Double-electron capture on Sn112 to the excited 1871 keV state in Cd112: A possible alternative to double-β decay

We report the first use of a coincidence technique to study neutrinoless double-electron capture (0νECEC) to an excited state in the daughter nucleus. We investigated 0νECEC by Sn112 leading to the possibly degenerate 1871 keV excited state in Cd112 by searching for its deexcitation γ rays of 1253 keV and 618 keV in coincidence. The experiment was performed at ground level. A sample of 3.91 g of tin enriched to 99.5% in Sn112 was placed between two high-purity germanium γ-ray detectors. In order to enhance the sample material, rods of natural tin totaling 1.2 kg (natural abundance 0.97% Sn112) surrounded the cylindrical surface of our two γ-ray detectors. After an exposure of 1.59 kg × days of Sn112, no decays were observed. From this null result we determine a lower limit for the half-life time of T1/2>2.7(1.3)×1019 yr(68%(90%)CL). We hope to achieve a sensitivity in the 1023 to 1024 yr range with a sample of a few kg of Sn112 and improved γ-ray detectors in an underground facility. © 2008 The American Physical Society.

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Author Werner Tornow Physics