Coulomb Excitation of States inTh232andU238

Abstract

The yield of gamma rays resulting from Coulomb excitation of states in ${\mathrm{Th}}^{232}$ and ${\mathrm{U}}^{238}$ with protons of 4- to 6-Mev energy have been measured. Gamma rays of 790-, 740-, and 613-kev energy from ${\mathrm{Th}}^{232}$ and of 1.02-Mev energy from ${\mathrm{U}}^{238}$ are observed. For ${\mathrm{Th}}^{232}$, the variation in gamma-ray yields with proton energy, the results from gamma-ray angular distributions, and the linear polarization measurements are consistent with the direct excitation of a 2+ state at 790-kev which decays by means of $E2\mathrm{}$ radiation to the $I=0+ \mathrm{and} 2+$ members of the ground-state rotational band. In view of the recent results from internal conversion electron measurements at Rice University, the 613-kev gamma ray is interpreted to be a transition from a $2+\beta$-vibrational state at 773 kev to the 4+ state at 163 kev. An interpretation of the observed gamma-ray yields is carried out taking a $\gamma$-vibrational state at 790 kev and a $\beta$-vibrational state at 773 kev. The $B{\mathrm{}\left(E2\mathrm{}\right)\mathrm{}}_d$ of the 2+ state at 50 kev in ${\mathrm{Th}}^{232}$ is about 150 times the single-particle estimate. The $B{\mathrm{}\left(E2\mathrm{}\right)\mathrm{}}_d$ of the vibrational states in ${\mathrm{Th}}^{232}$ and ${\mathrm{U}}^{238}$ are between 2 and 4 times the single-particle estimate. Combining Bernstein's relative internal conversion electron yields with our gamma-ray data, a value of (8±2)×${10}^{-2\mathrm{}}$ for the strength parameter $\rho$ is obtained for the $E0\mathrm{}$ transition between the 2+ state at 773 kev and the 2+ state at 50 kev in ${\mathrm{Th}}^{232}$.