One of the most important properties influencing the chemical behavior of an element is the electron affinity (EA). Among the remaining elements with unknown EA is astatine, where one of its isotopes, ²¹¹At, is remarkably well suited for targeted radionuclide therapy of cancer. With the At⁻ anion being involved in many aspects of current astatine labeling protocols, the knowledge of the electron affinity of this element is of prime importance. Here we report the measured value of the EA of astatine to be 2.41578(7) eV. This result is compared to state-of-the-art relativistic quantum mechanical calculations that incorporate both the Breit and the quantum electrodynamics (QED) corrections and the electron–electron correlation effects on the highest level that can be currently achieved for many-electron systems. The developed technique of laser-photodetachment spectroscopy of radioisotopes opens the path for future EA measurements of other radioelements such as polonium, and eventually super-heavy elements.

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient $\gamma$ spectrometer MINIBALL. Using ${}^{30}\mathrm{Mg}$ ions accelerated to an energy of $2.25\mathrm{MeV}/u$ together with a thin ${}^{\mathrm{nat}}\mathrm{Ni}$ target, Coulomb excitation of the first excited $2^{+}$ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation $\gamma$-ray yields the $B(E2;0_{\mathrm{gs}}^{+}\to 2_1^{+})$ value of ${}^{30}\mathrm{Mg}$ was determined to be $241(31)e^2{\mathrm{fm}}^4$. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope ${}^{30}\mathrm{Mg}$ resides outside the “island of inversion.”