Physicists are GSI/FAIR accelerator facility gained insight into the structure of the atomic nucleus. Fermium is a synthetic chemical element of the actinide series with atomic number 100. Using laser spectroscopy techniques, they tracked changes in the nucleus’s charge radius and found that it steadily increased as neutrons were added to the nucleus.
Fermium isotopes studied by Warbinek others. It is highlighted in this graph. Image credit: S. Raeder.
“The heaviest atomic nucleus known to date owes its existence to quantum mechanical nuclear shell effects,'' say researchers from the Helmholtz Institute Mainz and Geographical Survey Institute Helmholtzzentrum Schwerionenforschung. said Dr. Sebastian Roeder and colleagues.
“These increase the stability of the nucleus against spontaneous fission, allowing the formation of superheavy nuclei.”
“For a certain number of protons (Z) or neutrons (N), the so-called magic numbers, the nuclear shell exhibits a large energy gap, resulting in increased stability of the nucleus.”
“This is similar to the closed electron shell of noble gases, which provides chemical inertness.”
“The heaviest known atomic nucleus with a magic number for both protons (Z = 82) and neutrons (N = 126) is lead-208, a spherical nucleus.”
“The location of the next spherical gap beyond lead-208 is still unknown. Nuclear models predict it most frequently at Z = 114, Z = 120 or Z = 126, and N = 172 or N = 184. Masu.”
“This variation in predictions is primarily due to the large single-particle density in the heaviest nuclei, among other factors.”
The authors used a laser-based method to investigate a fermium nucleus with 100 protons (Z = 100) and 145 to 157 neutrons (N = 145 to 157).
Specifically, we studied the influence of quantum mechanical shell effects on the size of atomic nuclei.
“This allows us to elucidate the structure of these nuclei in the range around the known shell effect of neutron number 152 from a new perspective,” said Dr. Rader.
“At this neutron number, signs of neutron shell closure were previously observed in trends in nuclear binding energies.”
“The strength of the shell effect was measured by high-precision mass measurements at GSI/FAIR in 2012.”
“According to Einstein, mass equals energy, so these mass measurements gave us a hint about the additional binding energy that shell effects provide.”
“The nucleus around neutron number 152 is shaped more like a rugby ball than a sphere, making it an ideal guinea pig for deeper research.”
“This deformation allows many protons within the nucleus to be separated further apart than in a spherical nucleus.”
In the measurements, the researchers investigated fermium isotopes with lifetimes ranging from a few seconds to 100 days, using different methods for producing fermium isotopes and methodological developments in applied laser spectroscopy techniques. Ta.
Short-lived isotopes are produced at the GSI/FAIR accelerator facility, where in some cases only a few atoms per minute are available for experiments.
The generated nuclei were stopped in argon gas, and electrons were picked up to form neutral atoms, which were then examined using laser light.
The neutron-rich, long-lived fermium isotopes (fermium-255, fermium-257) were produced in picogram quantities at the Oak Ridge National Laboratory in Oak Ridge, USA, and the Laue Langevina Institute in France.
Their results provided insight into the variation of the nuclear charge radius of the fermium isotope over neutron number 152 and showed a stable and uniform increase.
“Our experimental results and interpretation by modern theoretical methods show that in fermium nuclei, nuclear shell effects have a small influence on the charge radius of the nuclei, in contrast to their strong influence on the binding energy of these nuclei. “This shows that,” Dr. Jessica said. Mr. Warbinek is a researcher at CERN.
“This result supports the theoretical prediction that local shell effects due to a small number of neutrons and protons lose influence as the nuclear mass increases.”
“Instead, the effects attributed to the complete assembly of all nucleons dominate, with the nuclei being seen rather as charged liquid droplets.”
of result Published in a magazine nature.
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J. Warbinek others. 2024. Smooth trend of charge radius in fermium and influence of shell effect. nature 634, 1075-1079;doi: 10.1038/s41586-024-08062-z
Source: www.sci.news
