Search for the decay of 229mTh by photon detection

A search for the isomeric transition of 2 2 9 m Th at 3.5 eV was made by photon detection with a low-noise photomultiplier for samples prepared by a rapid chemical separation from the parent nuclide 2 3 3 U by means of ananion exchange method. The photon emission caused by the disintegration of 2 2 9 m Th was not observed for 2 2 9 Th nitric acid solution samples. From the experimental results, the limits of the half-life of 2 2 9 m 'Th as dissolved in HNO 3 solution are discussed.