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Team uncovers fundamental property of astatine, rarest atom on Earth

Posted May 15, 2013
Resonance Ionization Laser Ion Source of ISOLDE

Resonance Ionization Laser Ion Source of ISOLDE

An international team of scientists, including a University of York researcher, has carried out ground-breaking experiments to investigate the atomic structure of astatine (Z=85), the rarest naturally occurring element on Earth.


Astatine (At) is of significant interest as its decay properties make it an ideal short-range radiation source for targeted alpha therapy in cancer treatment.

The results of the project, which was conceived by Professor Andrei Andreyev, an Anniversary Professor in the Department of Physics at the University of York, and Dr Valentine Fedosseev, from CERN, the European laboratory for nuclear physics research in Geneva, are reported in Nature Communications.

Through experiments conducted at the radioactive isotope facility ISOLDE at CERN, scientists have accessed, for the first time, the ionization potential of the astatine atom. This represents the essential quantity defining chemical and physical properties of this exclusively radioactive element.

The successful measurement fills a long-standing gap in Mendeleev’s periodic table, since astatine was the last element present in nature for which this fundamental property was unknown.

As binding energy of the outermost valence electron, the atomic ionization energy is highly relevant for the chemical reactivity of an element and, indirectly, the stability of its chemical bonds in compounds.

Professor Andreyev, who moved to York from the University of the West of Scotland last year, said: “Astatine is of particular interest because its isotopes are interesting candidates for the creation of radiopharmaceuticals for cancer treatment by targeted alpha therapy.

“The experimental value for astatine serves also for benchmarking the theories used to predict the atomic and chemical properties of super-heavy elements, in particular the recently discovered element 117, which is a homologue of astatine.”

Astatine was discovered by D. Corson and co-workers in 1940 by bombarding a bismuth target with alpha particles. The most stable isotope of this element has a half-life time of only 8.1 hours. In 1964, McLaughlin studied a 70 ng sample of artificially produced radioactive isotopes of astatine and was first to observe two spectral lines in the UV region. Apart from this, no other data on astatine’s atomic spectrum was known before the study launched at CERN´s ISOLDE.

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