Experimental search for the low-energy nuclear transition in Th-229 with undulator radiation

To search for the lowest energy nuclear isomeric transition in Th-229 in solid samples, a novel adsorption technique which prepares Th-229 atoms on a surface of CaF2 is developed. Adsorbed Th-229 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.