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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. By definition, it is the radius of a cylinder containing on average 90% of the shower's energy deposition. It is related to the radiation length X0 by the following approximate relation: R = 0.0265 X0 (Z + 1.2), where Z is the atomic number. The Molière radius is useful in experimental particle physics in the design of calorimeters: a smaller Molière radius means better shower position resolution, and better shower separation due to a smaller degree shower overlaps.

The Molière radius is named after German physicist Paul Friederich Gaspard Gert Molière (1909–64).

Molière radii for typical materials used in calorimetry

  • Caesium iodide: 3.5 cm
  • Liquid argon: 10.1 cm
  • Liquid krypton: 4.7 cm
  • Lead tungstate crystals: 2.2 cm
  • References

    Molière radius Wikipedia

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