FEASIBILITY OF INTENSE MONOCHROMATIC X-RAY SOURCE IN THE 1-100 KEV RANGE BY PROTON BOMBARDMENT OF METALLIC TARGETS

摘要

X-ray sources produced by a standard x-ray tube coupled to a secondary anode and by proton irradiation generate x-ray spectra which are nearly equivalent and sufficiently monochromatic for many applications. The advantage with protons lies in the much higher intensity values achievable. A comprehensive theoretical and experimental study has been conducted on the production of intense sources of monochromatic x-rays by bombardment of pure element targets with protons and helium ions with energies between 10 and 100 MeV and very low currents (from nA to muA). The accompanying production of intense background due to nuclear reactions proved, however, to be unavoidable in practice, counterbalancing the advantage of the intense characteristic x-ray yield. By keeping the proton energy below the Coulomb barrier, no nuclear background is expected. A very intense source of monochromatic x-rays, tunable in the 1-100 keV range, can be obtained by coupling a low-energy (2-4 MeV), high-current proton accelerator with an irradiation chamber provided with a multiple target system and collimator. The radiofrequency quadrupole (RFQ) is a proton accelerator which is compact and reliable. Commerical versions can provide up to 1 mA average current at energies of 2-4 MeV. Estimates of the photon intensities achievable by 2 MeV/1 mA and 4 MeV/0.5 mA proton beams obtained from an RFQ indicate that such a compact source can provide fluxes larger than 10(13) s-1 sr-1 for x-ray energies up to about 6.4 keV (iron primary target), in excess of 10(11) s-1 sr-1 for x-ray energies up to about 26 keV (antimony primary target) and still around 10(10) s-1 sr-1 for the hardest x-ray energies produced by the heaviest targets. These figures are 4-6 orders of magnitude higher than those achievable with conventional systems. The power dissipation in the target (1-2 kW cm-2) can be handled with a conventional water cooling system. The energy can be tuned by selecting the appropriate target. Comparisons among intensities achievable from this compact photon source, conventional x-ray tubes and synchrotron light sources are presented. Fields where such a source can be applied are discussed. [References: 33]