Context:
Researchers at IIT Roorkee have made a breakthrough by detecting and analyzing proton emission from Astatine-188 (¹⁸⁸At), the heaviest known proton-emitting isotope to date. This discovery is significant as it represents the first instance of ground-state proton radioactivity being observed in such a massive isotope.
Key Facts About Astatine (At)
- A scarce and intensely radioactive element belonging to the halogen group (Group 17) in the periodic table.
- Unlike other halogens, Astatine has no stable isotopes.
- It appears as a dark-colored solid at room temperature, but its extreme radioactivity and scarcity make direct study difficult.
- The rarest naturally occurring element on Earth, found only in minute quantities as a transient decay product in uranium and thorium decay chains.
- Chemically akin to iodine but displays more metallic characteristics than other halogens.
- Astatine-188 decays via proton emission, transforming into Polonium-187 (half-life: ~1.4 milliseconds), which further decays into Lead-183 and progresses through additional decay stages until reaching a stable form.
Proton Emission Explained
Proton emission is a radioactive decay process in which an unstable, proton-heavy nucleus expels a proton to achieve greater stability.
- Occurs in nuclei beyond the proton drip line—the threshold where nuclei become too proton-rich to remain stable.
- The proton escapes through quantum tunnelling, a phenomenon where particles penetrate energy barriers that would be insurmountable under classical physics.
Types of Proton Emission:
- Direct Proton Emission: The nucleus ejects a proton directly from its ground state or a low-energy isomeric state.
- Beta-Delayed Proton Emission: Occurs after beta-plus decay, leaving the nucleus in an excited state before proton release.