Astatine

About Astatine

Astatine is the element no one has ever seen as a bulk solid because no one has ever made enough at one time. Every isotope is short-lived; the longest, At-210, runs an 8.1-hour half-life, and a milligram-scale sample would heat itself to vapor through its own alpha emission before you could weigh it. So the entire chemistry of astatine has been worked out at no-carrier-added concentrations — pico- to nanograms in solution — using cyclotron production at the few facilities that can run an internal Bi-209 target with 28 MeV alphas. Berkeley's 60-inch did it first in 1940; Duke, Copenhagen, JRC Karlsruhe, and Texas A&M run targets today. The reason anyone bothers is At-211, a 7.2-hour alpha emitter with a clean decay path that deposits roughly 100 keV per micron over a 60-micron range — about three cell diameters. Conjugate it to an antibody or peptide and you get an alpha-emitting analog of I-131 with damage tightly confined to the targeted cell. Phase I trials in glioma, ovarian carcinoma, and AML have moved At-211 from curiosity to active radiopharmaceutical, with the global production bottleneck now the limiting factor on trial enrollment.