We report in this paper identification of the new isotope ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$. Uranium targets were irradiated with 28 GeV protons; after rapid retrieval of the target and separation of actinium from thorium, ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$ was allowed to decay into the known ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$ daughter. Exhaustive chemical purification was employed to permit the identification of ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$ via its characteristic $\gamma$ radiations. The half-life derived for ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$ from several experiments is 2.3±0.3 min. The production cross section for ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$ is 100 μb.

RADIOACTIVITY ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$ produced in ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$(p, 4p2n) reaction, measured $t_{\frac{1}{2}}$ through daughter nuclide ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$. Natural uranium target, 28 GeV protons, radiochemical separation, Ge(Li) $\gamma$ spectroscopy, genetic relationship. Production cross sections of several Th and Ac isotopes.

• Received 29 April 1983

DOI:https://doi.org/10.1103/PhysRevC.28.1379