Tantalum-180m is a very rare primordial isotope and is not in its nuclear ground state. The radioactivity of 180Tam has not yet been observed. Previous attempts to measure the half-life of 180Tam have been performed using various detectors located above ground. In this work a 606 g Ta disk of natural isotopic composition was measured for 170 days in the 225 m deep underground laboratory HADES. The new lower bound for the half life is 1.7·1016 years for electron capture decay and 1.2·1016 years for β--decay. This gives a total lower bound for the half-life of 7.1·1015 years, which is a factor of 6 higher than the previous lower bound.
HULT Mikael;
GASPARRO Joel;
MARISSENS Gerd;
LINDAHL Patric;
WAETJEN Uwe;
JOHNSTON Peter N.;
WAGEMANS Cyriel;
KOEHLER Matthias;
2006-11-28
AMERICAN PHYSICAL SOC
JRC33977
https://publications.jrc.ec.europa.eu/repository/handle/JRC33977,
10.1103/PhysRevC.74.054311,
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