New search for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>26</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>

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. \textcopyright{} 1996 The American Physical Society.

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