By directing pulses of laser light at atoms, researchers can study how radioactive elements decay in a matter of seconds. The method is described in a new thesis from the University of Gothenburg, which shows that the atomic nuclei of the elements neptunium and fermium are shaped like rugby balls.

Actinides are a group of elements at the bottom of the periodic table. They have a high density, are radioactive, and several of them only exist for a few seconds before they decay. Only four of the fourteen elements in this group occur naturally on Earth. The others can be produced in an accelerator, but only in very small quantities. Uranium is the best-known actinide, but a new thesis from the University of Gothenburg focuses on neptunium and fermium.

Difficult to study
“These elements are difficult to study because they are unstable and only exist in extremely small quantities at a time for a very short period of time. At the same time, they could be very useful to us. That is why it is important to try to find out more about the atomic nuclei of actinides and their properties,” says Mitzi Urquiza, doctoral student at the Department of Physics at the University of Gothenburg as part of a collaborative program with Hübner Photonics.
To achieve this, an EU-funded network has brought together 15 researchers from various universities, research institutes, and industry partners. They have developed a new analysis method using a pulsed laser, based on an Optical Parametric Oscillator (OPO). This laser technology can achieve wavelengths and colours that conventional laser systems struggle to produce with sufficient intensity and wavelength precision.
The laser pulses are directed at the atoms, revealing small changes in energy in the wavelengths that are absorbed. These changes provide researchers with information about the size and shape of the atomic nuclei, which is crucial to understanding their properties.

Atomic nuclei like rugby balls
“Thanks to our new method, I was able to produce the first high-quality description of the atomic nuclei of fermium and neptunium. Their nuclei are shaped like rugby balls. The measurements had to be done at several different facilities in Europe, each with unique equipment needed for the study,” says Mitzi Urquiza.
The results of the study can be used to refine theoretical models of atoms and atomic nuclei, making it easier to identify new possible elements and isotopes in future experiments. Neptunium is part of the nuclear fuel cycle, and in the long term, increased knowledge about the element could contribute to progress in reducing nuclear waste, but also in producing radioisotopes used in cancer care.

Thesis: Optical Parametric Oscillators for Spectroscopy of Actinides
Author: Mitzi Urquiza