 Synchrotron Radiation in the Geant4 Physics Reference Manual by Geant4 Collaboration

Physics Reference Manual: Synchrotron radiation. The critical mode number is $3{\gamma }^3/2$; the critical-energy formula gives ${\omega }_c=3{\gamma }^{3}c/(2\rho )$ for a circular orbit in a perpendicular field. A development-manual web page, not an exam answer source.