# Linear Attenuation Coefficient Motivation: [[Mean Free Path]] relevant concept The linear attenuation coefficient ($\mu$) is the sum of the cross-sections of the three types of gamma interactions with matter. Since the cross-sections are probabilities, we can sum them to get to total linear attenuation coefficient. $\mu = \tau + \sigma + \kappa $ where: - $\tau$ is the [[Photoelectric Effect]] cross-section - $\sigma$ is the [[Compton Scattering]] cross-section - $\kappa$ is the [[Pair Production]] cross-section The linear attenuation coefficient can become the mass attenuation coefficient by dividing the linear attenuation coefficient by the density of the medium ($\rho$). See also: [[Mass Energy-Absorption Coefficient]]