Isomeric Excitation Energy for ^{99}In^{m} from Mass Spectrometry Reveals Constant Trend Next to Doubly Magic...

Area of Science:

• Nuclear Physics
• Atomic Physics
• Spectroscopy

Background:

• Understanding nuclear structure and stability is crucial for nuclear physics.
• Neutron-deficient isotopes, particularly near closed shells like N=50, present unique challenges for theoretical models.
• Indium isotopes (In) provide a key region for studying these phenomena due to their proximity to the N=50 shell closure.

Purpose of the Study:

• To precisely measure the excitation energy of the 1/2⁻ isomer in Indium-99 (⁹⁹In).
• To significantly reduce the mass uncertainty of the 9/2⁺ ground state of ⁹⁹In.
• To investigate the trend of 1/2⁻ isomer excitation energies in neutron-deficient indium isotopes down to the N=50 shell closure.

Main Methods:

• Utilized the ISOLTRAP mass spectrometer at ISOLDE/CERN for high-precision mass measurements.
• Employed a multireflection time-of-flight mass spectrometer with enhanced resolution.
• Measured the excitation energy of the 1/2⁻ isomer in ⁹⁹In.

Main Results:

• The excitation energy of the 1/2⁻ isomer in ⁹⁹In was determined to be 671(37) keV.
• The mass uncertainty of the 9/2⁺ ground state of ⁹⁹In was substantially reduced.
• Observed an unexpected constancy in 1/2⁻ isomer excitation energies in neutron-deficient indium isotopes approaching the N=50 shell closure.

Conclusions:

• The observed trend challenges the predictive power of current nuclear structure models, including large-scale shell model, ab initio, and density functional theory calculations.
• Theoretical models struggle to accurately reproduce both the isomer excitation energies and ground-state electromagnetic moments across the indium isotopic chain.
• Further theoretical development is needed to explain the persistent isomer energies near the N=50 shell closure.