Four new isotopes of iridium have been prepared by bombarding isotope-enriched rhenium as well as natural rhenium with alpha-particles, and osmium with deuterons. Three of them have been identified as follows:

The 3.2-hr. period is an isomer of the 12.6-day ${\mathrm{Ir}}^{190}$.

Another weak activity, possibly ${\mathrm{Ir}}^{189}$, of more than 100-day half-life has been observed.

Four daughter activities of iridium (9.5-min., 6-hr., 35-hr. and $\mathrm{ca}$. 50-day radio osmium) have been found, and their possible genetic relations discussed.

A rhenium activity of $\mathrm{ca}$. 1-hr. half-life has been noticed in the Os+19-Mev deuteron experiment.

• Received 24 April 1950

DOI:https://doi.org/10.1103/PhysRev.79.582