Abstract

Previous isotope ratio measurements using resonance ionization mass spectrometry (RIMS) have used element selective photoionization with isotope ratios measured by dispersion of ions in a mass spectrometer. To increase the accuracy and dynamic range of isotope ratio measurements, it may be necessary to use isotopically selective ionization. To be successful in this task it is necessary to know isotope shifts and hyperfine structures of the optical transition(s) used for the isotopes of interest. We are particularly interested in rare and sometimes highly radioactive elements for which this information is not readily available. We demonstrate that the sensitivity and mass selectivity of the RIMS technique itself can be used to obtain the needed spectra. With this goal in mind, RIMS was used to acquire high-resolution optical spectra of rare isotopes. To demonstrate the potential of this technique, hyperfine spectra of the ${}^2{D}_{3/2}^0{\leftarrow }^2{D}_{3/2}$ lutetium transition at 22,125 cm^–1 are presented for ¹⁷⁶Lu, ¹⁷⁵Lu, ¹⁷⁴Lu, and ¹⁷³Lu. The latter two are rare isotopes with half-lives of 3.3 and 1.4 yr whose optical spectroscopy has not previously been explored. Sensitivity is documented by the fact that the total amount of these rare isotopes in our sample was 2 × 10^–10 g and 3 × 10^–11 g. Analysis of the spectra confirms that the spin of ¹⁷⁴Lu is unity and yields values for the hyperfine constants and isotope shifts of these nuclei.

© 1985 Optical Society of America