Atomic and nuclear properties of materials:
Actinium (Ac)

Quantity	Value	Units	Value	Units
Atomic number	89
Atomic mass	[227.0278]	g mole-1
Specific gravity	10.1	g cm-3
Minimum ionization	1.112	MeV g-1cm2	11.19	MeV cm-1
Nuclear collision length	117.0	g cm-2	11.62	cm
Nuclear interaction length	205.8	g cm-2	20.43	cm
Radiation length	6.06	g cm-2	0.6016	cm
Critical energy	7.00	MeV (for e-)	6.75	MeV (for e+)
Molière radius	18.34	g cm-2	1.821	cm
Plasma energy	57.25	eV
Muon critical energy	134.	GeV

For muons, dE/dx = a(E) + b(E) E. Tables of b(E): PS PDF TEXT
Table of muon dE/dx and Range: PS PDF TEXT
Explanation of some entries
Note: Since there is no stable isotope, given atomic mass is that of the longest-lived known isotope as of Jan 2007.
Table of isotopes
x ray mass attenuation coefficients