Atomic and nuclear properties of promethium (Pm)

Quantity	Value	Units	Value	Units
Atomic number	61
Atomic mass	[144.91275(3)]	g mole-1
Specific gravity	7.264	g cm-3
Mean excitation energy	560.0	eV
Minimum ionization	1.240	MeV g-1cm2	9.008	MeV cm-1
Nuclear collision length	103.5	g cm-2	14.25	cm
Nuclear interaction length	177.7	g cm-2	24.46	cm
Pion collision length	127.5	g cm-2	17.55	cm
Pion interaction length	204.9	g cm-2	28.20	cm
Radiation length	7.51	g cm-2	1.035	cm
Critical energy	9.83	MeV (for e-)	9.49	MeV (for e+)
Molière radius	16.21	g cm-2	2.231	cm
Plasma energy ℏωp	50.39	eV
Muon critical energy	180.	GeV

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 is no stable isotope, [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