The energies of neutron groups selectively activating various elements have been measured by means of the boron absorption method. The elements Rh (3.9 minutes), Rh (44 seconds), Ag (22 seconds), In (13 seconds), In (54 minutes), Ir (19 hours) and Au (2.7 days) exhibit resonance capture for neutrons of energies between one and five volts. The elements Mn (2.5 hours), Cu (5 minutes), As (26 hours), Br (18 minutes), Ag (2.3 minutes), I (25 minutes) Re (20 hours) seem to be activated only by higher energy neutrons (30-85 volts). There are indications that Gd and Sm have resonance groups within the Cd absorption region (thermal energies).

• Received 8 June 1936

DOI:https://doi.org/10.1103/PhysRev.50.328