Астат

radioactive crystal(s) halogen with 20 isotopes; heaviest of the halogens; 209At, t1/2=5.5 h; 210At, t1/2=8.3 h; more metallic than iodine; preparation: from Bi by α-particle bombardment; possible medical uses, concentrates in thyroid gland [HAW93] [MER06]

Physical properties of this element have not been well investigated due to short half-lives of isotopes. The element is volatile; may be distilled in vacuum at room temperature in a glass apparatus; and condensed in a dry ice trap. It is soluble in chloroform, ether, hexane and many other organic solvents. Solubility in water should be of low order.

Astatine is one of the rarest elements in nature. Extremely small amounts of short-lived isotopes At-215, At-217, At-218 and At-219 are naturally found occurring in equilibrium with uranium, neptunium and thorium isotopes. The element was named by Corson, MacKenzie and Segre who produced the first of its isotope At-211 in 1940 by bombarding bismuth with alpha particles. Since then many isotopes in the mass range 200 to 219 have been synthesized. All isotopes, however, are unstable, their half-lives ranging between a few microseconds to less than ten hours. The most stable ones are At-210, At-211 and At-209. No use of this element is known so far.

Exposure to radiation may cause cancer. Studies on experimental animals show it induces tumors.