Molière radius

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The Molière radius is a characteristic constant of a material giving the scale of the transverse dimension of the fully contained electromagnetic showers initiated by an incident high energy electron or photon. It is related to the radiation length $X 0$ by the following approximate relation:

$\,\! R_M=0.0265X_0(Z+1.2),$

where $Z$ is the atomic number^[1]. The Molière radius is useful in experimental particle physics in the design of calorimeters: a smaller Molière radius means a smaller degree shower overlaps, and consequently a better shower separation.