Nuclear resonance fluorescence techniques have been used to measure the mean lives of the first and second excited states of ${\mathrm{P}}^{31}$. The exciting $\gamma$ radiation was obtained by bombarding 99.999% pure phosphorous with 4.0- and 4.95-MeV protons. Self-absorption of the 1.26-MeV resonant radiation gives $\tau =\left({{7.16}_{-1.0\mathrm{}}}^{+1.3\mathrm{}}\right)\times {10}^{-13\mathrm{}}$ sec. Similarly, $\tau =\left({{4.2}_{-1.0\mathrm{}}}^{+1.5\mathrm{}}\right)\times {10}^{-13\mathrm{}}$ sec is found for the 2.23-MeV level. The angular distribution for resonant scattering of the 2.23-MeV radiation is consistent with the expected pure quadrupole nature of this $\frac{1}{2}-\frac{5}{2}-\frac{1}{2}$ transition. The angular distribution for resonant scattering by the 1.26-MeV level allows 4 values of the $\frac{E2\mathrm{}}{M1\mathrm{}}$ amplitude ratio, $\delta =-0.20\mathrm{}\pm 0.03, -1.12\mathrm{}\pm 0.08, 0.90\pm 0.06, \mathrm{and} 5\pm 0.8$. Only $\delta =-0.20\mathrm{}$ is consistent with the principal work of others on angular distributions and linear polarization. Our lifetime combined with Coulomb-excitation results gives $\left|\delta \right|=0.40\mathrm{}$, which is not compatible with our angular distribution.

• Received 28 June 1963

DOI:https://doi.org/10.1103/PhysRev.132.1205