One can also use the molar attenuation coefficients ε ε i = N A ln ⁡ ⁡ 10 σ σ i , where N A is the Avogadro constant, to describe the attenuation coefficient in a way independent of the amount concentrations c i ( z ) = n i z N A of the attenuating species of the material sample: T = exp ⁡ ⁡ ( − − ∑ ∑ i = 1 N ln ⁡ ⁡ ( 10 ) N A ε ε i ∫ ∫ 0 ℓ ℓ n i ( z ) d z ) = exp ⁡ ⁡ ( − − ∑ ∑ i = 1 N ε ε i ∫ ∫ 0 ℓ ℓ n i ( z ) N A d z ) ln ⁡ ⁡ ( 10 ) = 10 ∧ ∧ ( − − ∑ ∑ i = 1 N ε ε i ∫ ∫ 0 ℓ ℓ c i ( z ) d z ) .