Identification of ${}^{88}\mathrm{Se}$ and new levels in ${}^{84,86}\mathrm{Se}$

From the analysis of $\gamma \text{−}\gamma \text{−}\gamma$ coincidence data taken with Gammasphere of the prompt γ rays in the spontaneous fission of ${}^{252}\mathrm{Cf}$, the $2^{+}\to 0^{+}$ transition in ${}^{88}\mathrm{Se}$ was identified for the first time. Also, the $4^{+}\to 2^{+}$ and $6^{+}\to 4^{+}$ transitions in ${}^{86}\mathrm{Se}$ were identified along with four new states above $4^{+}$ in ${}^{84}\mathrm{Se}$. Surprisingly, the $2^{+}$ energy rises in ${}^{88}\mathrm{Se}$ compared to ${}^{86}\mathrm{Se}$. This increase in energy could arise from the interaction of a low-lying excited $0^{+}$ state with different deformation and the $0^{+}$ ground state to depress the ground-state energy.

Figure 1

(Color online) Systematics of the $2^{+}$ and $4^{+}$ states in the Se isotopes.

Figure 2

Double gate on 1455.1- and 667.1-keV transitions in ${}^{84}\mathrm{Se}$.

Figure 3

High-energy region of double gates (a) on ${}^{84}\mathrm{Se}$ + (${}^{162}\mathrm{Gd}$) 164.8- and ${}^{84}\mathrm{Se}$ 1415-keV transitions and (b) on ${}^{164}\mathrm{Gd}$ 168.6- and ${}^{84}\mathrm{Se}$ 1415-keV transitions.

Figure 4

Double gates (a) on 164.8- and 253.6-keV transitions in ${}^{162}\mathrm{Gd}$ and (b) on ${}^{162}\mathrm{Gd}$ 164.8- and ${}^{86}\mathrm{Se}$ 863.8-keV transitions.

Figure 5

Double gates (a) on 266.5- and 353.0-keV transitions in ${}^{160}\mathrm{Gd}$ and (b) on 253.6- and 336.2-keV transitions in ${}^{162}\mathrm{Gd}$.

Figure 6

Double gates (a) on 266.5-keV (${}^{160}\mathrm{Gd}$) and 886-keV (${}^{88}\mathrm{Se}$) transitions, (b) on 253.6-keV (${}^{162}\mathrm{Gd}$) and 886-keV (${}^{88}\mathrm{Se}$) transitions, and (c) on 253.6-keV (${}^{162}\mathrm{Gd}$) transition and background. Narrow gates were set on the low-energy transition.

Figure 7

(Color online) Level schemes of ${}^{84,86,88}\mathrm{Se}$ and ${}^{86}\mathrm{Kr}$ [10]. The 3482.2-, 3537.2-, 3702.2-, and 4405.7-keV states in ${}^{86}\mathrm{Se}$, the 1567.9- and 2073.4-keV states in ${}^{86}\mathrm{Se}$, and the 886-keV state in ${}^{88}\mathrm{Se}$ are identified in the present work.