We have studied the alpha decay of ∼280-day ${\mathrm{Es}}^{254}$ to ${\mathrm{Bk}}^{250}$, and observed the following alpha groups: 6.486 MeV, 0.27%; 6.437, 93%; 6.424, 1.7%; 6.392, 0.13%; 6.367, 2.9%; 6.355, 0.74%; 6.331, 0.05%; 6.284, 0.16%; 6.276, 0.22%; 6.200, ∼0.05%; 6.193, ∼0.05%; 6.113, 0.33%; and 6.056, 0.16%. In addition, from conversion electron and gamma-ray (Ge and NaI) spectra, some 20 gamma-ray transitions were observed. Most of this information has been used in characterizing rather unambiguously four low-lying rotational bands in ${\mathrm{Bk}}^{250}$. The properties of these bands have been compared rather carefully with those predicted by considering the odd neutron and odd proton to move independently of each other. The predicted and observed properties are in surprisingly good agreement.

• Received 15 November 1965

DOI:https://doi.org/10.1103/PhysRev.144.1031