The "Level Width" is the uncertainty in the energy of a quantum-mechanical system having discrete energy levels in a state that is not strictly stationary. The system may be an atom, a molecule, or an atomic nucleus.
Applicable units are those of quantitykind:LevelWidth
http://encyclopedia2.thefreedictionary.com/Level+Width
The "Level Width" is the uncertainty in the energy of a quantum-mechanical system having discrete energy levels in a state that is not strictly stationary. The system may be an atom, a molecule, or an atomic nucleus.
$\Gamma = \frac{\hbar}{\tau}$, where $\hbar$ is the reduced Planck constant and $\tau$ is the mean lifetime.
http://www.iso.org/iso/catalogue_detail?csnumber=31895