Molière radius
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: RM = 0.0265 X0 (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 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).[2]
Molière radii for typical materials used in calorimetry
- Caesium iodide: 3.5 cm[3]
- Liquid argon: 10.1 cm
- Liquid krypton: 4.7 cm[4]
- Lead tungstate crystals: 2.2 cm[5]
References
- ↑ Molière Radius
- ↑ Phillip R. Sloan, Brandon Fogel, "Creating a Physical Biology: The Three-Man Paper and Early Molecular Biology" University of Chicago Press, 2011
- ↑ http://pdg.lbl.gov/2014/AtomicNuclearProperties/HTML/cesium_iodide_CsI.html
- ↑ http://cds.cern.ch/record/256569/files/P00019924.pdf
- ↑ The CMS Collaboration (2006). "Chapter 1. Introduction". CMS Physics : Technical Design Report Volume 1: Detector Performance and Software. CERN. p. 14. ISBN 9789290832683.
CMS has chosen lead tungstate scintillating crystals for its ECAL. These crystals have short radiation (X0 = 0.89 cm) and Moliere (2.2 cm) lengths, are fast (80% of the light is emitted within 25 ns) and radiation hard (up to 10 Mrad).