Nuclear physicists measure properties of the rarest element on Earth

Nuclear physicists at the ISOLDE radioactive-beam facility at CERN, including a number from the universities of York and Manchester, have for the first time measured the radioactive properties of astatine, the rarest element on earth.

This new study fills a long-standing gap in the periodic table; astatine, atomic number 85, is the last element present in nature for which this fundamental property remained unknown. The element is of particular interest because isotopes of astatine are candidates for the creation of radiopharmaceuticals for cancer treatment by targeted alpha therapy.

This research, co-funded by the UK’s Science and Technology Facilities Council (STFC) and published today in the journal Nature Communications, could help chemists to develop applications for astatine in radiotherapy, as well as developing theories that predict the structure of super-heavy elements. UK researchers working on the project included Professor Andrei Andreyev from the University of York and Dr Bruce Marsh from CERN and the University of Manchester.

By looking at the ionization potential of astatine, that is the energy needed to remove one electron from the atom and thereby turning it into an ion, this international team of scientists , have been able to understand more about the chemical reactivity of astatine and the stability of its chemical bonds in compounds.

Astatine occurs naturally in only trace amounts on Earth, less than 28 grams (1 oz) exist at any one time, but physicists at ISOLDE can make artificial isotopes of astatine by bombarding uranium targets with high-energy protons. By shining a series of precisely wavelength-tuned lasers at the astatine atoms, the team that operates the resonance ionization laser ion source (RILIS) at ISOLDE measured the ionization potential of astatine to be 9.31751 electron volts.

Dr. Marsh said:

"None of the many short-lived isotopes used in medicine exist in nature; they have to be artificially produced by nuclear reactions. The possible medical isotopes of astatine are not so different in this respect. What is different about astatine is that its 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."

Professor Andreyev noted that:

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

UK access to CERN is funded by STFC.

View the full story at the CERN website at www.cern.ch.

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