Average delayed-neutron energies for 16 isotopes of Br, Rb, I, and Cs have been measured by means of detector ring counting rate ratios in a polyethylene-moderated neutron counter system. An on-line mass spectrometer facility was used to give chemically and mass separated sources of delayed-neutron precursors. A simple expression predicts general trends of the average delayed-neutron energies. Average delayed-neutron energies of individual precursors were weighted by the corresponding delayed-neutron yields and combined to give average energies for all six delayed-neutron groups commonly used in reactor kinetics calculations.

RADIOACTIVITY ${}_{}{}^{87,88,89}{}_{}{}^{}\mathrm{Br}$, ${}_{}{}^{92,93,94,95,96,97}{}_{}{}^{}\mathrm{Rb}$, ${}_{}{}^{137}{}_{}{}^{}\mathrm{I}$, ${}_{}{}^{141,142,143,144,145,146}{}_{}{}^{}\mathrm{Cs}$; measured average delayed-neutron energy; on-line mass separation, polyethylene-moderated neutron counter.

• Received 20 September 1976

DOI:https://doi.org/10.1103/PhysRevC.15.2098