When performing X-Ray microanalysis in the ESEM (Environmental Scanning Electron Microscope) or in the VP-SEM (Variable Pressure Scanning Electron Microscope), the operating conditions of the microscope must be optimized. This is to reduce the beam broadening of the incident electrons when they scatter with the gas molecules before entering into the specimen. As a result of this scattering, the incident beam is composed of two parts. The first part of the beam is the unscattered beam and the second part is the scattered beam, named the skirt. in high pressure and long working distances conditions, the diameter of the skirt may extend to several millimeters. in order to show the effect of the skirt on X-Ray generation, a copper strip was placed .5 mm away of the electron beam on a flat Al specimen. The peak to background ratio of the copper line was measured at different pressure (from 25 to 200 Pa) for Air as gas.