${\mathrm{B}}^8$ has been observed as a 0.61±0.11 sec positron emitter produced by the following reactions: ${\mathrm{B}}^{10}(\gamma ,2n){\mathrm{B}}^8$, ${\mathrm{B}}^{11}(\gamma ,3n){\mathrm{B}}^8$, and ${\mathrm{C}}^{12}(\gamma ,p3n){\mathrm{B}}^8$. ${\mathrm{Li}}^9$ has been observed as a 0.19±0.05 sec beta minus emitter produced by the reaction, ${\mathrm{B}}^{11}(\gamma ,2p){\mathrm{Li}}^9$. Irradiation of elements from $Z=3\mathrm{}$ to $Z=9\mathrm{}$ with a 0-50 Mev gammaray spectrum failed to induce any other short-lived activities. In spite of this, ${\mathrm{B}}^{13}$, ${\mathrm{C}}^9$, and ${\mathrm{O}}^{13}$ are not ruled out as short-lived activities. ${\mathrm{Li}}^4$ is not produced in observable amounts through the reaction ${\mathrm{Li}}^6(\gamma ,2n){\mathrm{Li}}^4$ if it has a half-life between 0.1 sec and 1 min; it is probably particle unstable.

• Received 25 April 1952

DOI:https://doi.org/10.1103/PhysRev.87.557