An attempt was made to find the very neutron-rich isotope ${}_{}{}^{26}{}_{}{}^{}\mathrm{O}$ among the fragmentation products of a 90 MeV/nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ beam. This isotope has been predicted to be bound but was not observed in a previous experiment by Guillemaud-Mueller et al. As part of the search, the momentum distributions of all the oxygen isotopes in the range from ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ to ${}_{}{}^{24}{}_{}{}^{}\mathrm{O}$ were carefully determined so that the optimum separator setting for ${}_{}{}^{26}{}_{}{}^{}\mathrm{O}$ could be used. From an extrapolation of the counting rates of the lighter oxygen isotopes, we expected to observe several hundred events of ${}_{}{}^{26}{}_{}{}^{}\mathrm{O}$ during the measurement. However, no events could be attributed to ${}_{}{}^{26}{}_{}{}^{}\mathrm{O}$, thus indicating the particle instability of this isotope. The results for the production cross sections of 72 neutron-rich isotopes, ranging from ${}_{}{}^{38}{}_{}{}^{}\mathrm{P}$ to ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$, are presented and compared to predictions. © 1996 The American Physical Society.

• Received 27 July 1995

DOI:https://doi.org/10.1103/PhysRevC.53.647