The double β decays of ${}^{100}\mathrm{Mo}$ and ${}^{150}\mathrm{Nd}$ were studied in a time projection chamber located 72 m underground. A 3275-h exposure of a 16.7-g sample of metallic Mo enriched to 97.4% in ${}^{100}\mathrm{Mo}$ resulted in a two-neutrino half-life, $T_{1/2}^{2\nu }{=(6.82\mathrm{}}_{-0.53}^{+0.38\mathrm{}}\pm 0.68)\times {10}^{18}\mathrm{y}.$ Similarly, a 6287-h exposure of 15.5 g of ${\mathrm{Nd}}_2{\mathrm{O}}_3$ enriched to 91% in ${}^{150}\mathrm{Nd}$ yielded $T_{1/2}^{2\nu }{=(6.75\mathrm{}}_{-0.42}^{+0.37\mathrm{}}\pm 0.68)\times {10}^{18}\mathrm{y}.$ Lower limits on half-lives for neutrinoless decay with and without majoron emission also have been measured.

• Received 12 June 1997

DOI:https://doi.org/10.1103/PhysRevC.56.2451