Schottky mass measurements of heavy neutron-rich nuclides in the element range $70\le Z\le 79$ at the GSI Experimental Storage Ring

Storage-ring mass spectrometry was applied to neutron-rich ${}^{197}$Au projectile fragments. Masses of ${}^{181,183}$Lu, ${}^{185,186}$Hf, ${}^{187,188}$Ta, ${}^{191}$W, and ${}^{192,193}$Re nuclei were measured for the first time. The uncertainty of previously known masses of ${}^{189,190}$W and ${}^{195}$Os nuclei was improved. Observed irregularities on the smooth two-neutron separation energies for Hf and W isotopes are linked to the collectivity phenomena in the corresponding nuclei.

Figure 1

Example of a Schottky frequency spectrum with the corresponding isotope identification. This spectrum is combined from eight independent injections acquired for the electron-cooler voltage $U_c=209$ kV. Nuclides with known and previously unknown masses are indicated by different fonts (see legend).

Figure 2

A zoomed-in view of the Schottky frequency spectrum illustrated in Fig. 1 on a quadruplet of $A=190$ isobars. The peaks corresponding to nuclides in isomeric states are labeled with $m$.

Figure 3

A part of the chart of nuclides indicating the nuclides measured in this work as well as the nuclides in the ground and isomeric states identified in the other part of this experiment devoted to the search for new K isomers in this region [10, 11].

Figure 4

Top: Mass-to-charge ratio $m/q$ as a function of revolution frequency. The solid line illustrates a straight-line fit through the calibration $m/q$ values. Bottom: The same as the top but with the linear fit subtracted.

Figure 5

Data for the $A\sim 180$ region, two-neutron separation energies [28] as a function of neutron number from $N=100$ to $N=124$ for even $Z$ (left) from Dy to Pt and odd $Z$ (middle) from Ho to Re. The new $S_{2n}$ values obtained from this work are shown in red while the literature $S_{2n}$ values are shown in black. Right: Energies of the first excited 2${}^{+}$ states [32] for the same even-even nuclei as in the left panel.

Figure 6

The symmetry triangle of the IBA showing the three dynamical symmetries at the vertices. The colors indicate calculated collective contributions in MeV to binding energies for $N_B=5$ (left) and $N_B=16$ (right). A similar triangle for $N_B=16$ was presented in Ref. [8].

Figure 7

$P$-factor values illustrated with a color code for even-even nuclei in the $Z=50–82$ and $N=82–126$ shells. Black points marked are for the key nuclei discussed, namely, ${}^{190}$W, ${}^{196}$Os, ${}^{188}$Pt, ${}^{198}$Pt, and ${}^{152}$Sm.

Figure 8

Calculated $E$(2${}_1^{+}$) (top), $\delta E$(2${}_1^{+}$) (middle), and $\delta S_{2n-\mathrm{coll}}$ (bottom) values from IBA calculations as a function of boson number $N_B$. The points for $\delta E$(2${}_1^{+})$ and $\delta S_{2n-\mathrm{coll}}$ correspond to a set of schematic IBA calculations in which $\kappa$, and $\chi$ are constant (at 0.02 and $-1.32$, respectively) while $\epsilon$ and $N_B$ vary in a smooth way to simulate a spherical-to-deformed transition region. The following equations are used for $\delta E$(2${}_1^{+}$) and $\delta S_{2n-\mathrm{coll}}$: $\delta E\left(2_1^{+}\right)(Z,N)=[E\left(2_1^{+}\right)(Z,N)-E\left(2_1^{+}\right)(Z,N+2)]/E\left(2_1^{+}\right)(Z,N)$ and $\delta S_{2n-\mathrm{coll}}=-[S_{2n-\mathrm{coll}}(Z,N)-S_{2n-\mathrm{coll}}(Z,N+2)$], respectively.

Figure 9

Experimental $E$(2${}_1^{+}$) (top) and $S_{2n}$ (bottom) values vs neutron number for ${}_{62}$Sm [29, 32].