Density effect for the X-ray synchrotron radiation in a medium

The dependences of the energy loss and the number of photons of the X-ray synchrotron radiation produced by ultrarelativistic electrons moving in a magnetic field in a medium on the Lorentz factor are discussed. Calculations show the presence of the cut-off Lorentz factor depending, for a given magnetic field, on the electron density of a medium, below which a medium strongly suppresses the radiation yield. Above the cut-off Lorentz factor, both the energy loss and the number of photons of the X-ray synchrotron radiation experience an enhanced relativistic rise as compared with vacuum.