Preliminary results of the search for exotic nuclei in the $^{18}O+ ^{18}O$ reaction mass of $^{19}$N

A system has been built to identify low-cross section products of nuclear reactions and to accurately measure their energy. It includes a magnetic spectrometer and a detecting system in its focal plane consisting of two resistive-wire proportional counters and a set of four position-sensitive 5 cm-wide detectors. Six parameters are simultaneously determined: three positions, two Delta E-values, and the residual energy. This over-determination of the nature and energy of the detected nucleus is used to discriminate against background effects. In an experiment with a 91 MeV /sup 18/O beam from the Orsay MP-Tandem, /sup 19/N nuclei from the /sup 18/O(/sup 18/O,/sup 19/N) /sup 17/F reaction were observed and the mass excess of /sup 19/N was measured as 15.81+or-0.10 MeV.