Various interfering factors, such as vibration and electrical interference, act to increase the FWHM of the output signal from the preamplifier FET from less than or equal to about 137 eV at 5.9 keV from 55 Fe at 1000 cps with a 40??S time constant to a greater value, e.g., greater than about 140 eV. The interfering factors convolve with the signal produced by an X-ray to increase the FWHM. See, G