Some of the heaviest atoms in the universe barely exist long enough to be studied, but scientists have now managed to map their inner structure before they vanish.
By firing carefully tuned laser pulses at atoms, a researcher from the University of Gothenburg has shown that the nuclei of neptunium and fermium (radioactive elements in the actinoid series of the periodic table) are not perfectly round but stretched out like rugby balls.
This might seem like a small detail, but nuclear shape influences how atoms behave, how they decay, and how new elements might form. For decades, these kinds of measurements were out of reach because such elements are produced in tiny amounts and decay within seconds.
“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, Mitzi Urquiza, the researcher who performed the laser pulse experiment as a part of her thesis work at the University of Gothenburg, said.
In her research work, Urquiza explained a practical way of studying such elements in detail. Her work opens a new window into the unstable edge of the periodic table, where the heaviest elements exist only briefly before breaking apart.
Catching atoms before they disappear
The biggest hurdle in studying heavy actinides like neptunium is their fleeting existence. These atoms are created in accelerators in extremely small numbers and often survive only for a few seconds.
Traditional techniques require more stable samples and longer observation times, which simply do not exist for these elements. To overcome this, the researchers developed a specialized laser system built around an optical parametric oscillator (OPO).
This system can generate very precise wavelengths of light that conventional lasers struggle to produce, especially in the ultraviolet range, where many heavy elements respond best. More importantly, the setup combines a highly stable continuous-wave laser with pulsed amplification, allowing it to deliver both very precise and high-energy light.
Our “approach enables narrow-linewidth, high-energy pulses with optical linewidths on the order of 100 MHz, covering spectral gaps often inaccessible to conventional Titanium: Sapphire (Ti: Sa) and dye lasers,” the researchers note.
When these laser pulses are directed at the atoms, electrons inside them absorb specific amounts of energy and jump between energy levels.
“As the nucleus is not a point-like charge but possesses a finite volume and shape, these interactions can be observable through small shifts in the energy of an atomic transition known as the hyperfine structure,” the researchers added.
By measuring these tiny effects with high precision, scientists can extract information about the nucleus, including its size, magnetic and electric properties, and shape.
A high-quality description of elusive elements
What makes this approach powerful is the combination of precision and high power. The OPO-based laser produces narrow, high-energy pulses that can probe atoms within their short lifetimes while still resolving very fine details in their energy structure.
The experiments were carried out across several advanced facilities in Europe, each equipped with unique tools needed to produce, isolate, and measure these rare atoms.
By combining data from different setups, the researchers were able to build the first high-quality description of the nuclei of fermium and neptunium, revealing their elongated, rugby ball-like shape.
“These results demonstrate that OPO-based laser systems offer a versatile and efficient solution for extending high-resolution spectroscopy to new regions of the nuclear chart,” the researchers said.
Why nuclear shape matters beyond the lab
Understanding the shape of atomic nuclei is essential for testing and improving models of nuclear physics. These models are used to predict how elements behave, especially those that have not yet been discovered.
The new measurements provide valuable data that can refine these theories and help scientists explore how far the periodic table can extend. “Precise measurements of these observables are essential for testing state-of-the-art theoretical models and exploring the limits of nuclear existence,” the researchers claim.
There are also practical implications. Neptunium is part of the nuclear fuel cycle, so better knowledge of its properties could contribute to managing nuclear waste more effectively.
Moreover, in the longer term, insights from actinide research may also support the production of radioisotopes used in medical treatments such as cancer therapy.
The next step is to improve the laser technology further, expanding the range of wavelengths and increasing stability so that more exotic nuclei can be explored.
You can access the complete thesis from here.