0.1 keV 1.0 keV 10.0 keV 100 keV 1 MeV "Soft" "Hard" Soft gamma-rays Photon energy unit kev Convert photon energy to wavelength 1keV=1.6x109erg=hclλ，λ=12.4A the ionization potential of hydrogen:13.6 ev or 912A ·Temperature 1 keV~1.16 x 107K (hv =kT) Doppler shift a UV photon at 1240A to 1keV require a speed of 0.9998c 6/4/2022• Photon energy unit – keV • Convert photon energy to wavelength 1 keV = 1.6 x 10-9 erg = hc/λ, λ=12.4Å the ionization potential of hydrogen: 13.6 eV or 912Å • Temperature 1 keV ~ 1.16 x 107K (hν = kT) • Doppler shift a UV photon at 1240Å to 1keV require a speed of 0.9998c 6/4/2022