With gaseous sources of ${\mathrm{As}}^{72}$ and ${\mathrm{As}}^{74}$, large nuclear resonance fluorescence effects have been observed for the 835-kev excited state of ${\mathrm{Ge}}^{72}$ and for the 596-kev excited state of ${\mathrm{Ge}}^{74}$. The angular distribution of the resonance radiation characterizes the spins of both these excited states as 2 and the spins of the ground states as 0.

From the magnitude of the resonance fluorescence effects, the mean lives of the 835-kev and 596-kev gamma-ray transitions were determined as (4.6±1.2)×${10}^{-12\mathrm{}}$ second and (1.9±0.3)×${10}^{-11\mathrm{}}$ second, respectively. These lifetimes are approximately one order of magnitude shorter than those expected for electric quadrupole transitions on the basis of the single particle model.

The influence of collisions in the gas on the observed resonance fluorescence effect was studied using the 596-kev level in ${\mathrm{Ge}}^{74}$.

• Received 14 September 1955

DOI:https://doi.org/10.1103/PhysRev.101.286