  NEXT-DEMO is a 1:4.5 scale prototype of the NEXT100 detector, a high-pressure
xenon gas TPC that will search for the neutrinoless double beta decay of
$^{136}$Xe. X-ray energy depositions produced by the de-excitation of Xenon
atoms after the interaction of gamma rays from radioactive sources have been
used to characterize the response of the detector obtaining the spatial
calibration needed for close-to-optimal energy resolution. Our result, 5.5%
FWHM at 30 keV, extrapolates to 0.6% FWHM at the Q value of $^{136}$Xe.
Additionally, alpha decays from radon have been used to measure several
detection properties and parameters of xenon gas such as electron-ion
recombination, electron drift velocity, diffusion and primary scintillation
light yield. Alpha spectroscopy is also used to quantify the activity of radon
inside the detector, a potential source of background for most double beta
decay experiments.
