Resonance-ionization mass spectrometry for high-resolution, mass-resolved spectra of rare isotopes

We show that resonance-ionization mass spectrometry is an excellent technique for acquiring high-resolution optical spectra of rare isotopes. To demonstrate the potential of this technique, hyperfine spectra of the D23/2∘←D23/2 lutetium transition at 22 125 cm−1 are presented for 176Lu, 175Lu, 174Lu, and 173Lu. The last-named two are rare isotopes with half-lives of 3.3 and 1.4 years, respectively, 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 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.