Al26Decay Scheme

The energies and intensities of the beta and gamma radiations from the long-lived ground level of ${\mathrm{Al}}^{26}$ were studied with scintillation spectrometers. The positron spectrum was obtained using a plastic scintillator with $4\pi$ geometry and was found to have a forbidden shape and an endpoint of 1.160±0.008 Mev. The positrons are in coincidence with a gamma ray with an energy of 1.84±0.01 Mev, which is presumably from the first excited level of ${\mathrm{Mg}}^{26}$. There is also a weak gamma ray with an energy of 1.10±0.05 Mev, in coincidence with the 184-Mev gamma ray, and with an intensity of 0.03 relative to the 1.84-Mev gamma ray. This would be from the second excited level of ${\mathrm{Mg}}^{26}$, to which the ${\mathrm{Al}}^{26}$ decays weakly by electron capture. No other gamma rays are observed. It appears that a peak in the pulse-height spectrum at 700 kev is due to scattering effects rather than a gamma-ray photopeak.