A total of 142 $\ensuremath{\gamma}$ rays were observed in the decay of the 45- and 85-sec isomers of $^{136}\mathrm{I}$ using an on-line isotope separator system. Of these, 116 were placed in a level scheme for $^{136}\mathrm{Xe}$ consisting of 50 excited levels up to 6624 keV using results from Ge(Li) $\ensuremath{\gamma}$ singles and $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence measurements. Our results are compared with results from earlier decay and reaction experiments, and the levels below 2.8 MeV are compared with predictions of recent shell-model calculations. Strong $\ensuremath{\beta}$ population was observed to states above 3.5 MeV which are interpreted as neutron particle-hole states.RADIOACTIVITY $^{136}\mathrm{I}$ [from $^{235}\mathrm{U}(n, f)$]; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$-coin, Ge(Li) detectors; $^{136}\mathrm{Xe}$ deduced levels, $J$, $\ensuremath{\pi}$, $log\mathrm{ft}$. Mass-separated $^{136}\mathrm{I}$ activity.

The $\ensuremath{\gamma}$ rays following the $\ensuremath{\beta}$ decay of mass-separated $^{137}\mathrm{Xe}$ to levels in $^{137}\mathrm{Cs}$ have been studied. Of 94 $\ensuremath{\gamma}$ rays observed, 83 were placed in a $^{137}\mathrm{Cs}$ level scheme consisting of 34 excited states up to 3976 keV. The results are compared with levels from single-proton transfer reactions and shell-model calculations.RADIOACTIVITY $^{137}\mathrm{Xe}$ [from $^{235}\mathrm{U}(n, f)$]; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$-coin. Ge(Li) detectors; $^{137}\mathrm{Cs}$ deduced levels, $J$, $\ensuremath{\pi}$, $log\mathrm{ft}$. Mass-separated $^{137}\mathrm{Xe}$ activity.

The $\ensuremath{\gamma}$ rays following the $\ensuremath{\beta}$ decay of mass-separated $^{138}\mathrm{I}$ to levels in $^{138}\mathrm{Xe}$ have been measured using Ge(Li) detectors for both singles and coincidence spectra. A level scheme of $^{138}\mathrm{Xe}$ has been constructed in which eight transitions are placed between levels at 589, 1073, 1464, 1867, 1903, and 2398 keV. The implications of this study are discussed for the systematics of even-even Xe isotopes and $N=84$ isotones.RADIOACTIVITY $^{138}\mathrm{I}$ [from $^{235}\mathrm{U}(n,f)$]; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$-coin. Ge(Li) detectors; $^{138}\mathrm{Xe}$ deduced levels, $J$, $\ensuremath{\pi}$, $log\mathrm{ft}$. Mass-separated $^{138}\mathrm{I}$ activity.

Angular-correlation measurements were made on 12 direct cascades and 5 skip cascades in $^{140}\mathrm{Ba}$. Levels in $^{140}\mathrm{Ba}$ were populated from the 64-sec $\ensuremath{\beta}$ decay of $^{140}\mathrm{Cs}$, which was populated from the decay of mass-separated $^{140}\mathrm{Xe}$. The most intense transitions were measured in coincidence with the first-excited state-to-ground-state transition in even-even $^{140}\mathrm{Ba}$. Definite spin assignments were made for eight levels and tentative spin assignments for five levels. Values are given for the angular-correlation coefficients, and multipolarity mixing ratios are listed where applicable. Systematics for $N=84$ isotones are discussed in light of assignments made for $^{140}\mathrm{Ba}$.RADIOACTIVITY $^{140}\mathrm{Cs}$ (from $^{140}\mathrm{Xe}$ decay); measured $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}(\ensuremath{\theta})$. $^{140}\mathrm{Ba}$ deduced $J$, $\ensuremath{\pi}$. Mass-separated $^{140}\mathrm{Xe}$ activity.

The decays of $^{141}\\mathrm{Xe}$, $^{140}\\mathrm{Xe}$, and $^{136}\\mathrm{I}$ were examined for the presence of energy levels in $^{141}\\mathrm{Cs}$, $^{140}\\mathrm{Cs}$, and $^{136}\\mathrm{Xe}$, respectively, with measurable half-lives in the nsec range. Using a least-squares fitting procedure to analyze the delayed coincidence data taken with a planar Ge(Li)-plastic scintillator system, the half-lives of the following levels were measured: $^{141}\\mathrm{Cs}$: 69.0 keV, 23.3 \\ifmmode\\pm\\else\\textpm\\fi{} 0.7 nsec; 105.9 keV, 8.7 \\ifmmode\\pm\\else\\textpm\\fi{} 0.2 nsec; $^{140}\\mathrm{Cs}$: 13.9 keV, 471 \\ifmmode\\pm\\else\\textpm\\fi{} 51 nsec; 64.7 keV, 3.7 \\ifmmode\\pm\\else\\textpm\\fi{} 0.3 nsec; 103.1 keV, 7.3 \\ifmmode\\pm\\else\\textpm\\fi{} 0.3 nsec (average of two measurements). In addition, upper limits for the half-lives of other levels in these two isotopes are also given, as well as for some levels in $^{136}\\mathrm{Xe}$. Possible multipolarities of the transitions are discussed.RADIOACTIVITY $^{136}\\mathrm{I}$, $^{140}\\mathrm{Xe}$, $^{141}\\mathrm{Xe}$ from $^{235}\\mathrm{U}(n, f)$; measured delayed coin; deduced ${T}_{\\frac{1}{2}}$ for levels in $^{136}\\mathrm{Xe}$, $^{140}\\mathrm{Cs}$, $^{141}\\mathrm{Cs}$; Ge(Li) and scin detectors; mass-separated activities.

Angular correlation measurements have been performed on 12 direct and 4 skip cascades in $^{142}\mathrm{Ce}$, all involving the 641-keV ${2}^{+}$ \ensuremath{\rightarrow} ${0}^{+}$ transition. The $^{142}\mathrm{Ce}$ levels were populated in the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of fission-product $^{142}\mathrm{La}$ produced as a decay product of $^{142}\mathrm{Xe}$ at the TRISTAN on-line isotope-separator facility. Spin-parity assignments or preferences have been made for all 13 excited levels below 3 MeV previously known to be populated in this decay. In addition, a new ${0}^{+}$ level is established at 2030 keV in $^{142}\mathrm{Ce}$. These levels are described in terms of vibrations of a spherical nucleus. An alternate interpretation in terms of quasirotational bands is also presented.RADIOACTIVITY $^{142}\mathrm{La}$(from $^{142}\mathrm{Xe}$ decay); measured $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}(\ensuremath{\theta})$. $^{142}\mathrm{Ce}$ deduced $J$, $\ensuremath{\pi}$. Mass-separated $^{142}\mathrm{La}$ activity.

A seven-detector γ-γ angular-correlation apparatus has been constructed to study short-lived fission product nuclei produced by the TRISTAN on-line isotope separator system. The apparatus employs either seven NaI(Tl) detectors or six NaI(Tl) detectors and one Ge(Li) detector. A 16 384-channel analyzer may be used in conjunction with a series of single-channel discriminators to measure correlations simultaneously on all cascades involving a single γ-ray transition. Alternatively, a buffer tape system may be used to record data simultaneously on all cascades in a decay scheme. The apparatus has been tested on cascades in 138Ba from the decay of 138Cs. The results for three direct and two skip cascades are consistent with the known spins of 2+, 4+, 4+, and 3+ for the levels at 1436, 1899, 2308, and 2446 keV in 138Ba, respectively. In addition mixing ratios of 0.01±0.03, 0.05−0.12+0.20, and 0.10±0.03 have been obtained for the transitions at 1009, 409, and 547 keV in this nucleus.