First Evidence of Shape Coexistence in the ^{78}Ni Region: Intruder 0_{2}^{+} State in ^{80}Ge

Area of Science:

• Nuclear Physics
• Atomic and Molecular Physics
• Spectroscopy

Background:

• The N=50 shell gap is crucial in understanding nuclear structure near doubly magic nuclei.
• Shape coexistence, where different nuclear shapes exist at similar energies, is a key phenomenon in exotic nuclei.
• Neutron-rich nuclei near doubly magic ^{78}Ni are important for testing nuclear models.

Purpose of the Study:

• To investigate the nuclear structure of the N=48 nucleus ^{80}Ge.
• To search for evidence of shape coexistence in ^{80}Ge.
• To understand the role of nuclear forces in the weakening of the N=50 shell gap.

Main Methods:

• Utilized beta-delayed electron-conversion spectroscopy at the ALTO facility.
• Produced a radioactive ^{80}Ga beam via on-line photofission and isotope separation.
• Measured gamma and electron emission following beta decay of ^{80}Ga.

Main Results:

• Observed an electric monopole (E0) transition for the first time in ^{80}Ge.
• Identified a new intruder 0_{2}^{+} state at 639(1) keV.
• This 0_{2}^{+} state is found to be lower in energy than the first 2_{1}^{+} excited state.

Conclusions:

• The observed intruder 0_{2}^{+} state provides direct evidence for shape coexistence in ^{80}Ge.
• This discovery offers insights into the interplay of monopole and quadrupole forces near Z=32.
• The findings contribute to understanding the evolution of nuclear structure towards the doubly magic ^{78}Ni.