Delayed Neutron Emission in the Decays of Short-Lived Separated Isotopes of Gaseous Fission Products

Delayed-neutron activity of separated isotopes of krypton and xenon and their decay products has been studied. The TRISTAN on-line isotope separator system at the Ames Laboratory Research Reactor was used to provide sources of short-lived gaseous fission products of selected masses, through $A=93\mathrm{}$ for krypton and $A=142\mathrm{}$ for xenon. Total delayed-neutron yields for each mass were measured by a calibrated long counter, and the relative yields of the parent and daughter nuclei in an isobaric decay chain were determined by multiscaling the delayed-neutron activity and resolving the contributions for different half-lives. The precusors and delayed neutron emission probabilities determined in this study are ${\mathrm{Kr}}^{92}$, 0.040%; ${\mathrm{Rb}}^{92}$, 0.012%; ${\mathrm{Kr}}^{93}$, 2.60%; ${\mathrm{Rb}}^{93}$, 1.65%; ${\mathrm{Xe}}^{141}$, 0.054%; ${\mathrm{Cs}}^{141}$, 0.073%; ${\mathrm{Xe}}^{142}$, 0.45%; and ${\mathrm{Cs}}^{142}$, 0.27%. A comparison is made between predictions for delayed-neutron emission from several semiempirical mass formulas and observations for isotopes of As, Br, Kr, Rb, Sb, I, Xe, and Cs.