Escape and fluorescence peaks

At X-ray energies greater than silicon K absorption edge, which we have measured for crystalline silicon to be 1839 eV, the response function of the device shows two distinct peaks in addition to the primary one. One of them at energy E_f = 1739 eV is due to the silicon fluorescent photons that have escaped far enough from the original site of interaction to be detected as a separate event. The other peak centered at energy E_e = E₀ - E_f, where E₀ is energy of the incident photon, is called an escape peak. It is formed by the electron clouds that are left when the flourescent photon carrying away energy E_f leaves silicon substrate or, again, is stopped far enough to be detected separately. The behavior of these peaks is reasonably well described by the model developed as a part of ACIS calibration program and is discussed in more detail in section 4.14. The relative amplitudes of these peaks as a function of energy, both experimentally measured and simulated, are shown in Fig. 4.128.