217At

217At, or astatine-217, is a radioactive, synthetic isotope of the halogen element astatine (atomic number 85). It has a mass number of 217 and is not found in nature. As with most heavy astatine isotopes, 217At is highly unstable and exists only briefly under laboratory conditions.

Production and properties: 217At is produced in nuclear reactions in accelerator facilities. Typical production involves bombardment of heavy targets with energetic ions, followed by rapid separation and chemical purification due to the very short half-lives involved. The isotope is part of the occasional series of neutron-deficient astatine isotopes studied to understand nuclear structure near the proton-rich edge of the chart.

Decay modes and half-life: The primary decay mode of 217At is expected to be alpha decay, converting to 213Bi (bismuth-213) and releasing an alpha particle. The half-life of 217At is extremely short and measurements for this isotope are challenging; reported values, when obtainable, place it in the microsecond to millisecond range for certain isomeric states. Other decay pathways are possible in principle, but alpha decay dominates for many heavy astatine isotopes in this mass region.

Applications and significance: Due to its very brief existence, 217At has no practical medical or industrial applications. It is of interest mainly to nuclear physicists studying the structure of heavy, proton-rich nuclei and the mechanisms of heavy-ion fusion-evaporation reactions, as well as the limits of nuclear stability.

See also: astatine isotopes, nuclear data sheets, alpha decay.