There were several presentations at M&M which discussed the utility of "non-traditional" x-ray lines in EPMA, particularly as there is increasing interest in the use of low keV EPMA (<10 keV down to ~5-6-7 keV). In particular the Fe LL (Ll, not L one) line. Adjacent to it is the LN (Ln, not L eta) line which is sometimes indistinguishable from LL. Gopon et al (2013) showed the usefulness of the LL line for the transition element Fe where the La and Lb lines are problematic in the correct EPMA of Fe-silicides, using Fe metal for the Fe standard.
I have also done some experiments at low keV for some REE compounds and similarly found M gamma and M zeta to be useful, as the Ma-Mb lines can be extremely user-unfriendly lines (Fischer-Baun J. Applied Physics Vol 38, p 4830+). Namely, it can be difficult to distinguish exactly where the Ma and Mb are, when one may be bifurcated by the edge. And then even if it can be correctly determined, the analytical results are extremely wrong (eg. in a SmMgZn alloy, the Sm was ~24% too high using Ma)--much like the problem using Fe La in Fe-silicides.
In attempting to utilize all of these 'non-traditional' lines in _acquisition_ there have been many problems. One must "trick" the acquisition software because all (*one exception recently) do not support acquisition of these lines, so one must choose as the analytical line (to be peaked up and faked out) such as Mb. The problem arises when one wishes to see the _correct_ display of adjacent x-ray lines, as the software displays all positions (angstroms, sin theta, mm, keV) relative to the 'central element' which say is listed as Sm Mb when in fact it is Sm Mz.
Recently Cameca implemented the ability to acquire many non-traditional lines in their Peak Sight software, a nice first step, and there remains followup work to implement the correct matrix correction of the lines.
"It would be nice" to be able to directly acquire (vs 'faking out') the software some of these non-traditional lines in PfE. But I understand this is a difficult thing to implement. But a goal to be aimed for.