γ decay from states at low excitation energy in the neutron-deficient isotope,Rn200, identified by correlated radioactive decay

The low-lying level structure of the neutron-deficient isotope ${}_{}{}^{200}{}_{}{}^{}\mathrm{Rn}$ has been studied using the ${}_{}{}^{176}{}_{}{}^{}\mathrm{Hf}$ ${(}^{28}$Si,4n) reaction at a beam energy of 142 MeV. Evaporation residues were selected using an in-flight recoil mass separator, the Argonne Fragment Mass Analyzer, and implanted in a double-sided silicon strip detector. Prompt γ rays in ${}_{}{}^{200}{}_{}{}^{}\mathrm{Rn}$ were observed at the target position using the AYEBALL array of 19 Compton-suppressed germanium detectors, and were identified by the subsequent radioactive decay of associated recoiling ions in the strip detector. Isotopic assignments of the nuclei produced were made on the basis of the mass-to-charge ratio of the recoiling ion and the energy and half-life of its α decay. Previous results concerning transitions in ${}_{}{}^{202}{}_{}{}^{}\mathrm{Rn}$ were confirmed. The level scheme deduced for ${}_{}{}^{200}{}_{}{}^{}\mathrm{Rn}$, compared with those of heavier radon isotopes, is not consistent with the onset of deformation predicted by theoretical calculations. The estimated production cross section for ${}_{}{}^{200}{}_{}{}^{}\mathrm{Rn}$ in this reaction was 5 μb. © 1996 The American Physical Society.