^ abcdefg
Haire, Richard G. (2006). “Neptunium”. In Morss; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer Science+Business Media. pp. 730–736. doi:10.1007/1-4020-3598-5_9. ISBN1-4020-3555-1
^Zachariasen, W. H. (1949). “Crystal chemical studies of the 5f-series of elements. XII. New compounds representing known structure types”. Acta Crystallographica2 (6): 388–390. doi:10.1107/S0365110X49001016.