Development of an X-ray tube with two selective targets modulated by a magnetic field.

An energy-selective X-ray tube based on a magnetically controlled method is proposed here. An X-ray tube with two selective targets, modulated by a magnetic field, was developed for the X-ray fluorescence (XRF) analysis of multielement samples. The X-ray tube was small (20 cm length × 4 cm width) and had low power, being operated at 20 W (20 kV, 1 mA). It contained a thermionic cathode and two targets [copper (Cu) and chromium (Cr)] mounted on the anode. The electron beam was drifted by a modulated magnetic field to bombard either the Cu or Cr targets and so produce the required emission spectrum. Particle dynamics analysis software was used to simulate the particle tracking of the X-ray tube. The focal spot on the anode was successfully drifted, and a focal spot at 2 × 2.3 mm was obtained with a pinhole camera method. The XRF analysis of a standard sample (a mixture of FeO and CaCO) was measured by a silicon drift detector. When the bombarding target was changed from Cu to Cr, the characteristic calcium (Ca) X-rays that were detected were twice as strong as those of iron (Fe), but they had a similar excitation efficiency. It was demonstrated that this X-ray tube can provide fast exchangeable X-rays for XRF analysis by modulating the magnetic field intensity and can be further improved by optimizing the structure for alternative applications.