A lower limit to the alpha half-life of ${\mathrm{Cm}}^{247}$ was previously reported as 4×${10}^7$ yr, but the determination reported here, with a curium sample containing 30 times more ${\mathrm{Cm}}^{247}$, yields a half-life of (1.64±0.24)×${10}^7$ yr. This result implies that no detectable amount of primordial ${\mathrm{Cm}}^{247}$ exists on earth and that ${\mathrm{Cm}}^{247}$ could not account for the high ${\mathrm{U}}^{235}$: ${\mathrm{U}}^{238}$ ratios reported for certain minerals.

• Received 25 February 1963

DOI:https://doi.org/10.1103/PhysRev.131.1249