Measurement of the Isolated Nuclear Two-Photon Decay in ^{72}Ge.

Area of Science:

• Nuclear Physics
• Atomic Physics
• Electromagnetic Processes

Background:

• Nuclear two-photon (2γ) decay is a second-order electromagnetic process involving simultaneous emission of two gamma rays from an excited nucleus.
• Measuring 2γ decay rates at low energies, below the electron-positron pair-creation threshold, presents experimental challenges.
• Existing methods may not be sensitive enough for short-lived isomers or low excitation energies.

Purpose of the Study:

• To develop and apply a novel technique for directly measuring nuclear 2γ decay rates in the low-energy regime.
• To determine the 2γ decay half-life of the first-excited 0+ state in bare 72Ge ions.
• To investigate the feasibility of the new technique for isomers with excitation energies down to ~100 keV and half-lives as short as ~10 ms.

Main Methods:

• Combined the isochronous mode of a storage ring with Schottky resonant cavities.
• Developed a new technique enabling direct measurement of 2γ decay rates below the pair-creation threshold.
• Applied the technique to bare 72Ge ions.

Main Results:

• Successfully measured the 2γ decay half-life of the first-excited 0+ state in bare 72Ge ions.
• Determined the half-life to be 23.9(6) ms.
• The measured half-life significantly deviates from theoretical expectations.

Conclusions:

• The newly developed technique is effective for measuring 2γ decay rates of short-lived isomers at low energies.
• The experimental result for 72Ge provides crucial data that challenges current nuclear structure models.
• This method opens new avenues for studying nuclear electromagnetic transitions in various isotopes.