Three New Delayed Alpha-Emitters of Low Mass

Two new positron active isotopes, ${\mathrm{B}}^8$ and ${\mathrm{Na}}^{20}$, have been found to decay to excited states of ${\mathrm{Be}}^8$ and ${\mathrm{Ne}}^{20}$, which in turn decay "instantaneously" by alpha-emission. Their half-lives are 0.65±0.1 sec. and ¼ sec., respectively. ${\mathrm{N}}^{12}$ is also found to have a low energy positron group which leads to an $\alpha$-unstable excited state in ${\mathrm{C}}^{12}$. The masses of ${\mathrm{B}}^8$ and ${\mathrm{Na}}^{20}$ are 8.027 and 20.015, respectively. ${\mathrm{B}}^8$ decays by a 13.7±0.3-Mev positron, through the same excited state of ${\mathrm{Be}}^8$ as does ${\mathrm{Li}}^8$. Estimates of the energies of the excited state in ${\mathrm{C}}^{12}$ and ${\mathrm{Ne}}^{20}$ are made.