^Keller, O. L., Jr. Characterization of protactinium species in crystals and solutions by Raman and infrared spectroscopy. United States Atomic Energy Commission [Unclassified and Declassified Reports Published by the Atomic Energy Commission and Its Contractors], 1963. TID-7675. pp 72-85. ISSN: 0099-8524. CODEN: XAERAK.