Columbia subject headings:
Actinide elements--Congresses.
Rare earth metals--Congresses.
Spectrum analysis--Congresses.
Harvard subject headings:
Actinide elements--Congresses.
Rare earth metals--Congresses
Spectrum analysis--Congresses
Princeton subject headings:
Actinide elements--Congresses.
Rare earth metals--Congresses.
Spectrum analysis--Congresses.