Speaker
Description
The structure of the odd-odd, neutron-rich bismuth isotopes provides an excellent testing ground for shell-model calculations. While the low-lying structure in $^{210}$Bi ($Z = 83$, $N = 127$) is expected to be dominated by $(\pi h_{9/2})(\nu g_{9/2})$ configurations, the gradual filling of the $\nu g_{9/2}$ and higher-lying shells will alter this situation. For $^{210,212,214}$Bi, $I^\pi = 1^-$ ground states were suggested [1], while in contrast to this, high-spin [$I^\pi = (6-8^-)$] ground states were proposed for $^{216,218}$Bi [2,3]. Low-lying high-spin [$I^\pi = (8,9^-)$] isomers were observed in $^{210,212}$Bi [1,4,5] and low-spin [$I^\pi = (3^-)$] isomer was suggested in $^{216}$Bi [1]. Moreover, $\beta$ decays of these isotopes allow for investigation of excited levels in polonium isotopes [1-4] and for testing seniority scheme in these nuclei.
In this contribution, an identification of a new $\beta$-decaying state in $^{214}$Bi is discussed. The experiment was carried out at ISOLDE Decay Station (IDS) as a part of a campaign dedicated to decay- and laser-spectroscopy studies of bismuth isotopes performed by our collaboration at ISOLDE-CERN. We investigated $\beta$ decays of $^{214}$Bi and observed strong feeding to high-spin levels in $^{214}$Po, more particularly, to the $8^+_1$ level [6] and states above, which unambiguously proves the existence of a high-spin $\beta$-decaying state in $^{214}$Bi. Half-life of this new state was determined and by using $\gamma$-$\gamma$ coincidences the level scheme of $^{214}$Po was extended. Based on the $\beta$-decay feeding pattern a spin and parity assignment of $I^\pi = (8,9^-)$ is preferred for the new $\beta$-decaying state in $^{214}$Bi.
The existence of two $\beta$-decaying states in $^{214}$Bi completes the chain of low-lying isomers present in odd-odd bismuth isotopes from $^{210}$Bi to $^{216}$Bi. The results will be discussed in connection to systematics in neighboring nuclei and compared with shell-model calculations.
References
[1] ENSDF, Evaluated Nuclear Structure Data File, https://www.nndc.bnl.gov/ensdf
[2] J. Kurpeta et al., Eur. Phys. J. A 7, 49 (2000).
[3] H. De Witte et al., Phys. Rev. C 69, 044305 (2004).
[4] P. A. Baisden et al., Phys. Rev. Lett. 41, 738 (1978).
[5] E. K. Warburton, Phys. Rev. C 44, 261 (1991).
[6] A. Astier and M.-G. Porquet, Phys. Rev. C 83, 014311 (2011).
