Derivation of the critical angle for Mach reflection for strong shock waves

In the process of shock-wave reflection at a surface, a transition from regular to Mach reflection occurs when the angle of incidence exceeds a certain critical value. This critical angle, which depends on the Mach number of the propagating shock wave and gamma, the adiabatic exponent of the medium, is well approximated in many experimental situations by its value in the limit of infinite Mach number. Unfortunately, the often-cited critical angle for infinitely strong shock waves is incorrect. We present a short analysis of the process of shock-wave reflection and discuss the condition for infinitely strong shock waves. The exact and approximate solutions for the dependence of the critical angle on the adiabatic exponent of the medium are also compared with the above-mentioned formula.