The nuclear $\gamma$ resonances for ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ in the compound (U${\mathrm{O}}_2$)Rb${\left(\mathrm{N}{\mathrm{O}}_3\right)}_3$ have been observed using sources of Pu${\mathrm{O}}_2$ and Pu${\mathrm{Al}}_4$. Nuclear deformations of the U isotopes are observed to change through the ratios of the electric quadrupole moments. Using previous $B\left(E2\mathrm{}\right)\mathrm{}$ measurements the electric field gradient at the uranium site has been calculated for this compound from our data. The isomer shift of ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ has been measured for (U${\mathrm{O}}_2$)Rb${\left(\mathrm{N}{\mathrm{O}}_3\right)}_3$ and for the two sources Pu${\mathrm{O}}_2$ and Pu${\mathrm{Al}}_4$. Calculations of electronic charge density changes at uranium nuclei between source and absorbers give a fractional decrease in the rms nuclear radius in the transition from the ground to the excited state of ${\left(\frac{\delta 〈r_n^2〉}{〈r_n^2〉} \right)}_{{}_{}{}^{234}{}_{}{}^{}\mathrm{U}}=(-12.2\mathrm{}\pm 5.9)\times {10}^{-6\mathrm{}}$.

• Received 16 June 1972

DOI:https://doi.org/10.1103/PhysRevB.9.2838