Half-value thickness
The quantity half-value thickness (d½) is the amount of material that reduces the radiation intensity to half the original value. Instead of the linear half-value thickness d½ (in m), often the mass half-value thickness ρ×d½ (in kg·m-2) is given. Here, ρ is the density (in kg·m-3) of the material.The quantity attenuation coefficient (commonly denoted by the Greek letter μ) describes how easily electromagnetic radiation penetrates into matter. The relation between half-value thickness and attenuation coefficient is:
μ = ln(2) / d½