Discovery of Astatine-188 Sheds New Light on Nuclear Physics

In June 2025, researchers at the University of Jyväskylä's Accelerator Laboratory in Finland identified astatine-188 (188At), the heaviest known nucleus to undergo proton emission. This discovery provides new insights into nuclear structure and stability, challenging existing theoretical models.

The team produced 188At by bombarding a natural silver target with strontium-84 (84Sr) ions, resulting in a fusion-evaporation reaction that formed the new isotope. The identification was achieved using the RITU recoil separator, a device designed to separate and detect rare nuclear reaction products. The isotope consists of 85 protons and 103 neutrons, making it the lightest known isotope of astatine.

Proton emission is a rare form of radioactive decay where an unstable nucleus emits a proton to achieve a more stable state. The discovery of 188At marks the first observation of proton emission in such a heavy nucleus, expanding our understanding of nuclear decay processes. Theoretical modeling indicates that 188At has a highly deformed, prolate (elongated) shape, often described as "watermelon-shaped." Notably, the proton emission from this nucleus exhibited an unexpected deviation in binding energy, suggesting the presence of a previously unobserved interaction in heavy nuclei.

The last significant discovery of a proton-emitting nucleus occurred in 1996 with bismuth-185. The identification of 188At represents the first such discovery in nearly three decades, highlighting advancements in experimental techniques and theoretical modeling. This discovery challenges existing nuclear models and provides a new benchmark for testing theoretical predictions. Understanding the properties of 188At and similar nuclei can enhance our knowledge of nuclear forces and the limits of nuclear stability. Future research may focus on observing more decay events of 188At to refine measurements of its decay energy and half-life. Additionally, studying the decay of the yet-to-be-discovered 189At could provide further insights into proton emission and nuclear structure.

The University of Jyväskylä's Accelerator Laboratory is a leading research center specializing in nuclear and accelerator-based physics. It provides advanced infrastructure for studying rare nuclear phenomena. Astatine is the rarest naturally occurring element in Earth's crust, with all its isotopes being short-lived. The most stable isotope, astatine-210, has a half-life of approximately 8.1 hours.

The identification of 188At not only marks a significant milestone in nuclear physics but also opens new avenues for exploring the fundamental forces that govern atomic nuclei. As researchers continue to investigate these rare decay processes, our understanding of the universe's building blocks will deepen, potentially leading to advancements in various scientific and technological fields.