Novel Laser Spectroscopy Method to Comprehend Nuclear and Atomic Structure of Radioactive Atoms

Scientists at the University of Jyvaskyla participated in an international association with scientific groups from five countries – Finland, France, Russia, Belgium, and Germany, applying high-resolution laser ionization of radioactive atoms in a supersonic gas jet to probe the properties of hefty elements.

Laser spectroscopy studies have been used for the first time to obtain a thorough comprehension of the atomic and nuclear structure of the short-lived heftiest atoms at the far end of Mendeleev’s periodic table. “The wide majority of the actinide and transactinide elements do not occur in nature and are intricate to produce artificially in weighable quantities,” says Lain Moore, Lecturer at the University of Jyvaskyla.

“Performing spectroscopy of such elements therefore necessitated the development of a novel, highly sensitive and precise method based on laser ionization spectroscopy of radioactive atoms in a gas jet moving at supersonic velocities,” he adds. This novel method has been applied to study the nuclear structure of actinium atoms produced at the LISOL facility in Louvain-la-Neuve, Belgium.

Actinium, with 89 protons, is the foremost and eponymous element of the actinide group. It has just one long-lived isotope limiting our knowledge of the atomic transitions in this element, and hence, making laser spectroscopy experiments highly difficult. At the cyclotron in Louvain-la-Neuve, actinium atoms were produced in a nuclear fusion reaction by bombarding a sleek gold foil with neon nuclei.

The actinium atoms were then stopped in the surrounding argon gas and transported in the cold supersonic jet of a ‘de Laval’ nozzle, a miniaturized version resembling the exhaust of rocket engines, towards a laser interaction zone. In such conditions, resonance laser ionization is employed to ionize the atoms and perform spectroscopy studies. Pure ion beams of actinium are eventually separated according to their mass to gain isotopic selection and are electrostatically guided to a detector array.

“With this novel method, which is usually applicable, the spectral resolution is enhanced by more than an order of magnitude without loss of efficacy, and detailed studies now become possible on nuclei produced at a rate of just one atom every seconds” says KU Leuven researcher Dr. Rafael Ferrer, who head the study.