Alpha-decay from the 3.5 eV isomer of ²²⁹Th

The alpha-decay of a low energy isomer of ²²⁹Th at about 3.5 eV was sought by producing it through the (γ,n) reaction on a ²³⁰Th target. Thorium isotopes in the reaction products were isolated and purified by anion exchange chromatography in a concentrated nitric acid medium to remove lanthanides fission products. The thorium fraction was further purified by samarium fluoride coprecipitation and the precipitate was mounted as a source for α-spectroscopy. Decaying α-signals were observed in the energy region that was expected for ^229mTh, i.e., between 4.83 and 5.08 MeV. The half-life of the decaying component was determined from repeated experiments to be 13.9±3 hours.