ɐnˈʌðɚ pətˈɛnʃəl pɹˈɑːbləm ɪz ðæt fˈɪləmənt dᵻɡɹɐdˈeɪʃən ɪnðɪ ᵻlˈɛktɹɑːn ɡˈʌn ɹɪzˈʌlts ɪn ɐ nˈɑːnjˈuːnɪfˌɔːɹm ɪvˌæpɚɹˈeɪʃən ɹˈeɪt.
Another potential problem is that filament degradation in the electron gun results in a non-uniform evaporation rate.