Research results, Scientific Publications

From the burning of wood to the ways drugs work, the properties and behaviour of matter are governed by the way chemical elements bond with one another. The intricate electronic structures of the atoms that are responsible for chemical bonding are well understood for many of the 118 known elements. But for the superheavy elements lying at the far edge of the periodic table, every measurement presents a major challenge.

In a paper published in Nature Communications https://www.nature.com/articles/s41467-025-64581-x on 3 November 2025, Franziska Maier and her colleagues at CERN’s ISOLDE facility report on the demonstration of a novel technique that promises enormous progress in deciphering the chemistry of (super)heavy elements. The new approach also has potential applications in fundamental physics research and in the development of medical treatments.

Method developed around the use of an ion trap
Superheavy elements are highly unstable and can only be produced in accelerator laboratories in minute amounts. This is why new procedures are first tested on stable elements. The team of researchers at ISOLDE developed a new method based on ion trapping to precisely measure the electron affinity of atoms and molecules.

The electron affinity is the energy released when an electron is added to a neutral atom to form a negatively charged ion, or “anion”. It is one of the most fundamental properties of an element, determining how it forms chemical bonds.

Stable chlorine atoms were used in the demonstration. The new development enabled measurements with a hundred thousand times fewer atoms than in any previous experiment. This opens up the path for electron affinity measurements in superheavy elements.

Conventional electron affinity measurements involve sending anions of the element under investigation through the path of a laser beam. The laser frequency is then tuned to find the exact photon energy above which the extra electron from the anion is removed, which corresponds to the electron affinity of the neutral atom. However, for unstable (super)heavy elements, which are produced at a rate of a few anions per second or less, this single pass of the anions through the laser beam is insufficient to measure the electron affinity.

New method guarantees high measurement accuracy despite fewer anions
To solve this problem, the ISOLDE team trapped chlorine anions in a so-called Multi-Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS). In this trap, the chlorine anions are reflected back and forth between two electrostatic ion mirrors many times like a ping-pong ball, allowing the laser beam to probe the anions during each passage.

“Despite using a hundred thousand times fewer chlorine anions, our novel MIRACLS method reaches the same measurement accuracy as conventional techniques, in which anions pass through the laser beam only once. The improvement lies in the approximately sixty thousand passages of the same ions,” explains lead author of the study, Dr. Franziska Maier. “Our approach uses the trap’s mirrors to ‘recycle’ the anions, opening up a path towards electron affinity measurements in superheavy elements.”

Dr. Franziska Maier carried out the measurements at CERN as part of her doctoral studies in Prof. Dr. Lutz Schweikhard’s working group at the University of Greifswald. He adds that due to relativistic effects in superheavy elements, the increasing number of protons could cause the boundaries between the element groups in the periodic table to fade. “This novel measuring method shall use electron affinities to investigate such effects.”

Many years of experience in the construction and use of electrostatic ion beam traps
The working group from Greifswald has many years of experience in the construction and application of electrostatic ion beam traps. “More than ten years ago, we built a time-of-flight mass spectrometer based on this principle in Greifswald, which was then taken to CERN. It is still being used there for the high-precision determination of the masses of exotic atomic nuclei,” reports Prof. Schweikhard. “A further similar device is used in Greifswald to investigate atomic clusters.” The ion trap that was used for the new experiments in CERN was originally built in Greifswald. It was further developed at CERN and equipped with the lasers required for electron affinity measurements by the international MIRACLS team that is led by Dr. Stephan Malbrunot-Ettenauer.

Potential use in the development of novel cancer therapies
Beyond paving the way for measurements of the elusive electron affinities of superheavy elements, the MIRACLS approach could be applied to rare elements on Earth, including actinium, which, like astatine, is a promising candidate for creating chemical compounds for cancer treatment. It could also be used to measure the electron affinities of molecules, providing data for theoretical calculations that predict their electronic structure. Such calculations are needed for research into antimatter and radioactive molecules, which are gaining increased attention as tools for investigating the fundamental symmetries of nature.

Further information
Publication: Maier, F.M., Leistenschneider, E., Au, M. et al. Enhanced sensitivity for electron affinity measurements of rare elements. Nat Commun 16, 9576 (2025). https://doi.org/10.1038/s41467-025-64581-x
Website of the MIRACLS collaboration at CERN: MIRACLS https://miracls.web.cern.ch/
CERN press release [de] https://home.cern/news/news/physics/ion-recycling-illuminate-heaviest-elements

Current contact details of Dr. Franziska Maier
Dr. Franziska Maier
Facility for Rare Isotope Beams
Michigan State University
640 South Shaw Lane
East Lansing, MI 48824, USA
franziska.maria.maier@cern.ch
maierf@frib.msu.edu
https://www.linkedin.com/in/franziska-maria-maier

Contact at the University of Greifswald
Prof. Dr. Lutz Schweikhard
Institute of Physics
Felix-Hausdorff-Straße 6, 17489 Greifswald
Tel.: +49 3834 420 4750
lschweik@physik.uni-greifswald.de
https://physik.uni-greifswald.de/ag-schweikhard/