The emission of characteristic X-rays from any chemical element induced by beta particles of high energy (10 5 -10 6 eV) is much higher than photon excitation, with the possible exception of selective excitation. This work describes the properties of a variable energy X-ray generator that uses 9 0 Sr as a source of beta particles and a multitarget array in a transparent source geometry. This compact device provides, through suitable selection of the target material, over 30 monoenergetic lines spread uniformly in the energy range of between 6 and 100 keV. The X-ray photon flux thus generated has an intensity of between 10 2 -10 3 s - 1 sr - 1 per MBq of the beta source activity. With this single beta source, the X-ray yield is higher as compared with generators using 2 4 1 Am or other X- or gamma-ray sources with the same activity, and the line's intensity changes by less than a factor of three over the whole energy range.