Atomic and nuclear properties of materials:
Argon gas (Ar)

Quantity	Value	Units	Value	Units
Atomic number	18
Atomic mass	39.948(1)	g mole-1
Specific gravity (20° C, 1 atm)	1.66E-03	g cm-3
Mean excitation energy	188.0	eV
Minimum ionization	1.519	MeV g-1cm2	2.525E-03	MeV cm-1
Nuclear collision length	75.7	g cm-2	4.557E+04	cm
Nuclear interaction length	119.7	g cm-2	7.204E+04	cm
Pion collision length	101.3	g cm-2	6.097E+04	cm
Pion interaction length	149.0	g cm-2	8.964E+04	cm
Radiation length	19.55	g cm-2	1.176E+04	cm
Critical energy	38.03	MeV (for e-)	37.06	MeV (for e+)
Molière radius	10.90	g cm-2	6559.	cm
Plasma energy	0.79	eV
Muon critical energy	572.	GeV
Melting point	83.81	K	-189.3	C
Boiling point @ 1 atm	87.26	K	-185.9	C
Index of refraction (@ STP, Na D)	281.	(n-1)x106

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
Table of isotopes Warning: may not be current
x ray mass attenuation coefficients