Atomic and nuclear properties of francium (Fr)
QuantityValueUnits ValueUnits
Atomic number 87     
Atomic mass [223.01974(2)] g mol-1   
Density 1.870 g cm-3   
Mean excitation energy 827.0 eV   
Minimum ionization 1.118 MeV g-1cm2 2.091 MeV cm-1
Nuclear interaction length 204.6 g cm-2 109.4 cm
Nuclear collision length 116.4 g cm-2 62.27 cm
Pion interaction length 230.6 g cm-2 123.3 cm
Pion collision length 139.5 g cm-2 74.62 cm
Radiation length 6.19 g cm-2 3.309 cm
Critical energy 7.59 MeV (for e-) 7.32 MeV (for e+)
Muon critical energy 143. GeV   
Molière radius 17.29 g cm-2 9.247 cm
Plasma energy ωp 24.61 eV   
Melting point 300.1 K 27.00 C
Boiling point @ 1 atm 950.2 K 677.0 C
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: Francium is less stable than any other element lighter than nobelium, element 102.
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
x ray mass attenuation coefficients from NIST