The decay properties of the fission products ${\mathrm{Ba}}^{141}$ and ${\mathrm{Ba}}^{142}$ have been studied with scintillation techniques. Using a new method, ${\mathrm{Ba}}^{141}$ was obtained free of ${\mathrm{Ba}}^{142}$. The following $\gamma$-ray energies (and relative intensities) were found for ${\mathrm{Ba}}^{141}$: 118 (0.7), 193 (10), 276 (5), 307 (6), 348 (2), 460 (3), 640 (2), 730 (0.7), 860 (0.6), 930 (0.3), 1190 (0.8), 1290 (0.3), 1420 (0.4), and 1650 (0.3) keV. The $\gamma$ rays at 460 and 640 keV are doublets. From single-crystal $\beta$-ray measurements and from $\beta$- and $\gamma$-ray coincidence experiments, the $Q_{\beta }$ value was found to be 3.0±0.1 MeV. There is a weak ground-state transition; the first strong $\beta$-ray group ends at 2.84±0.1 MeV. The combination of all results suggests the following energy levels in ${\mathrm{La}}^{141}$: 193, 307, 470, 650, 930, 1100, 1190, 1290, 1420, and 1650 keV.

The decay of ${\mathrm{Ba}}^{142}$ was studied using mixtures of ${\mathrm{Ba}}^{141}$ and ${\mathrm{Ba}}^{142}$. The following $\gamma$ rays (and relative intensities) were found to be associated with the decay of ${\mathrm{Ba}}^{142}$: 80 (4.5), 135 (2.0), 227 (5.3), 255 (10), 365 (1.3), 425 (2.5), 625 (1.8), 690 (0.9), 905 (4.0) 1070 (2.0), 1180 (5.5), and 1360 (1.2) keV. The $Q_{\beta }$ value is 2.2±0.1 MeV and the strongest $\beta$-ray end point lies in the range 1.65 to 1.85 MeV.

The half-lives of ${\mathrm{Ba}}^{139}$, ${\mathrm{Ba}}^{141}$, ${\mathrm{Ba}}^{142}$, ${\mathrm{La}}^{141}$, and ${\mathrm{La}}^{142}$ have been determined and found to be 82.9±0.2 min, 18±1 min, 11±1 min, 3.90±0.05 h, and 92.5±0.5 min, respectively.

• Received 18 January 1962

DOI:https://doi.org/10.1103/PhysRev.127.1262