Theoretical studies on level structures and transition properties of neptunium ions W.D. Zhou, C.Z. Dong, Q.M. Wang, X.L. Wang and I.A. Saber Eur. Phys. J. D, 66 10 (2012) 260 Published online: 11 October 2012 DOI: 10.1140/epjd/e2012-30321-0