Activity median aerodynamic diameter

In the context of radiation protection, activity median aerodynamic diameter (AMAD) is one of two parameters influencing the deposition of inhaled particles, the other being the geometric standard deviation of the particle size distribution. The AMAD is the value of aerodynamic diameter for which 50% of the airborne activity in a given aerosol is associated with particles smaller than the AMAD, and 50% of the activity is associated with particles larger than the AMAD. The AMAD is used in internal dosimetry as a means of simplifying the true distribution of aerodynamic diameters of a given aerosol as a single value. It is used to describe those particle sizes for which deposition depends chiefly on inertial impaction and sedimentation.