Decay of the low-energy nuclear isomer Th-229(m)(3/2(+),3.5 +/- 1.0 eV) insolids (dielectrics and metals): A new scheme of experimental research - art. no. 064308

The decay channels and the half-life of the proposed anomalously low-energy nuclear isomer Th-229(m)(3/2(+),3.5+/-1.0 eV) in a dielectric and in metal s are discussed. The preferred decay channel in wide energy-gap dielectrics is via nuclear gamma emission in the optical range. The isomer's half-life lies in the range 10 min-1 h in (ThO2)-Th-229 for the spectral range N-ome ga=4.5-2.5 eV. Nonradiative decay channels dominate in metals. A two-step e xperimental scheme is developed. The first step is the excitation of the lo w-energy isomeric level by synchrotron radiation via the 29- and 72-keV lev els, and precise measurement of the wave length of the low-energy nuclear t ransition in (ThO2)-Th-229. The second step is the excitation of a large nu mber of the isomeric nuclei Th-229(m)(3/2(+),3.5+/-1.0 eV) from the ground state by laser radiation in thorium dioxide, and investigation of the alpha decay of the isomeric level.