229m Th(3/2+, 3.5 eV) and a check of the exponentiality of the decay law

A new object is proposed for checking the exponentiality of the decay law of an isolated metastable state at long times — the anomalously low-lying level 3/2 + (3.5±0.5 eV) in 229 Th. Highly efficient excitation of this level by laser radiation in combination with optimal collection of optical photons emitted in an isomeric transition make it possible to achieve measurement times longer than 50 T 1/2 .