The Excitation of Heavy Nuclei

A new metastable isomer of gold was found. The energy level system of gold has been studied in the region from the threshold to 3.3 Mev. The energy of the metastable state was found to be approximately 250 kev and higher activation levels which combine with the metastable state are found at 1.22±0.03, 1.68, 2.15, 2.56, and 2.97 Mev, respectively. This excitation has also been produced by fast neutrons by the $\mathrm{A}\mathrm{u}-n-n$ reaction and the threshold for this process has been determined. The previously known 43-minute period of mercury has been produced by direct x-ray irradiation as well as a 42-day period in columbium. The strontium activity, known previously from neutron excitation, of 2.7 hours half-life has been produced by both x-ray and electron bombardment of this element.