Atomic and nuclear properties of neptunium (Np)
QuantityValueUnits ValueUnits
Atomic number 93     
Atomic mass [237.04817(2)] g mol-1   
Density 20.25 g cm-3   
Mean excitation energy 902.0 eV   
Minimum ionization 1.095 MeV g-1cm2 22.17 MeV cm-1
Nuclear interaction length 208.7 g cm-2 10.31 cm
Nuclear collision length 118.5 g cm-2 5.850 cm
Pion interaction length 234.7 g cm-2 11.59 cm
Pion collision length 141.4 g cm-2 6.984 cm
Radiation length 5.87 g cm-2 0.2897 cm
Critical energy 6.57 MeV (for e-) 6.33 MeV (for e+)
Muon critical energy 127. GeV   
Molière radius 18.93 g cm-2 0.9349 cm
Plasma energy ωp 81.22 eV   
For muons, dE/dx = a(E) + b(E) E. Tables of b(E): PDF TEXT
Table of muon dE/dx and Range: PDF TEXT
Explanation of some entries
Note: Since there are no stable isotopes, [atomic mass] is that of the longest-lived isotope known as of Jun 2017.
Table of isotopes via WIKIPEDIA