The quadrupole moment of the 8-μs fission isomer in ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ has been determined with a newly developed charge-plunger technique for measuring lifetimes of states decaying by converted transitions. With a statistical accuracy of 7%, values between 34 and 39 b are obtained, depending on the unknown isomeric spin. The deformation of the second minimum described by the axis ratio of a spheroid is deduced to be $\frac{c}{a}=2.0\mathrm{}\pm 0.1$.

• Received 26 October 1976

DOI:https://doi.org/10.1103/PhysRevLett.38.387