Atomic and nuclear properties of materials:
Potassium (K )

Quantity	Value	Units	Value	Units
Atomic number	19
Atomic mass	39.0983(1)	g mole-1
Density	0.862	g cm-3
Minimum ionization	1.623	MeV g-1cm2	1.399	MeV cm-1
Nuclear collision length	75.4	g cm-2	87.44	cm
Nuclear interaction length	119.0	g cm-2	138.0	cm
Pion collision length	101.0	g cm-2	117.2	cm
Pion interaction length	148.1	g cm-2	171.8	cm
Radiation length	17.32	g cm-2	20.09	cm
Critical energy	31.62	MeV (for e-)	30.72	MeV (for e+)
Molière radius	11.61	g cm-2	13.47	cm
Plasma energy	18.65	eV
Muon critical energy	472.	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
Table of isotopes Warning: may not be current
x ray mass attenuation coefficients