For the first time, scientists have acquired direct evidence of rare, pulsing pear-shaped structures within atomic nuclei of the rare-earth element Gadolinium, thanks to new research led by the University of Surrey, the National Physical Laboratory (NPL) and the IFIN-HH research institute in Bucharest, Romania.

The study, published in Physical Review Letters, provides definitive proof of a strong collective ‘octupole excitation’ in the nucleus of Gadolinium-150, a long-lived radioactive isotope of this rare-earth element, which is used in applications such as superconductors, nuclear power operations and MRI contrast materials.

The experimental signature is interpreted as the protons and neutrons inside the atomic nucleus vibrating in a coordinated pattern, resulting in a pulsing, asymmetric, pear-shaped structure.

Professor Patrick Regan, NPL professor of Nuclear Metrology at the University of Surrey and co-lead on the study, said:

"It’s so very cool to be able to ‘see’ the shapes of these smallest quantum objects. These unique, precision measurements obtained by our collaboration enable a deeper understanding of how the constituent building blocks of matter combine to allow coherent quantum collective structures and shapes to emerge in atomic nuclei. Such measurements also provide the most stringent tests of our best current models to explain how hadronic matter interacts at the sub-atomic level."

Using high-precision gamma-ray measurements of emissions from the nucleus of Gadolinium-150, the researchers were able to observe the signature fingerprints of these incredibly tiny pear-shaped structures. Atomic nuclei are so small that even the most advanced optical microscopes are unable to detect them, but information on their structure can be obtained by measuring the characteristic (gamma-ray) emissions as they relax.

The findings open a new window into the quantum world, providing what can be described as a ‘femtoscope’ – a high-precision ‘nuclear microscope’ – that allows scientists to look deep into the subatomic structures that shape our universe.

The results also represent a unique challenge to current theoretical models, which struggle to explain how these shapes can arise from complex interactions of the protons and neutrons which make up the Gadolinium-150 nucleus.

Dr Esra Yuksel, lead theoretician on the paper from the University of Surrey, said:

“The published results of these extremely sensitive measurements of quantum decays allow us to stress-test our best current theoretical understanding of how protons and neutrons arrange themselves within the atomic nucleus.

“The resulting octupole collectively – or ‘pear-shaped’ signature – is amongst the largest identified to date. This allowed us to test five different state-of-the-art theoretical models to pinpoint the best one. Our calculations offer valuable insights into the current understanding of how such unusual nuclear shapes form in these fascinating quantum laboratories.”

The research involved an international collaboration of 12 institutions from the UK, Romania, India, Japan, China and the Czech Republic.

The National Physical Laboratory is the UK’s National Metrology Institute and is responsible for traceability of all radioactivity measurements in the UK to the SI unit of the becquerel (Bq).

[ENDS]