Traces of a proton-proton collisions events measured by CERN on May 25, 2011. (AFP/Getty Images/Fabrice Coffrini)
Physicists at the radioactive-beam facility ISOLDE at the European Organization for Nuclear Research (CERN) uncovered the ionization potential of the element astatine, the rarest element in nature, with less than a teaspoon estimated to exist in the Earth’s crust at any given time. Astatine was the last element for which the ionization potential - the energy needed to remove one electron from the atom — remained unknown. Dr. Bruce Marsh of ISOLDE says that studying astatine isotopes is not very different from studying isotopes of other elements, but that the element’s “scarcity in nature makes it difficult to study by experiment, which is why this measurement of one of the fundamental properties is a significant achievement.”
This find is important for practical reasons as well: isotopes of astatine are candidates for radiopharmaceuticals in cancer treatment. Astatine emits (relatively) large alpha particles (made of two protons and two neutrons), which are about 4,000 times bigger than electrons emitted by beta decay, the radiation usually used to treat cancer. Another quality that sets astatine apart from other possible radiopharmaceuticals is its short half-life — about 8 hours (for its most stable isotope). Because of this, any radiotherapy would require hyper-timely delivery methods. In 2007, Rice University researchers found a way to package astatine into DNA-sized tubes of pure carbon for delivery into cancer cells. Rice University researcher Lou Wilson said: “It’s something like the difference between a cannon shell and a BB.”
Now that researchers have figured out the energy required to remove one electron from astatine’s valence shell, they have an insight into the element’s chemical behavior. Experimenting with its various isotopes may pave the way for new cancer radiotherapy that makes a difference for many patients.
