The $\beta$-decay energies for several mass-separated Xe fission products and their daughters have been measured at the TRISTAN on-line separator facility at the Ames Laboratory research reactor. A well-type plastic scintillator was used in coincidence with a Ge(Li) $\gamma$ detector to determine $\beta$-group end-point energies and deduce $Q$ values. The following $\beta$-decay energies have been determined: ${}_{}{}^{138}{}_{}{}^{}\mathrm{Xe}$, 2.83 ± 0.08 MeV; ${}_{}{}^{138}{}_{}{}^{}\mathrm{Cs}$, 5.29 ± 0.07 MeV; ${}_{}{}^{139}{}_{}{}^{}\mathrm{Xe}$, 4.88 ± 0.06 MeV; ${}_{}{}^{139}{}_{}{}^{}\mathrm{Cs}$, 4.29 ± 0.07 MeV; ${}_{}{}^{140}{}_{}{}^{}\mathrm{Xe}$, 4.06 ± 0.06 MeV; ${}_{}{}^{140}{}_{}{}^{}\mathrm{Cs}$, 5.8 ± 0.1 MeV; ${}_{}{}^{141}{}_{}{}^{}\mathrm{Xe}$, 6.0 ± 0.1 MeV; ${}_{}{}^{141}{}_{}{}^{}\mathrm{Cs}$, 4.98 ± 0.08 MeV; ${}_{}{}^{141}{}_{}{}^{}\mathrm{Ba}$, 3.01 ± 0.06 MeV; ${}_{}{}^{142}{}_{}{}^{}\mathrm{Xe}$, 4.9 ± 0.1 MeV; and ${}_{}{}^{142}{}_{}{}^{}\mathrm{Cs}$, 6.89 ± 0.06 MeV. The decay energies are compared with previous measurements, systematics predictions, and two currently accepted mass relations. The energies are also used to predict the $\beta$-decay energies for seven additional nuclei by means of systematics.

• Received 23 March 1973

DOI:https://doi.org/10.1103/PhysRevC.8.767