Proton emission is a rare form of radioactive decay in which the nucleus emits a proton, taking a step toward stability. The radioactive decay of atomic nuclei has been a cornerstone of nuclear physics since the inception of nuclear research.
In a groundbreaking experiment, physicists at the University of Jyväskylä have detected the heaviest nucleus ever recorded to decay via proton emission—a rare phenomenon in nuclear physics. The discovery of 188-astatine (188At), an exotic isotope with 85 protons and 103 neutrons, offers fresh insights into the limits of atomic stability.
The newly identified nucleus was produced in a fusion-evaporation reaction, where a natural silver target was bombarded with strontium ions (84Sr). Using the RITU recoil separator, researchers pinpointed this elusive atomic structure despite its short lifespan and low production rate.
Doctoral researcher Henna Kokkonen explains: “Proton emission is an unusual type of radioactive decay, where the nucleus ejects a proton to stabilize itself. Studying such exotic forms of matter is incredibly challenging—but not impossible.”
Theoretical modeling of the 188At nucleus revealed a strongly prolate structure—think of it as watermelon-shaped rather than spherical. Such deformations affect how the nucleus binds its outermost proton, showing an unexpected shift in nuclear stability.
This change in proton binding energy suggests an interaction that has never been observed before in heavy nuclei.
Journal Reference:
- Kokkonen, H., Auranen, K., Siwach, P. et al. New proton emitter 188At implies an interaction unprecedented in heavy nuclei. Nat Commun 16, 4985 (2025). DOI: 10.1038/s41467-025-60259-6
