Experimental search for the low-energy nuclear transition in²²⁹Th with undulator radiation

To search for the lowest energy nuclear isomeric transition in ^229 Th in solid samples, a novel adsorption technique which prepares ^229 Th atoms on a surface of CaF _2 is developed. Adsorbed ^229 Th is exposed to highly intensive undulator radiation in the wavelength range between 130 and 320 nm, which includes the indirectly measured nuclear resonance wavelength 160(10) nm. After the excitation, fluorescence from the sample is detected with a VUV sensitive photomultiplier tube. No clear signal relating to the nuclear transition is observed and possible reasons are discussed.