DISINTEGRATION SCHEME OF LONG-LIVED ALUMINUM-26

The disintegration scheme of the long-lived groundstate isomer of Al/sup 26/ was determined. The maximum positron energy as determined by absorption measurements is 1.16 sintering time 0.05 Mev; this agrees with the expected 1.17 Mev. The spectrum appears to be simple. The scintillation gamma spectrum shows intense positron annihilation radiation, a strong peak at 1.85 sintering time 0.03 Mev, and weak peaks at 1.12 sintering time 0.03 Mev and 2.96 sintering time 0.05 Mev, corresponding to transitions from the known Mg/sup 26/ states at 1.82 and 2.97 Mev. A peak at 0.68 Mev is from the addition of two annihilation photons, one being backscattered from the source and surroundings; the gamma of ~0.7-Mev energy reported by others is not present. The peak at 2.97 Mev is shown to result from 2.97-Mev photons as well as from addition of 1.82- and 1.15-Mev photons. The relative intensities of the annihilation and gamma radiations indicate that Al/sup 26/ undergoes (84.6 sintering time 1.8)% positron emission to the 1.82-Mev state of Mg/sup 26/; (11.4 sintering time 1.9)% electron capture to the same state; (3.7 sintering time 0.3)% electron captare to the 2.97-Mev state followed by emission of 1.15- and 1.82-Mev gamma- rays; and (0.30more » sintering time 0.03)% electron capture to the same state followed by 2.97-Mev radiation. Other energetically possible transitions are apparently negligible in intensity. Auger electrons and x-rays were observed in a proportional counter spectrometer. Analysis of the spectra yielded K-shell fluorescence yields of 0.008 sintering time 0.003 for magnesium and 0.008 sintering time 0.003 for aluminum. (auth)« less