types of lines and symbols are used for the related bands in the three panels.

Figure 14

Calculated single-proton Routhians. Full line $\pi =+$, dash-dotted line $\pi =-$. In case of principal axis rotation the signatures $\alpha =\pm 1/2$ are indicated by $\pm$, respectively. $\theta =0$ long axis ($\gamma =-{90}^{\circ }$), $\theta ={90}^{\circ }$ short axis ($\gamma =0^{\circ }$.) The middle panel connects the two axes at the indicated frequency.

Figure 15

Calculated single-neutron Routhians. The line and label conventions are similar to those in Fig. 14.

Figure 16

${}^{140}$Nd $\Delta I=1$ bands D1–D8. The line type indicates the parity: full $\pi =+$, dashed $\pi =-$.

Figure 17

${}^{140}$Nd $\Delta I=1$ bands D9–D11. The line type indicates the parity: full $\pi =+$, dashed $\pi =-$.