High-Resolution Laser Spectroscopy on the Hyperfine Structure of ^{255}Fm (Z=100).

Area of Science:

• Nuclear Physics
• Atomic Physics
• Spectroscopy

Background:

• Fermium-255 (²⁵⁵Fm) is a heavy actinide nuclide produced via reactor breeding.
• Understanding the properties of heavy, short-lived nuclides is crucial for nuclear structure models.

Purpose of the Study:

• To precisely determine the nuclear magnetic dipole (μ) and electric quadrupole (Q ) moments of ²⁵⁵Fm.
• To provide a stringent benchmark for atomic and nuclear theoretical calculations.
• To establish ²⁵⁵Fm as a reference isotope for future spectroscopic studies.

Main Methods:

• High-resolution in-source laser spectroscopy was performed at the RISIKO mass separator.
• The perpendicularly illuminated laser ion source and trap (PI-LIST) was utilized.
• Experimental hyperfine structure data were combined with atomic ab initio calculations (multiconfiguration Dirac-Hartree-Fock).

Main Results:

• The nuclear magnetic dipole moment was determined to be μ = -0.75(5) μ .
• The electric quadrupole moment was determined to be Q = +5.84(13) eb.
• The results indicate occupation of the ν7/2[613] Nilsson orbital and stable prolate deformation.

Conclusions:

• The derived nuclear moments agree well with theoretical predictions, validating nuclear models.
• The findings revise previous experimental data for ²⁵⁵Fm.
• ²⁵⁵Fm is confirmed as a valuable reference isotope for advanced spectroscopic investigations.