Energy levels of ²⁴⁷Cm populated in the α decay of ₉₈²⁵¹Cf

α-Particle, conversion-electron, and γ-ray singles spectra of ²⁵¹Cf sources containing few Bq activities were measured with high-resolution semiconductor detectors. α-γ coincidence and level half-life measurements were also performed. On the basis of these measurements the following single-particle states have been identified in ²⁴⁷Cm: 9∕2⁻[734], 0 keV; 5∕2⁺[622], 227.4 keV; 7∕2⁺[624], 285.4 keV; 1∕2⁺[620], 404.9 keV; 1∕2⁺[631], 518.6 keV. The measured single-particle energies are in good agreement with energies calculated with a Woods-Saxon single-particle potential. From the measured half-life of the 227.4-keV level and the E3 branching ratio, a B(E3) value of 5 W.u. has been deduced between the 5∕2⁺[622] and 9∕2⁻[734] bands. The large B(E3) value is an indication of octupole mixing in the 227.4-keV level.