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Promethium (Z = 61) is an exclusively radioactive element with short half-lives of up to 17 years. Consequently, Pm sample amounts that can be safely handled in off-line laboratories are small and data on atomic transitions is scarce.
In order to access Pm for RIB facilities, extensive laser ionization scheme development was carried out at JGU Mainz. More than 1000 new optical transitions were recorded in the spectral ranges from 415 - 470 nm and 800 - 910 nm using pulsed Ti:sapphire lasers. From the obtained spectra several two- and three-step ionization schemes were identified. In this course the ionization potential of Pm could be experimentally determined for the first time via field ionization of weakly bound states. The precision of the ionization potential could be improved by three orders of magnitude [1].
For high-resolution spectroscopy of Pm isotopes first tests on $^{147}$Pm were carried out within the PI-LIST ion source unit, a RF quadrupole structure separating the hot atomizer region from a cold laser interaction region. Like this surface ions can be suppressed while the species of interest is resonantly ionized in crossed laser beam geometry, significantly reducing spectral Doppler broadening. Hyperfine spectra for two subsequent transitions in a newly developed RIS scheme were measured with linewidths of $\approx$ 120 MHz. Off-line spectroscopy of the isotopes $^{143,144,145,146}$Pm at JGU Mainz is envisaged for 2018.
[1] K. Wendt et al. Hyperfine Interact. 227, 55 (2014)
