The nuclear radiations associated with the $\alpha$ decay of ${\mathrm{Fm}}^{257}$ have been investigated by a variety of spectroscopic techniques. Alpha groups were observed with energies and intensities of ∼6.75, (0.4±0.2)%?; 6.696±0.003, (3.2±0.3)%; 6.519±0.002, (94±1)%; 6.441±0.003, (2.0±0.4)%; and ∼6.35 MeV, (∼0.5)%?. Gamma-ray transitions were seen in coincidence with $\alpha$ particles with energies of 242, 180, and 62 keV. The ground state of ${\mathrm{Fm}}^{257}$ is given the Nilsson assignment $\frac{9}{2}+\frac{9}{2}\left[615\mathrm{}\downarrow \right]$ as is the 242-keV state of ${\mathrm{Cf}}^{253}$. The ground state of ${\mathrm{Cf}}^{253}$ is given the assignment $\frac{7}{2}+\frac{7}{2}\left[613\mathrm{}\uparrow \right]$. For these bands in the daughter nucleus the rotational constants $\frac{{\hslash }^2}{2\mathfrak{J}}$ have the respective values of 7.1±0.4 and 7.0±0.1 keV, the largest values found yet in the very heavy elements. Some of the $\alpha$- and $\gamma$-ray transitions are interpreted in terms of a Coriolis interaction between the two assigned Nilsson levels in the daughter nucleus.

• Received 30 January 1967

DOI:https://doi.org/10.1103/PhysRev.158.1073