It has been proposed that a nucleus may be excited by first exciting the atom’s electrons with UV photons. The incident photons couple to the electrons, which would then couple via a virtual photon to the nucleus. As a test case, experiments with ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ have been performed. A pulsed infrared laser produces an atomic vapor of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ which is then bombarded by a high-brightness UV laser beam. The resulting ions are collected. The first excited nuclear state of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ has a 26-min half-life and decays by internal conversion, resulting in emission of an atomic electron. These conversion electrons are detected by a channel electron multiplier. An upper limit of 4.0×${10}^{\mathrm{-}5}$ has been obtained for the probability of exciting the nucleus of a ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ atom that is in the 248-nm UV beam for 700 fs at an irradiance in the range of 1.0×${10}^{15}$ to 2.5×${10}^{15}$ W/${\mathrm{cm}}^2$.

• Received 22 May 1992

DOI:https://doi.org/10.1103/PhysRevC.46.852