Isotopes of emanation (element 86) with 126 or fewer neutrons were prepared at the Heavy Ion Linear Accelerator by bombardment of platinum, gold, mercury, and thallium targets with ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ nuclei. Several techniques were developed for isolation of the gaseous products. Si(Au) surface-barrier detectors were used to measure $\alpha$ particles emitted by emanation isotopes and by their polonium and astatine daughters. Mass- number assignments of new isotopes of mass 201 through 205 were based on genetic relationships and on excitation functions. The probable nature of the isomerism observed in ${}_{}{}^{203}{}_{}{}^{}\mathrm{Em}$ is discussed. Properties of isotopes with masses 206 through 212 were confirmed.

• Received 19 January 1967

DOI:https://doi.org/10.1103/PhysRev.159.1013