The simultaneous direct mass measurements of 21 neutron-rich nuclei ranging from ${}_{}{}^{19}{}_{}{}^{}\mathrm{C}$ to ${}_{}{}^{37}{}_{}{}^{}\mathrm{P}$ have been performed with a new type of recoil spectrometer. The masses of ${}_{}{}^{19}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{27–28}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{32–34}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{36}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{37}{}_{}{}^{}\mathrm{P}$ have been determined for the first time. No evidence of an increase in the two-neutron separation energy as noted for ${}_{}{}^{31–32}{}_{}{}^{}\mathrm{Na}$ is observed for ${}_{}{}^{30–32}{}_{}{}^{}\mathrm{Mg}$ and ${}_{}{}^{32–34}{}_{}{}^{}\mathrm{Al}$.

• Received 18 August 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.3253