First observation of high-spin states in ${}^{214}\mathrm{Po}$: Probing the valence space beyond ${}^{208}\mathrm{Pb}$

Excited states in ${}^{214}\mathrm{Po}$ have been populated using the ${}^{18}\mathrm{O}$ $+$ ${}^{208}\mathrm{Pb}$ reaction at 85-MeV beam energy and studied with the Euroball IV $\gamma$-multidetector array. The level scheme has been built up to $~2.7$-MeV excitation energy and spin $I=12\hslash$ from the triple-$\gamma$ coincidence data. Spin and parity values of most of the observed states have been assigned from the $\gamma$-angular properties. The configurations of the yrast states are discussed using results of empirical shell-model calculations and by analogy with the neighboring nuclei. The ${}^{214}\mathrm{Po}$ level scheme established in this work constitutes an important step for the determination of the effective nucleon-nucleon interactions beyond $N=126$.

Figure 1

Spectra of $\gamma$ rays in double coincidence with (a) the first transition of  ${}^{214}\mathrm{Po}$ (609 keV) and the $K$${}_{\alpha 1}$ x ray of Po, (b) the 405- and 324-keV transitions, and (c) the 324- and 244-keV transitions. The lines, marked with a star, are contaminants due to several Rh isotopes (see text).

Figure 2

Level scheme of  ${}^{214}\mathrm{Po}$ determined in this work. The half-life of the $8_1^{+}$ state is 13(1) ns (see text). The width of the arrows is representative of the intensity of the $\gamma$ rays.

Figure 3

Angular distribution of the most intense transitions of ${}^{214}\mathrm{Po}$ produced in the ${}^{18}\mathrm{O}$ $+$ ${}^{208}\mathrm{Pb}$ reaction. Solid (red) lines are the fits using the standard Legendre polynomials (results are given in Table ).

Figure 4

Low-energy part of the $\gamma$-ray spectra showing the yrast transitions of ${}^{214}\mathrm{Po}$ detected at a mean angle of $39.3^{°}$ by the tapered and cluster detectors (a) and at a mean angle of $76.6^{°}$ by the clover detectors (b).

Figure 5

Spectra of $\gamma$ rays in double coincidence with (a) the 554- and 405-keV transitions and (b) the 554-keV transition and the $K$${}_{\alpha 1}$ x ray of Po.

Figure 6

Time distributions between the emissions of $\gamma$ rays of $\gamma$Po showing either prompt coincidences [curves in red and green, panel (a)] or delayed ones corresponding to the decay of the 1583-keV state [curves in blue, panels (b), (c), and (d)]. They are compared with an example of $\gamma$ rays of ${}^{212}\mathrm{Po}$ in prompt coincidences, shown with the curve filled in gray (see text).

Figure 7

Energies for expected states in ${}^{214}\mathrm{Po}$, (i) from the $(\nu g_{9/2}){}^4$ configuration calculated using empirical SM (red full circles), (ii) from the $(\nu g_{9/2}){}^1$$(\nu i_{11/2}){}^1$ configuration measured in ${}^{210}\mathrm{Pb}$ (stars in magenta), (iii) from the $(\pi h_{9/2}){}^2$ configuration measured in ${}^{210}\mathrm{Po}$ (blue filled diamonds), (iv) from the $(\pi h_{9/2}){}^1(\pi f_{7/2}){}^1$ configuration measured in ${}^{210}\mathrm{Po}$ (violet filled square). The experimental states of ${}^{212}\mathrm{Pb}$ are shown for comparison (red empty circles).

Figure 8

Bottom: Evolution of the first energy levels in the even Po isotopes, ${}^{210-218}\mathrm{Po}$, and in ${}^{210}\mathrm{Pb}$. The energies of the $8_1^{+}$ states are adjusted to a constant value (see text). Top: Experimental values of the reduced transition probabilities $B(E2;8^{+}\to 6^{+})$ for ${}^{210}\mathrm{Pb}$, ${}^{210}\mathrm{Po}$, and ${}^{212,214}\mathrm{Po}$. Data are taken from Refs. [1, 2, 3, 5, 6] and this work.