[en] The decay of low energy isomeric state of ²²⁹Th was explored applying a novel radiochemical technique to the (γ, xn) reaction products on ²³⁰Th target. The decaying α-emitter was observed between 4.687 MeV α-peak of ²³⁰Th and the α-peaks of the (γ, 2n) product ²²⁸Th. The energy of the decaying component is consistent with the expected energy for the α-particles from ^229mTh. The half-life of the decaying component was determined to be 13.9±3 hours. It seems that the present determination of the half-life is the longest value for ^229mTh, because fluoride has no valence electrons that undergo electronic bridge interaction with the thorium nucleus. (author)