New aspects of the low-energy structure of 211At

Lifetimes of low-energy states in the semimagic nucleus 211At were measured employing the recoil-distance Doppler shift and the Doppler-shift attenuation methods. The deduced transition probabilities are compared to two shell-model calculations, one using the modified Kuo-Herling interaction in a multi-j model space and the other using a semiempirical interaction for protons confined to the single-j 0h9/2 orbital. The Kuo-Herling calculations overestimates some of the ground-state transition probabilities, possibly due to contributions not included in the calculated ground-state wave function of 211At. A strong underestimation of the E2 strengths involving the 7/2-1 state is also observed. Therefore, a modification of a single two-body matrix element of the Kuo-Herling interaction is introduced which improves the agreement with the experimental data significantly. The calculations in the single-j approximation agree very well with the measured transition probabilities, indicating that seniority can be regarded as a good quantum number in 211At.

Automated summary

The lifetimes of low-energy states in the semimagic nucleus 211At were measured and compared to shell-model calculations. It was found that one of the calculations overestimated certain ground-state transition probabilities and underestimated the E2 strengths involving a specific state. However, modifying a matrix element in the calculation improved the agreement with experimental data significantly. The calculations in the single-j approximation showed good agreement with the measured transition probabilities, suggesting that seniority can be considered a good quantum number in 211At.