The building blocks of the universe are atoms. Research into the structure of the atomic nucleus is critical for advancements in astrophysics, medical imaging, and data storage.
A new study by Department of Physics researchers at Florida State University's John D. Fox Superconducting Linear Accelerator Laboratory investigated titanium-50 nuclei. The findings indicate that a long-held explanation for the origin of magnetism in atomic nuclei may not fully apply to titanium-50.
Published in Physical Review Letters, the research suggests a potential need to revise current understandings of nuclear magnetism.
Associate Professor Mark Spieker, a co-author, stated that current models propose magnetic strength is largely generated by spin-flip excitations, which occur when protons or neutrons change their spin orientation between spin-orbit partner orbitals. The study's authors report that this type of spin-flip may not be the sole mechanism responsible for generating nuclear magnetism.
Background on Nuclear Models
Current nuclear models treat protons and neutrons as individual particles occupying fixed energy levels. A spin-flip happens when these particles alter their spin orientation as they move between energy levels, which is believed to generate magnetic strength. For many years, this spin-flip mechanism was considered the primary cause of magnetic signals in atomic nuclei, a behavior also predicted by advanced computer modeling.
Experimental Findings
The experiments conducted at Florida State University revealed that nuclear excited states clearly exhibiting neutron spin-flip structure were not the ones producing the strongest magnetic signals.
This observation implies that an increase in neutron "spin-flip" structure did not automatically result in a stronger magnetic effect.
Methodology
Researchers performed a neutron-transfer experiment at the John D. Fox Superconducting Linear Accelerator Laboratory. They used the facility's Tandem Van de Graaff Accelerator to direct a deuteron beam (a nucleus composed of a proton and a neutron) at a thin foil of titanium-49. During the reaction, a neutron from the beam transferred to titanium-49, forming titanium-50 and leaving a residual proton.
The Super-Enge Split-Pole Spectrograph at the Fox Lab measured the various angles at which the proton was emitted, allowing for analysis of the neutron transfer to titanium-49. Spieker explained that the process allows measurement of the excitation energy given to the nucleus.
The FSU team combined their results with previously published electron- and proton-scattering data, alongside new photon-scattering experiments from collaborating universities. This comprehensive approach allowed a detailed examination of how neutrons flip their spin and their contribution to the nucleus's overall magnetic behavior.
The magnetic signal observed in the experiments did not match the strength predicted by existing models, suggesting additional factors contribute to the measured magnetic signals in titanium-50.
Graduate student Bryan Kelly, a study co-author, noted that combining these datasets was crucial to concluding that the spin-flip mechanism between spin-orbit partners is not the only factor in magnetic strength generation.
Implications and Future Research
The study's findings challenge long-standing assumptions concerning the magnetic behavior of nuclei. Improved understanding of atomic nucleus structure could lead to refinements in current models used in nuclear physics and astrophysics, potentially linking them with high-energy physics models. Such interdisciplinary efforts aim to enhance the understanding of fundamental matter.
Spieker emphasized that a better understanding of the universe offers new insights that could be applied to benefit society and drive progress, as atomic nuclei are the building blocks of all ordinary matter.
Future studies will investigate the source of the unexplained magnetism in titanium-50. Kelly indicated that further investigations are needed to understand why magnetic strength is distributed across several nuclear states.
Acknowledgements
Contributing researchers were from Florida State University, the Technical University of Darmstadt in Germany, and the Triangle Universities Nuclear Laboratory in North Carolina at Duke University.
The research received support from the U.S. National Science Foundation, the U.S. Department of Energy Office of Science, the German Research Foundation, the Institute of Atomic Physics in Romania, the Romanian Ministry of Research, and the Romanian Government.