Seniority structure of ${}^{136}\mathrm{Xe}_{82}$

The level structure of the $N=82$ nucleus ${}^{136}\mathrm{Xe}$ was studied with the inelastic neutron scattering reaction followed by $\gamma$-ray detection. A number of the spins and parities were reassigned, and many level lifetimes were determined for the first time using the Doppler-shift attenuation method. New shell-model calculations were also performed using both the full $Z=50$–82 model space, and a reduced model space including only the $1d_{5/2}$ and $0g_{7/2}$ orbitals. This new information characterizing ${}^{136}\mathrm{Xe}$ was used to identify the seniority structure of the low-lying levels and to assign ${\left(\pi 0g_{7/2}\right)}_{\upsilon =0}^4$, ${\left(\pi 0g_{7/2}\right)}_{\upsilon =2}^4$, ${\left(\pi 0g_{7/2}\right)}_{\upsilon =4}^4$, $\left(\pi 1d_{5/2}\right){\left(\pi 0g_{7/2}\right)}_{\upsilon =1}^3$, and ${\left(\pi 1d_{5/2}\right)}^2{\left(\pi 0g_{7/2}\right)}_{\upsilon =0}^2$ configurations to describe all observed states below 2.8 MeV.

Figure 1

Data for the determination of the lifetime of the 2634.3 keV level from the Doppler shift of the 1321.2 keV $\gamma$ ray.

Figure 2

Excitation function compared with cindy calculations for various spins for the 2465.1 keV level. The data shown are from the measurements described in Ref. [16].

Figure 3

Angular distribution of the 1246.9 keV $\gamma$ ray from the 2560.0 keV level.

Figure 4

Angular distribution of the 2869.2 keV ground-state $\gamma$ ray from a level of the same energy exhibiting quadrupole character.

Figure 5

Decays of the states with a dominant $\pi 1d_{5/2}{\left(\pi 0g_{7/2}\right)}_{\upsilon =1}^3$ configuration. The arrow widths are representative of the branching ratios of the decays of each level.

Figure 6

Decays of the states with a dominant ${\left(\pi 0g_{7/2}\right)}_{\upsilon =4}^4$ configuration. The arrow widths are representative of the branching ratios of the decays of each level.

Figure 7

The observed levels in ${}^{136}\mathrm{Xe}$ (“EXP”) compared with a two-orbital calculation “$d_{5/2}{g}_{7/2}$” and a full 50–82 shell-model calculation (“SM”). The proposed seniority structure of the levels is indicated on the right: ${\left(\pi 0g_{7/2}\right)}^4$ with $\upsilon =0$, ${\left(\pi 0g_{7/2}\right)}^4$ with $\upsilon =2$, ${\left(\pi 0g_{7/2}\right)}^4$ with $\upsilon =4$, and ${\left(\pi 0g_{7/2}\right)}^3$ with $\upsilon =1$ coupled to $\pi 1d_{5/2}$. Additional levels are indicated in gray.