LXXV. The natural radioactivity of lutetium

The radiations from the decay of naturally occurring 178Lu are studied in detail. The β --spectrum, which was found to be of allowed shape, was investigated using internally mounted sources of thickness 0·149 mg/cm2 and 0·149 mg/cm2 in a well-shielded proportional tube spectrometer. A half-life of 4·56 ±0·3 × 1010 years was obtained for the β-transition with a maximum energy of 425±15 kev and the log ft value, 18·75, suggests a 3rd or 4th forbidden transition. Strong electron peaks arising from the internal conversion of an 89kev γ-ray were observed and a K-capture branching ratio of 3 ± 1 % is derived from a study of the intensity and nature of the L x-rays accompanying the disintegrations. NaI scintillation counters were used for the measurement of γ-rays of energy 3l0 ± 10 kev and 190 ± 10 kev and the evaluation of their internal conversion coefficients classifies them as E.Q. transitions. The intensities of the γ-quanta and the occurrence of γ-γ coincidences conclusively establish the decay scheme as suggested by Goldhaber and Hill, in which the β-transition is followed by the γ-rays in cascade. The energies and character of the γ-ray transitions are in close agreement with those predicted from the Bohr-Mottelson rotational model of the nucleus (Bohr and Mottelson 1953).