Spectroscopy of ${}^{98}\mathrm{Ru}$

The ${}^{98}\mathrm{Ru}$ nucleus, populated via the ${}^{97}\mathrm{Mo}({}^3\mathrm{He},2n)$ reaction, has been investigated by means of $K$-internal conversion coefficient, $\gamma$-ray angular distribution, $\gamma -\gamma$ coincidence, and $\gamma -\gamma$ angular correlation measurements. The results have led to an improved knowledge of the excitation energy pattern via the identification of new levels and transitions. New information on spin and parities of many levels as well as on mixing ratios of several transitions has been obtained. The presence of large $M1$ components in many transitions definitely excludes the possibility of considering ${}^{98}\mathrm{Ru}$ as a nucleus having a structure very close to the vibrational one and points to the need of an enlarged framework for a successful description.

Figure 1

Upper panel: $K$- and $L$-conversion lines of the 652.4 keV, $2_1^{+}\to 0_1^{+}$ transition. Lower panel: $K$-conversion line (297.6 keV) of the 319.7 keV transition deexciting the 2867 keV level. It is clearly resolved from the doublet made up by the $K$-conversion lines (302.4 and 303.4 keV) of the 324.4 and 324.5 keV transitions of ${}^{98}\mathrm{Ru}$ and ${}^{97}\mathrm{Tc}$, respectively.

Figure 2

Schematic view of the apparatus utilized in angular distribution and correlation measurements.

Figure 3

Partial energy spectra obtained by gating on (a) the $2_1^{+}\to 0_1^{+}$, 652.4 keV, (b) $4_1^{+}\to 2_1^{+}$, 745.4 keV, (c) $6_1^{+}\to 4_1^{+}$, 824.7 keV transitions and on (d) a small region around 1722 keV. The 1774.5 keV transition deexciting the 2427 keV level is shown to give an idea of the FWHM of the lines in this energy region. The arrows in panels (a) and (b) mark the presence of new transitions found in this work (see text per detail).

Figure 4

(a) Section of the $\gamma$ energy spectrum obtained by gating on the 761.8, $2_2^{+}\to 2_1^{+}$ keV transition. The 1256.1 and 1293.0 keV transitions deexcite the 2670 and 2707 keV levels, respectively. (b), (c) Section of the $\gamma$ energy spectrum obtained by gating on (b) a region around 1256–1258 keV and (c) the 1293.0 keV transition. The presence in panel (b) of the 745.4 keV transition is due to decay of the 2656 keV level to the $4_1^{+}$ state via the 1258.7 keV transition.

Figure 5

Angular distribution of the 903.8 (upper panel) and 984.4 keV (lower panel) transitions deexciting the 3126 and 3251 keV levels, respectively. The continuous curve represents the function $W\left(\theta \right)$ evaluated with the fitted parameters. The reported values (on an arbitrary scale) correspond to the data collected in a single run.

Figure 6

Attenuation coefficient ${\alpha }_2$ as a function of $J_i$.

Figure 7

Comparison of the experimental $A_{22}$ coefficient of the 1149.2 keV transition, deexciting the 2547 keV level to the $4_1^{+}$ state, with the values calculated for three values of the attenuation coefficient [$\alpha 2=0.30$ (dotted line), 0.35 (full line), and 0.40 (dashed line); see text for details], as a function of $\delta$, for $Ji=5$. Upper panel: Extended range of $\delta$. Horizontal lines mark the experimental values (full line) and the associated uncertainties (dotted lines). Lower panel: Expanded view of the $\delta =0–5$ region. Full vertical lines mark the deduced value of $\delta$, while dotted vertical lines mark the associated uncertainties.

Figure 8

Plot of ${\chi }^2$ versus arctan($\delta$) for the different hypotheses on the spin of the uppermost state of the reported cascades starting from the 1817 keV (upper panel) and 2246 keV (lower panel) levels, respectively.

Figure 9

Decay level scheme of ${}^{98}\mathrm{Ru}$ up to $\sim 2400$ keV. Energies of levels and transitions are given in keV. New information on $J^{+}$ is reported in boldface characters.

Figure 10

Same as for Fig. 9 except for levels above 2400 keV.

Figure 11

Same as for Fig. 9 except for levels above 2800 keV.

Figure 12

Same as for Fig. 9 except for levels above 3100 keV.

Figure 13

Same as for Fig. 9 except for levels above 3500 keV.