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A collaborative international research effort spearheaded by the University of Surrey’s Nuclear Physics Group has successfully challenged a long-held belief regarding the shape of the lead-208 (²⁰⁸Pb) atomic nucleus. This significant finding alters foundational assumptions regarding nuclear structure and carries substantial implications for our comprehension of the processes that lead to the formation of heavy elements in the cosmos.
Lead-208 is known for its remarkable stability, classified as a “doubly magic” nucleus and recognized as the heaviest isotope currently identified. Recent research published in Physical Review Letters utilized advanced experimental techniques to probe the nucleus’s shape, revealing that, contrary to the prior assumption of a perfect sphere, lead-208 is actually slightly elongated, taking on a shape akin to that of a rugby ball, also referred to as a prolate spheroid.
Dr. Jack Henderson, the principal investigator of the study from the University of Surrey’s School of Mathematics and Physics, remarked on the significance of the findings:
“We successfully integrated four distinct measurements using the most sensitive experimental apparatus available for this type of investigation. This innovative approach led us to an exciting discovery, showing definitively that lead-208 is not spherical, as one might initially expect. The results pose a direct challenge to existing nuclear theory, paving the way for future research opportunities.”
The research team employed the cutting-edge GRETINA gamma-ray spectrometer at Argonne National Laboratory in Illinois, USA. By bombarding lead atoms with particle beams traveling at 10% of the speed of light—an equivalent speed to circumnavigating the Earth in one second—they generated specific gamma-ray signatures of the excited quantum states within lead-208 nuclei. These interactions provided insights into the actual shape of the nucleus.
The findings have prompted theoretical physicists, including those at the Surrey Nuclear Theory Group, to reassess current models that aim to describe atomic nuclei. The experimental outcomes suggest that the nature of nuclear structure is far more intricate than previously understood.
Professor Paul Stevenson, the primary theorist on the study from the University of Surrey, commented:
“These highly sensitive experiments have illuminated aspects of nuclear physics that we believed were well established, introducing a new challenge in grasping the underlying reasons for our observations. One potential explanation is that the vibrations of the lead-208 nucleus, when excited, may exhibit irregular patterns not previously anticipated. We are now refining our theories to explore the validity of these notions.”
This research, which brought together a diverse group of experts from prominent nuclear physics institutions across Europe and North America, not only questions core principles of nuclear physics but also opens new pathways for exploration in areas such as nuclear stability, astrophysics, and quantum mechanics.
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