High-spin level structure of ${}^{209}\mathrm{Rn}$

The excited states of ${}^{209}\mathrm{Rn}$ ($Z=86, N=123$) have been populated by the heavy-ion induced fusion evaporation reaction ${}^{198}\mathrm{Pt}({}^{16}\mathrm{O},5n){}^{209}\mathrm{Rn}$ at a beam energy of 102 MeV. The de-excited $\gamma$ rays were detected with the Compton suppressed clover HPGe detectors of the Indian National Gamma Array (INGA) set-up. The high spin spectroscopic study of ${}^{209}\mathrm{Rn}$ has been carried out up to an excitation energy of 7.9 MeV and spin (55/2)$\hslash$. Spin-parity assignments of the excited levels have been determined and are confirmed on the basis of the ratio of directional correlation and polarization asymmetry measurement. The possible presence of new isomeric states has been observed and the half-lives have been estimated. A negative parity sequence of $M1$ transitions has been observed which exhibits the property of magnetic rotation and is interpreted in the framework of semiclassical model calculation. The large basis shell-model calculation has been performed for all the nuclear levels and is found to be in well agreement with the experimental results.

Figure 1

Proposed level scheme of ${}^{209}\mathrm{Rn}$ as derived from the present work. The new $\gamma$ ray transitions, energy levels, and the new assignments of spin-parity, observed in the present work, are indicated in red. The new isomeric state has been indicated in blue.

Figure 2

Plot of (a) $R_{\mathrm{DCO}}$ in a quadrupole gate and (b) ${\mathrm{\Delta }}_{\mathrm{asym}}$ as a function of $\gamma$ ray energies for the new transitions (in red) and already known transitions (in black). The dotted lines in the $y$ axis in (a) are to guide the eye for the DCO ratio corresponding to pure dipole and quadrupole transitions, respectively. The dotted line in the $y$ axis in (b) is to guide the eye for ${\mathrm{\Delta }}_{\mathrm{asym}}$ values corresponding to the electric (positive) and magnetic (negative) nature of the transitions.

Figure 3

Coincidence spectra corresponding to the $\gamma$ ray gates of (a) 668 keV and (b) 731 keV. The new transitions are marked with red, while the transitions marked with an ‘*’ symbol could not be placed in the level scheme.

Figure 4

Coincidence spectrum corresponding to the $\gamma$ ray gates of 316 and 401 keV. The new transitions are marked with red, while lines from the contaminants are marked with a $\#$ symbol and the transitions marked with an * symbol could not be placed.

Figure 5

Coincidence spectrum corresponding to the $\gamma$ ray gate of 1197 keV. The new transitions are marked with red, while those transitions marked with an * symbol could not be placed.

Figure 6

Double coincidence spectra corresponding to the $\gamma$ ray gates of (a) 404 and 718 keV, (b) 325 and 731 keV.

Figure 7

Intensity variation of 140 keV as a function of the coincidence time window at the gates of 316, 401, 404 keV.

Figure 8

Comparison of the experimental data with the shell-model using the KHH7B interaction.

Figure 9

Variation of the effective interaction as the function of shears angle.