First identification of excited states in ${}^{117}\mathrm{Ba}$ using the recoil-$\beta$-delayed proton tagging technique

Excited states have been observed for the first time in the neutron-deficient nucleus ${}^{117}\mathrm{Ba}$ using the recoil-decay tagging technique following the heavy-ion fusion-evaporation reaction ${}^{64}\mathrm{Zn}$(${}^{58}\mathrm{Ni}$, 2p3n)${}^{117}\mathrm{Ba}$. Prompt $\gamma$ rays have been assigned to ${}^{117}\mathrm{Ba}$ through correlations with $\beta$-delayed protons following the decay of $A=117$ recoils. Through the analysis of the $\gamma -\gamma$ coincidence relationships, a high-spin level scheme consisting of two bands has been established in ${}^{117}\mathrm{Ba}$. Based on the systematics of the level spacings in the neighboring barium isotopes, the two bands are proposed to have $\nu h_{11/2}\left[532\right]5/2^{-}$ and $\nu d_{5/2}\left[413\right]5/2^{+}$ configurations, respectively. The observed band-crossing properties are interpreted in the framework of cranked shell model.

Figure 1

Energy spectra of (a) all decays measured in the DSSD and (b) decays from $A=117$ residues within 5 s of implantation.

Figure 2

Singles $\gamma$-ray spectra (a) gated on $A=117$ residues and (b) tagged by $\beta$-delayed proton decay from $A=117$ recoils within 5 s of implantation.

Figure 3

Level scheme of ${}^{117}\mathrm{Ba}$ proposed in this work.

Figure 4

Representative coincidence spectra with gates placed on selected transitions in band 1.

Figure 5

Representative coincidence spectra with gates placed on selected transitions in band 2.

Figure 6

Level-spacing systematics for (a) negative- and (b) positive-parity bands in the odd-$A {}^{117-129}\mathrm{Ba}$ isotopes. The energies are normalized to the respective $11/2^{-}(7/2^{+})$ states of negative-parity (positive-parity) bands. The data are from Refs. [8, 9, 17, 18, 35, 36] and the present work.

Figure 7

(a) Extracted alignments and (b) Routhian energies for the ${}^{117}\mathrm{Ba}$ rotational bands.

Figure 8

Calculated quasiparticle Routhians for (a) neutrons and (b) protons as a function of rotational frequency ($\hslash \omega$). The deformations used in the calculations are give in the text. The different line styles represent values of parity and signature, ($\pi , \alpha$), as follows: dashed lines ($-, -1/2$); dot-dashed lines ($-, +1/2$); solid lines ($+, +1/2$); and dotted lines ($+, -1/2$). The lowest neutron and proton Routhians with $\alpha =+1/2$ and $\alpha =-1/2$ are both the $h_{11/2}$ orbitals. The positions of the lowest alignments for neutrons, e.g., EF in panel (a) and protons, e.g., ef in panel (b) are marked by faint vertical dotted lines.