Search for the “missing” α-decay branch in 239Cm

A search for the α-decay of 239Cm was carried out via the fusion reaction 232Th(12C,5n) 239Cm at GSI, applying nuclear chemistry techniques. The 239Cm α-decay would provide a link between known nuclear masses and α-decay energies measured in the region of the superheavy elements. Three different 12C beam energies were chosen in the present experiments. The α peaks of 238,240Cm were observed clearly at a 12C energy of 74 MeV, while 238Cm disappeared at 70 MeV to provide an undisturbed α-spectrum for a sensitive search of 239Cm decay. No α-events between 6.34 and 6.50 MeV, which could be assigned to 239Cm with confidence, were observed in this experiment. The upper limit of the α-branch of 239Cm was less than 1.0×10−5.