Laser life: Astatine inspected

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  • Published: Jul 15, 2013
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Laser life: Astatine inspected

Instantaneous instability

Laser spectroscopy has been used by scientists at CERN and Mainz to investigate the nature of the rare and artificially produced radioactive element astatine for the first time. Credit Nature Commun/Rothe et al

Laser spectroscopy has been used by scientists at CERN and Mainz to investigate the nature of the rare and artificially produced radioactive element astatine for the first time.

The name for element 85, astatine, derives from the Greek word meaning instability because all of its isotopes decay with infamous haste. The most long-lived puts the mayfly to shame with a half life of 8.1 hours, "more here today, gone today" than gone tomorrow, you might say. Its instability means it has been little studied in the laboratory although it sits below iodine in the halogen group of the periodic table so various inferences about its chemistry, should it deign exist long enough to be studied can be made. Nuclear physicists have sighted more than 30 isotopes which are all extremely short-lived.

Great potential

Nevertheless, it has been made synthetically using nuclear reactions - it forms naturally as a decay product of uranium. Now, Mainz-based physicist Sebastian Rothe and colleagues have for the first time explored experimentally one of the element's fundamental physical parameters, its ionization potential. Ionization potential represents binding energy alluding to how easily one can remove an electron from the atom's outer shell, which then determines the chemical bonding characteristics of that element.

The measurements were undertaken at the laboratory of the CERN European Organization for Nuclear Research near Geneva using special lasers developed by the LARISSA (Laser Resonance Ionization for Spectroscopy in Selective Applications) working group at the Institute of Physics at Johannes Gutenberg University Mainz (JGU). Details were published recently online in the journal Nature Communications. "The measurements took place at the ISOLDE radioactive ion beam facility, located at CERN," Rothe told SpectroscopyNOW.

Radiotherapy agents

There is much research into astatine-211 for its potential as a radiotherapy agent for targeting cancer cells. It emits short-range alpha particles when it decays, while its halide properties mean it could be more readily delivered in an injected drug formulation perhaps than other radionuclides. "Astatine is the only halogen we have known absolutely nothing about to date", explains Klaus Wendt, head of the LARISSA working group, Rothe now a CERN Fellow at ISOLDEs Resonance Ionization Laser Ion Source (RILIS) and formerly a graduate student in Wendt's laboratory. LARISSA was originally developed by Mainz physicist Ernst Otten more than three decades ago isotope mass separator ISOLDE at CERN and it is not now the primary technique producing and examining "exotic" radionuclides, involving as it does the use of laser light for the gradual optical excitation of a valence electron of a selected atomic species to the point of ionization.

The measurements carried out by Wendt give an ionization potential for astatine of 9.31751 electron volts (eV). A part of the work, the search for second excited states that bring the electron closer to the IP of the spectroscopy work that led to the precise measurements, performed at CERN, was conducted in collaboration with the research centre for particle and nuclear physics - TRIUMF - in Vancouver, Canada.
Astatine was the last naturally occurring element for which the ionization potential was yet to be measured, Rothe states. "The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of superheavy element 117, the heaviest homologue of astatine," the team concludes. "We are planning to measure the electron affinity of astatine for the first time. Combined with the value for the ionisation potential, this will help us to understand and calculate astatine's chemistry even better," Rothe told us.

Related Links

Nature Commun 2013, 4, 1835: "Measurement of the first ionization potential of astatine by laser ionization spectroscopy"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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