The mass of ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ has been measured by counting delayed protons near the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}({}_{}{}^3{}_{}{}^{}\mathrm{He},n){}_{}{}^9{}_{}{}^{}\mathrm{C}$ threshold. The data are consistent with an $s$-wave threshold at $E_{3_{\mathrm{He}}}=8980\mathrm{}\pm 5$ keV, giving a ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ mass excess of 28 907±4 keV, and confirming the reported deviation of the $A=9\mathrm{}$, lowest $T=\frac{3}{2}$ quartet from the quadratic mass formula. The half-life of ${}_{}{}^9{}_{}{}^{}\mathrm{C}$, measured with a multiscaler, is 126.5 ± 2 msec.

• Received 9 October 1970

DOI:https://doi.org/10.1103/PhysRevC.3.438