Evidence for Coexisting Shapes through Lifetime Measurements in ^{98}Zr.

Area of Science:

• Nuclear Physics
• Atomic and Nuclear Chemistry

Background:

• Understanding the evolution of nuclear structure with neutron number is crucial for nuclear astrophysics and models of the atomic nucleus.
• The region around Neutron number (N)=60 in isotopes of Zirconium (Zr) is known for a rapid transition from spherical to deformed shapes.

Purpose of the Study:

• To precisely measure the lifetimes of excited states in ^{98}Zr.
• To investigate the onset of collectivity and nuclear shape coexistence in ^{98}Zr.
• To provide experimental data for theoretical nuclear structure models.

Main Methods:

• Utilized the recoil-distance Doppler shift method at GANIL.
• Populated excited states in ^{98}Zr via a Uranium-238 beam and Beryllium-9 target fission reaction.
• Detected gamma rays with the EXOGAM array and fission fragments with the VAMOS++ spectrometer.

Main Results:

• Measured lifetimes for the 2^{+}, 4^{+}, and 6^{+} states in ^{98}Zr.
• Determined a very small B(E2;2_{1}^{+}→0_{1}^{+}) value, confirming the sudden onset of collectivity at N=60.
• Experimental data compared with Monte Carlo shell model and beyond-mean-field calculations.

Conclusions:

• The results confirm the rapid emergence of nuclear collectivity at N=60 in ^{98}Zr.
• Evidence suggests the coexistence of a spherical ground state with two additional deformed shapes in ^{98}Zr.
• The study provides critical benchmarks for nuclear structure theories in this mass region.