Decay of the $I^{\pi }=8^{-}$ isomeric state in ${}^{134}\mathrm{Nd}$ and ${}^{184}\mathrm{Pt}$ studied by electron and $\gamma$ spectroscopy

The properties of the $K$-isomer decays in the ${}^{134}\mathrm{Nd}$ and ${}^{184}\mathrm{Pt}$ nuclei have been investigated. Measurements were carried out in $e-\gamma$ and $\gamma -\gamma$ coincidence modes using electron spectrometers coupled to the central European Array for Gamma Levels Evaluations at the Heavy Ion Laboratory of the University of Warsaw. Internal conversion coefficients were obtained for transitions relevant to the decay of the isomeric states, allowing the determination of multipolarities and mixing ratios as well as hindrance factors. Two possible causes of the weakening of the $K$ forbiddenness, namely rotational $K$ mixing (Coriolis interaction) and triaxiality, are briefly discussed using schematic theoretical models.

Figure 1

The decay scheme of the $I^{\pi }=8^{-}, K=8$ isomeric state in ${}^{134}\mathrm{Nd}$ ($N=74$) [10, 11].

Figure 2

The decay scheme of the $I^{\pi }=8^{-}$ isomeric state in ${}^{184}\mathrm{Pt}$ ($N=106$) [13]. The width of the solid rectangles at the top of the arrows is proportional to the relative $\gamma$ intensity from a given level.

Figure 3

The efficiency curve (${\epsilon }_{\gamma }/{\epsilon }_e$) of the experimental setup for the ${}^{134}\mathrm{Nd}$ measurement. The linear fit to the experimental points and the error band are indicated by solid and dashed lines, respectively.

Figure 4

The summed electron spectrum in coincidence with the 294-, 495-, and 631-keV $\gamma$ transitions accompanying the decay of the isomeric state in ${}^{134}\mathrm{Nd}$ (see also Fig. 1). The experimental (thick solid line) and simulated (for more details, see text) K874 lines, for $M2$ and $E3$ multipolarities, are shown for comparison in the inset.

Figure 5

The $\gamma$ spectra (thin solid lines, left ordinate) gated on the 294-keV line collected during two time spans (see text) after the end of the cyclotron beam pulse. The weak 596-keV $\gamma$ line is visible in the difference spectrum (thick solid line, right ordinate). This proves that the $8^{-}$ isomeric state in ${}^{134}\mathrm{Nd}$ also decays to the $\gamma$ band, as was suggested in Ref. [10].

Figure 6

The total electron spectrum (dotted line, left ordinate) and the spectrum gated on the 163-keV $\gamma$ line (solid line, right ordinate) for the ${}^{184}\mathrm{Pt}$ “beam-off” measurement.

Figure 7

The efficiency curve (${\epsilon }_{\gamma }/{\epsilon }_e$) vs electron energy for the experimental setup (${}^{184}\mathrm{Pt}$ experiment). The third-order polynomial fit to the experimental points and the error band are denoted by solid and dashed lines, respectively.

Figure 8

Sum of the electron spectra (thin solid line) in coincidence with the 441- and 1071-keV $\gamma$ rays from the ${}^{184}\mathrm{Pt}$ experiment. For the 119-keV transition the experimental spectrum may be compared with the simulated one (thick solid line) for ${\delta }^2=0.7$.

Figure 9

The sum of the electron spectra gated on the 163- and 871-keV $\gamma$ lines from ${}^{184}\mathrm{Pt}$. The thick solid line represents a Gaussian function (superimposed on a constant background) fitted to the experimental points. All peak parameters were fixed except the area.

Figure 10

Experimental alignments for ${}^{134}\mathrm{Nd}$ and ${}^{184}\mathrm{Pt}$. Harris reference parameters of ${\mathcal{I}}_0=17.0{\hslash }^2{\mathrm{MeV}}^{-1}$ and ${\mathcal{I}}_1=25.0{\hslash }^2{\mathrm{MeV}}^{-1}$ (the same as in Ref. [3]) were used for both nuclei.

Figure 11

Mean-field collective potential energy (relative to a spherical shape) for ${}^{134}\mathrm{Nd}$ and ${}^{184}\mathrm{Pt}$ (see text).