Isotope abundance measurement of the half-life of the ββ -decaying nucleus Zr 96 from a 2.68 Gyr zircon sample

The decay half-life of the Zr96 isotope was measured by applying isotope geochemistry techniques to ancient (0.9 and 2.68 Gyr) ZrSiO4 (zircon) samples, with the objective to separate the single and double β-decay branches. The single β decay provides one of the most direct tests for theoretical models describing neutrinoless ββ decays. Both the single and the double β-decay branches lead to the same final nucleus Mo96 and generate an isotopic anomaly over geological time scales. After a chemical separation, the Mo isotopic composition was measured by inductively coupled plasma mass spectrometry (ICPMS). The Mo96 isotopic anomaly was determined in two complete replicate analyses to be 107(40) and 88(20) ppm, which translates to a Zr96 half-life of T1/2=2.03-0.31+0.46×1019yr. With the 2νββ partial decay half-life of the ground-state to ground-state transition known from NEMO-3 to be 2.35±0.21×1019 yr and all other partial ββ-decay half-lives expected to be many orders of magnitude longer, a lower limit for the single-β-decay half-life is set at T1/2β≥6.2×1019 yr.