(1) The halogens are a group of chemical elements that includes fluorine, chlorine, bromine, iodine, and astatine .

(2) The total amount of astatine present in the earth's crust, however, is probably less than 1 oz.

(3) This, together with its short lifetime, leaves no reason for considering the effects of astatine on human health.

(4) By one estimate, no more than a millionth of a gram of astatine has ever been produced in the lab.

(5) However, astatine also shows similarities to polonium and bismuth.

(6) There is evidence that astatine behaves like iodine in the body.

(7) The bismuth target is cooled during irradiation to prevent the volatile astatine disappearing.