A study has been made of the radioactive isotopes produced in Cu, Zn, Ga and Ge by bombardment with both fast and slow neutrons. Some of the isotopes were also produced by deuteron bombardment. The results may be summarized in the following table of decay periods.

The writer failed to find the ${\mathrm{Cu}}^{61} (e^{-}T=3.5h)$ suggested by the Michigan group in fast neutron bombardments of copper. No trace of the 23-hr. period reported by Fermi and his collaborators was found in neutron bombardments of gallium.

• Received 3 October 1938

DOI:https://doi.org/10.1103/PhysRev.55.31