Protactinium

Britannica Nobel Prize: Protactinium - Overview and basic data.
www.britannica.com/nobel/micro/483_52.html

ChemGlobe: Protactinium - Electronic, thermal, and steric data along with an isotope table.
partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/91.html

ChemicalElements.com: Protactinium - Basic information, atomic structure, and isotopes.
www.chemicalelements.com/elements/pa.html

EnvironmentalChemistry.com: Protactinium - Atomic structure, chemical and physical properties, and table of nuclides.
environmentalchemistry.com/yogi/periodic/Pa.html

It's Elemental: Protactinium - Basic physical and historical information.
education.jlab.org/itselemental/ele091.html

LANL: Protactinium - Basic information and history.
periodic.lanl.gov/elements/91.html

Visual Elements: Protactinium - General and physical information, source, and key isotopes.
www.chemsoc.org/viselements/pages/protactinium.html

Radiochemistry of Protactinium - Full text of the monograph by H. W. Kirby (Mound Laboratory, Miamisburg, Ohio). [PDF] <small>(December, 1959)</small>
lib-www.lanl.gov/cgi-bin/getfile?rc000046.pdf