A search has been made for the spontaneous emission of neutral pions from Pb, Bi, Th, U, and ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$. None has been observed and for the most likely candidate, ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$, the limit is 3.3×${10}^{-10\mathrm{}}$ of spontaneous fission with a 90% confidence level.

• Received 30 August 1988

DOI:https://doi.org/10.1103/PhysRevC.39.295