$\beta$-decay study of ${}^{94}\mathrm{Kr}$

$\beta$ decay of neutron-rich nuclide ${}^{94}\mathrm{Kr}$ was reinvestigated by means of a high resolution on-line mass separator and $\beta -\gamma$ spectroscopy. In total 22 $\gamma$-ray transitions were assigned to the decay of ${}^{94}\mathrm{Kr}$, and a new isomeric state was identified. The new information allows us to build detailed levels systematics in a chain of odd-odd rubidium isotopes and draw conclusions on nuclear structure for some of the observed states. The discussed level structure affects the evolution of $\beta$-decay half-lives for neutron-rich selenium, krypton, and strontium isotopes.

Figure 1

Portion of the $\beta$-gated $\gamma$-ray spectrum obtained in the experiment. Transitions identified by energy were assigned to the decay of ${}^{94}\mathrm{Kr}$. Other transitions are marked by parent decay: black circles (${}^{94}\mathrm{Rb}$), gray circles (new lines assigned to decay of ${}^{94}\mathrm{Rb}$), open circles (${}^{94}\mathrm{Rb}\beta n$), black squares (${}^{94}\mathrm{Y}$), crosses for background $\gamma$ rays, and question marks for unassigned transitions.

Figure 2

Background-subtracted $\beta -\gamma -\gamma$ coincidence spectra gated on the following transitions: (a) 167 keV, (b) 293 keV, (c) 402 keV, and (d) 695 keV. The peaks marked with a star ($☆$) are artifacts due to the background-subtraction procedure.

Figure 3

Proposed $\beta$-decay scheme of ${}^{94}\mathrm{Kr}$. Intensities of $\gamma$ transitions (in brackets) are relative to the 629 keV transition. Apparent $\beta$ feedings are calculated from $\gamma$-ray transitions intensities.

Figure 4

Fragment of chart of nuclides around ${}^{94}\mathrm{Rb}$. The spin and parity of the ground state for odd-mass and odd-odd isotopes are shown.

Figure 5

Evolution of low-lying levels in odd-odd rubidium isotopes.

Figure 6

Schematic representation of the energy shifts due to the residual interaction in coupling of the odd-odd particle-particle (closed symbols, dashed line) and particle-hole (open symbols, dotted line) systems. Presented multiplet is $\pi g_{9/2}\otimes \nu g_{7/2}$ but similar parabolas may be created for other orbitals.

Figure 7

(a) Comparison between calculated (full symbols) and experimental (open symbols) half-lives of even-even selenium, krypton and strontium isotopes. (b) Average occupation of the $\nu g_{7/2}$ state calculated with BCS equation.