The beta spectra and gamma rays of the isotopes ${\mathrm{Tm}}^{170}$, ${\mathrm{Pr}}^{142}$, and ${\mathrm{Rb}}^{86}$ have been examined with various types of spectrometers. An intermediate-image beta-ray spectrometer with a 10 percent transmission and a 5.5 percent resolution was used to examine the total and coincidence beta spectra. Total beta spectra were also studied with a thin-lens spectrometer set to about two percent resolution. Gamma rays were also studied with a scintillation spectrometer.

The results of the investigation indicate that the 125-day activity of ${\mathrm{Tm}}^{170}$ has two beta groups with maximum energies of 970±2 kev and 886±9 kev. Their respective intensities are about 78 percent and 22 percent, and their respective $log\mathrm{ft}$ values are approximately 9.0 and 9.1. Both beta groups are assigned as first forbidden transitions with $\Delta I=\pm 1$, "yes." The single observed gamma ray of ${\mathrm{Tm}}^{170}$ is assigned as an $E2\mathrm{}$ transition with an energy of 84.1±0.4 kev.

The 19.2-hr activity of ${\mathrm{Pr}}^{142}$ has two beta groups with maximum energies of 2166±6 kev and 586±15 kev. The 2166-kev beta group has a $log\mathrm{ft}$ value of about 7.8 and the 586-kev beta group has a $log\mathrm{ft}$ value of about 7.1. The $log\left[\right(W{o}^2-1\left)ft\right]$ value of the 2166-kev beta group is 10.2. The intensities for the 2166-kev and 586-kev beta groups were found to be, respectively, 90-95 percent and 5-10 percent.

The 2166-kev beta group is assigned as first forbidden with $\Delta I=2\mathrm{}$, "yes" and the 586-kev beta group as first forbidden with $\Delta I=0\mathrm{} or\pm 1$, "yes." The single observed gamma ray, having an energy of 1572±8 kev, is tentatively assigned as an $E2\mathrm{}$ or $M1\mathrm{}$ transition. The $E2\mathrm{}$ and $\Delta I=0\mathrm{}$, "yes" choices are probably correct.

The 19.5-day activity of ${\mathrm{Rb}}^{86}$ has two beta groups with maximum energies of 1770±4 kev and 680±6 kev. Their intensities are about 88 percent and 12 percent, respectively. The $log\mathrm{ft}$ value for the 1770-kev beta group is about 8.5 and for the 680-kev beta group 7.8. The $log\left[\right(W{o}^2-1\left)ft\right]$ value for the 1770-kev beta group is 9.7. This beta group is assigned as a first forbidden transition with $\Delta I=2\mathrm{}$, "yes," and the 680-kev beta group is tentatively assigned as first forbidden with $\Delta I=0\mathrm{}$, "yes." The single gamma ray has an energy of 1080±6 kev and is tentatively assigned as an $E2\mathrm{}$ transition.

The Kurie plots of the 680-kev beta group of ${\mathrm{Rb}}^{86}$ and the 886-kev beta group of ${\mathrm{Tm}}^{170}$ were examined for deviations from a straight line. Within experimental error no deviation from a straight line was observed.

• Received 21 April 1954

DOI:https://doi.org/10.1103/PhysRev.95.1523