93 - Neptunium

Buttons of neptunium metal.

Neptunium metal button.

Neptunium oxidation states +3 to +7.
Np (III) is violet (similar to promethium).
Np (IV) is yellowish green.
Np (V) is green-blue.
Np (VI) is rose.

Neptunium oxidation states.

Neptunium oxide.

A nickel plated sphere of neptunium, used in an experiment to determine the critical mass of this element.

References

http://www.lenntech.com/Periodic-chart-elements/Np-en.htm - Metal button image.
http://www-lab.imr.tohoku.ac.jp/~wshiolab/Metal_Prep/Metal_Prep.htm - Metal button process description and image..
http://www.lanl.gov/orgs/pa/newsbulletin/2002/10/21/text01.shtml - Criticality test.
http://www.imr-oarai.jp/en/research/research2-3.html - Oxidation state colors.

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