Band structures, lifetimes, and shape coexistence in ${}^{130}\mathrm{La}$

The level structure of ${}^{130}\mathrm{La}$ has been investigated using the ${}^{121}\mathrm{Sb}({}^{12}\mathrm{C}$, 3n) reaction with the ROSPHERE array at IFIN-HH, Bucharest. The level scheme was significantly extended with the observation of 45 new states and 100 new transitions. Several band structures have been identified and a clear connection with the lower-lying states has been established. A lifetime of $\tau =3.6\left(2\right)$ ns has been measured for the 346-keV $6^{-}$ state by the in-beam fast timing technique. The lifetimes of 18 high-spin states have been determined by applying the Doppler-shift attenuation method. The deformations derived from the experimental $B\left(E2\right)$ transition strengths indicate distinct coexisting shapes at high spins in ${}^{130}\mathrm{La}$. The experimental properties of both low- and high-spin states were compared with theoretical calculations performed in the frame of the two-quasiparticles-plus-rotor model. Two new negative-parity decoupled bands, with a deduced quadrupole deformation ${\beta }_2=0.150\left(15\right)$, were interpreted by coupling the proton in the 1/2[550] and 3/2[541] orbitals with the odd neutron occupying mainly the low-$\mathrm{\Omega }$ orbitals from the $d_{3/2}$ and $s_{1/2}$ states. A quadrupole deformation ${\beta }_2=0.220\left(17\right)$ was derived for a newly identified positive-parity decoupled band. This enhanced deformation was attributed to the involvement in the band configuration of the $\mathrm{\Omega }=1/2$ $(f_{7/2},h_{9/2})$ intruder neutron orbital. The multiparticle configuration $\pi g_{7/2}{\left(h_{11/2}\right)}^2\otimes \nu \left(h_{11/2}\right)$ was assigned to a high-spin negative-parity dipole band, based on the comparison of the experimental $B\left(M1\right)$ transition strengths with values calculated by applying the geometrical model of Dönau and Frauendorf.

Figure 1

Low-lying level scheme of ${}^{130}\mathrm{La}$ from Ref. [43] and present work. New levels and transitions are drawn with red color. The transitions between states of the same parity are shown as vertical arrows; the transitions connecting states of different parities are shown as tilted arrows. The arrows with energy labels in parentheses indicate unobserved tentative transitions.

Figure 2

Positive-parity bands of ${}^{130}\mathrm{La}$ from Ref. [43] and present work. New levels and transitions are drawn with red color. The lowest level shown is the $7^{+}$ bandhead of band 1 with $E_x=618$ keV.

Figure 3

Negative-parity bands of ${}^{130}\mathrm{La}$. New levels and transitions are drawn with red color. The energy of the lowest-lying state of each observed structure is given to show the connection with the lower-lying states of Fig. 1. The transition of 1036 keV from the ${21}^{-}$ state of band 9, shown as dotted arrow, was not seen in the present work, but was included according to Ref. [31].

Figure 4

(a) Sum of double-gated spectra in band 7 ($375+555$ keV, $375+376$ keV, $550+376$ keV, $550+555$ keV) obtained from the $\gamma -\gamma -\gamma$ cube; (b) Coincidence spectrum from the symmetric $\gamma -\gamma$ matrix gated by transitions in band 9; (c) Sum of double-gated spectra in band 11 ($696+535$ keV, $696+554$ keV, $696+809$ keV, $554+809$ keV, $535+809$ keV) obtained from the $\gamma -\gamma -\gamma$ cube. In all spectra, transitions belonging to the bands or involved in the decay of the bands are marked by energy. The new transitions are marked in red.

Figure 5

Experimental and calculated line shapes for transitions deexciting the states in the band 2 of ${}^{130}\mathrm{La}$ with (a) $J^{\pi }={15}^{-}$, (b) ${16}^{-}$, (c) ${17}^{-}$, and (d) ${21}^{-}$, respectively. The coincidence spectra were created with narrow gates on lower-lying transitions emitted from stopped nuclei. The fitted DSAM spectra are shown in red dashed lines.

Figure 6

Experimental and calculated line shapes for transitions deexciting the states in the band 9 of ${}^{130}\mathrm{La}$ with (a) $J^{\pi }={16}^{-}$, (b) ${17}^{-}$, and (c) ${18}^{-}$, respectively. The coincidence spectra were created with narrow gates on lower-lying transitions emitted from stopped nuclei. The fitted DSAM spectra are shown in red dashed lines.

Figure 7

Experimental and calculated lineshapes for transitions deexciting the states with (a) $J^{\pi }={15}^{+}$ and (b) ${17}^{+}$ in band 7, and (c) ${15}^{-}$ in band 11. The coincidence spectra were created with narrow gates on lower-lying transitions emitted from stopped nuclei. The fitted DSAM spectra are shown in red dashed lines.

Figure 8

Time spectrum for the 114-keV transition obtained he the ${\mathrm{LaBr}}_3$(Ce) detectors when gating on the 272-keV feeding transition.

Figure 9

Experimental low-lying positive-parity states compared to the two-quasiparticles plus rotor model calculations performed for different quadrupole deformations.

Figure 10

Experimental band 2 compared to the two-quasiparticles plus rotor model calculations for quadrupole deformation ${\epsilon }_2=0.14$. The $B\left(E2\right)$ values, expressed in W.u., are shown in red color, while the $B\left(M1\right)$ values, expressed in mW.u., are shown in blue color.

Figure 11

Experimental decoupled band 11 compared to the two-quasiparticles plus rotor model calculations for quadrupole deformation ${\epsilon }_2=0.14$. The experimental and calculated $B\left(E2\right)$ values, expressed in W.u., are shown in red color, while the calculated $B\left(M1\right)$ values, expressed in mW.u., are shown in blue color.

Figure 12

Experimental $B\left(M1\right)$ values derived for states of band 9 compared to calculated values for the candidate configurations.