High-precision measurements of low-lying isomeric states in ${}^{120–124}\mathrm{In}$ with the JYFLTRAP double Penning trap

Neutron-rich ${}^{120–124}\mathrm{In}$ isotopes have been studied utilizing the double Penning trap mass spectrometer JYFLTRAP at the IGISOL facility. Using the phase-imaging ion-cyclotron-resonance technique, the isomeric states were resolved from ground states and their excitation energies measured with high precision in ${}^{121,123,124}\mathrm{In}$. In ${}^{120,122}\mathrm{In}$, the $1^{+}$ states were separated and their masses were measured while the energy difference between the unresolved $5^{+}$ and $8^{-}$ states, whose presence was confirmed by post-trap decay spectroscopy, was determined to be $\le 15$ keV. In addition, the half-life of ${}^{122}\mathrm{Cd}$, $T_{1/2}=5.98\left(10\right)\mathrm{s}$, was extracted. Experimental results were compared with energy density functionals, density functional theory, and shell-model calculations.

Figure 1

Projection of the cyclotron motion of ${}^{120}\mathrm{In}^{+}$ ions on the position-sensitive detector obtained with the PI-ICR technique using a phase accumulation time $t_{\mathrm{acc}}=595$ ms. Only bunches with a single detected ion are shown.

Figure 2

$\beta$-gated $\gamma$-ray spectrum obtained for ${}^{120}\mathrm{In}$ and ${}^{120}\mathrm{Cd}$ produced in fission reactions of ${}^{\mathrm{nat}}\mathrm{U}$ and purified in the first trap, see text for details. The energies shown in blue and orange indicate the transitions from the $5^{+}$ and $8^{-}$ states in ${}^{120}\mathrm{In}$, respectively, in grey the transition that is common for the $5^{+}$ and $8^{-}$ states, in black the transition that is common for the $1^{+}$, $5^{+}$, and $8^{-}$ states.

Figure 3

Projection of the cyclotron motion of ${}^{122}\mathrm{In}^{+}$ ions on the position-sensitive detector obtained with the PI-ICR technique using a phase accumulation time $t_{\mathrm{acc}}=1014$ ms. Ions of ${}^{122}\mathrm{In}$ were produced in proton-induced fission of ${}^{\mathrm{nat}}\mathrm{U}$. The spin assignment is based on the post-trap spectroscopy measurements and the mass measurement of ${}^{122}\mathrm{In}^{2+}$ ions produced after $\beta$ decay of ${}^{122}\mathrm{Cd}$, see text for details.

Figure 4

$\beta$-gated $\gamma$-ray spectrum obtained for ${}^{122}\mathrm{In}$ produced in fission reactions of ${}^{\mathrm{nat}}\mathrm{U}$ and purified in the first trap. The energies shown in blue and orange indicate the transitions from the $5^{+}$ and $8^{-}$ states in ${}^{122}\mathrm{In}$, respectively, in grey the transition that is common for the $5^{+}$ and $8^{-}$ states, in black the transition that is common for the $1^{+}$, $5^{+}$, and $8^{-}$ states.

Figure 5

A comparison of two-neutron separation energies $S_{2n}$ (a), two-neutron shell-gap energies ${\delta }_{2n}$ (b), and three-point neutron gaps ${\mathrm{\Delta }}_n^{\left(3\right)}$ (c) between experimental values from this work and AME2020 [33], and the theoretical models: BSkG1 (blue diamonds), BSkG2 (orange pentagons), SLy4 (purple triangles), SV-min (brown $+$ symbols), UNEDF0 (grey $x$ symbols), and UNEDF1 (green hexagons). For the ground state of ${}^{122}\mathrm{In}$, only the statistical uncertainty was included.

Figure 6

A comparison of (a) two-neutron shell-gap energies ${\delta }_{2n}$ and (b) three-point neutron gaps ${\mathrm{\Delta }}_n^{\left(3\right)}$ for the even-$N$ cadmium, indium, and tin isotopic chains. Data are taken from AME2020 [33] and this work. For the ground state of ${}^{122}\mathrm{In}$, only the statistical uncertainty was included.

Figure 7

Comparison of the experimental (Exp.) and shell model (SM) schemes of excited states in ${}^{120,122,124}\mathrm{In}$ up to 400 keV. The experimental scheme is based on this work and adjusted results from Refs. [55, 61, 71].