Transition wavelengths and unresolved transition array statistics of ions with Z = 72 − 89

Potential extreme ultraviolet and soft x-ray radiation sources have been identified, using the flexible atomic code (FAC), as emission peaks arising from the 4d–4f and 4p–4d transitions in Pd-like to Rb-like ions of hafnium through actinium. The effects of configuration interaction are investigated and for increasing nuclear charge, these strong emitters are seen to separate and move to shorter wavelengths. Each source is characterized using the unresolved transition array model. They are proposed to complement the currently used nitrogen and argon sources in the 'water window', and as possible successors to tin in next-generation lithography.