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

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 near ly equivalent and sufficiently monochromatic for many applications. Th e advantage with protons lies in the much higher intensity values achi evable. A comprehensive theoretical and experimental study has been co nducted on the production of intense sources of monochromatic x-rays b y bombardment of pure element targets with protons and helium ions wit h energies between 10 and 100 MeV and very low currents (from nA to mu A). The accompanying production of intense background due to nuclear r eactions proved, however, to be unavoidable in practice, counterbalanc ing the advantage of the intense characteristic x-ray yield. By keepin g the proton energy below the Coulomb barrier, no nuclear background i s 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 provide d with a multiple target system and collimator. The radiofrequency qua drupole (RFQ) is a proton accelerator which is compact and reliable. C ommerical 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 su ch 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 o f 10(11) s-1 sr-1 for x-ray energies up to about 26 keV (antimony prim ary target) and still around 10(10) s-1 sr-1 for the hardest x-ray ene rgies produced by the heaviest targets. These figures are 4-6 orders o f magnitude higher than those achievable with conventional systems. Th e 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 selectin g the appropriate target. Comparisons among intensities achievable fro m this compact photon source, conventional x-ray tubes and synchrotron light sources are presented. Fields where such a source can be applie d are discussed.