Competing proton and neutron alignments in ^117−120Xe

The 1982 evaluation for A=120 mass chain (1987Ha31) has been revised using experimental decay and reaction data. Adopted values for the level and properties are tabulated and also shown in the drawings. Experimental methods, references, and comments are given in the text.

The level structure of the nucleus ¹²⁸Ce has been investigated via the ¹⁰³Rh(²⁸Si,p2n) reaction at a beam energy of 105 MeV. Six new bands have been found. Spin and parity of levels are assigned based on γ-ray angular distribution and angular correlation measurements. The properties of collective and quasiparticle excitations of ¹²⁸Ce are investigated. A $\text{ν(h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{)}{}^2$ S-band is proposed and the crossing frequency is found similar to that for ¹²⁶Ba. The decoupled and semi-decoupled structures are discussed for the four negative-parity two-quasiproton bands. From an analysis of $\text{(g}{}_{\mathrm{K}}\text{− g}{}_{\mathrm{R}}\text{)}\text{Q}{}_0$ ratios, the $\text{νh}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{(d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{, g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}$ configuration is proposed for a strongly coupled band structure.

Rotational bands built on neutron $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ states are investigated within the Strutinsky mean-field concept. Calculated deformation trajectories of one-, three- and five-quasiparticle configurations are presented. The experimentally observed signature splitting and crossing frequencies in XeBaCe nuclei are compared to theoretical predictions. The systematics of the observed band structures can only be accounted for by allowing a smooth transition from prolate to oblate structure via triaxial shapes as the number of neutrons increases.

Excited states of ¹¹⁷Xe were populated via the reaction ${}^{28}\text{Si +}{}^{92}\text{Mo}$ at 100–120 MeV. More than 40 new γ-transitions and three new positive parity bands have been obverved by means of in-beam γ-ray spectroscopy. The previously known $\text{ν}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ bands were confirmed, and the $\text{ν}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ favored band was extended up to $\text{47}\text{2}{}^{\mathrm{+}}$ in which two bandcrossings have been observed at hω=0.33 and 0.44 MeV, respectively. The band structures have been discussed by means of TRS and CSM calculations. A newly observed rotational band consisting of five γ-transitions has been considered as the $\text{π}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ band of ¹¹⁷Cs.

High-spin structures of the neutron-deficient ^117,118,120Xe isotopes have been studied by in-beam γ-ray spectroscopic techniques. The final nuclei have been identified by means of charged-particle detectors. Collective rotational bands based on the neutron $\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{,}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{and h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ configurations have been identified in ¹¹⁷Xe. In the even ¹¹⁸Xe and ¹²⁰Xe nuclei several new side bands were observed and the previously known bands were extended. The present level schemes include two positive-parity bands constructed to high spin in ¹¹⁸Xe, whereas in ¹²⁰Xe three such bands were observed. In order to explain these bands, both proton and neutron $\text{(}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{)}{}^2$ alignments, as well as the shape degree of freedom, have to be invoked. The possible occurrence of a γS-band is addressed and a pronounced structural change for more heavy Xe-isotopes is discussed. All negative-parity side bands are interpreted in terms of proton two-quasiparticle excitations. The experimental data are compared with total routhian surface calculations.