Structure of iridium lines

The isotopic constitution of iridium was for the first time determined by Venkatesachar and Sibaiya from a study of the hyperfine structure of its arc line λ3513.67 A. It was shown that iridium consists of two odd isotopes of mass numbers 191 and 193, the isotope 193 being twice as abundant as the isotope 191. This result was afterwards corroborated by Dempster's mass-spectrograph analysis. With the view of determining the ratio of the nuclear magnetic moments of the two isotopes, the hyperfine structure, arising from the nuclear spin moments of (12)(h2�) and (32)(h2�) of the isotopes 191 and 193, respectively, has been investigated for a few more iridium lines using an aluminized Fabry-Perot etalon. From the results obtained for the hyperfine level separations of the isotopes, it is concluded that the ratio of the nuclear magnetic moments of Ir (191) and (193) is -0.92. © 1939 The American Physical Society