Bound-State Beta Decay of ^{205}Tl^{81+} Ions and the LOREX Project

Area of Science:

• Nuclear Physics
• Particle Astrophysics
• Geochemistry

Background:

• Stable Thallium-205 (Tl) ions possess the lowest energy threshold for capturing electron neutrinos (νe), making them crucial for solar neutrino detection.
• The proposed Lorandite Experiment (LOREX) aimed to measure the long-term solar neutrino flux using natural lorandite ores.
• Determining the electron neutrino capture cross-section requires precise knowledge of the weak transition strength between Tl-205 ground and excited states in Pb-205.

Purpose of the Study:

• To experimentally determine the strength of the weak transition between the ground state of Tl-205 and the 2.3 keV first excited state in Pb-205.
• To measure the half-life of the bound-state beta decay (βb) of fully ionized Tl-205 (Tl-205^81+) ions, a critical parameter for the LOREX experiment.
• To assess the feasibility of the LOREX experiment in light of the measured decay properties.

Main Methods:

• Utilizing the Experimental Storage Ring (ESR) at GSI, Darmstadt, for precise measurements.
• Performing measurements on fully ionized Tl-205^81+ ions to study bound-state beta decay (βb).
• Measuring the half-life of the βb decay of Tl-205^81+.

Main Results:

• The half-life of the βb decay of Tl-205^81+ was measured to be 291 days (with uncertainties +33/-27 days).
• This measured half-life is significantly longer than previously predicted by theoretical models.
• The extended half-life implies a reduced signal-to-noise ratio for the LOREX experiment.

Conclusions:

• The experimental determination of the Tl-205^81+ βb decay half-life provides crucial data for neutrino physics.
• The measured half-life challenges the original feasibility projections for the Lorandite Experiment (LOREX).
• Further research may be needed to refine solar neutrino detection strategies or explore alternative methods.