Astatine

Astatine (symbol At) is a chemical element with atomic number 85. It belongs to the halogen group, which includes fluorine, chlorine, bromine, and iodine. All known isotopes of astatine are radioactive, meaning their atoms decay spontaneously and emit energy and particles.

Astatine is extremely rare in nature. It is produced in small quantities in the decay chains of uranium and thorium, but decays immediately afterward. For this reason, it cannot be collected in significant amounts, and some of its properties are estimated through calculation and comparison with other halogens rather than through direct observation.

Discovery and name

The element was synthesized in the mid-20th century using a cyclotron, a device that accelerates subatomic particles. The name 'astatine' comes from the Greek word meaning 'unstable', referring to the rapid decay of its isotopes. Before its discovery, the position 85 on the periodic table was a gap, and scientists expected it would be filled by a heavy halogen.

Properties

Astatine is considered the heaviest known halogen. Moving down the group, metallic character increases; astatine is therefore seen as more metallic than iodine. It is expected to be a solid with a dark or bluish-black color under normal conditions, but such quantities have never been prepared because the radioactivity it emits generates heat and causes chemical changes.

Medical applications

The isotope At-211 is being investigated for cancer treatment in what is called alpha-targeted therapy. The concept is to attach the isotope to an antibody or targeting molecule designed to bind to cancer cells. The alpha particles it emits release energy over a very short distance, potentially reducing damage to healthy tissue. This research remains in experimental stages, and production of At-211 requires a cyclotron.