Production of intense, tunable, quasi -monochromatic X -rays using the RPI linear accelerator.

摘要

This research investigated the production of parametric X-rays (PXR) using the 60-MeV electron linear accelerator at Rensselaer Polytechnic Institute. PXR is an intense, energy tunable, and polarized X-ray source derived from the interaction of relativistic electrons and the periodic structure of crystal materials. In this work, PXR photon yields and the associated bremsstrahlung background were characterized for graphite, LiF, Si, Ge, Cu, and W target crystals. A model that considers the experimental geometry and crystal mosaicity was employed to predict PXR energy broadening. Measured energy linewidths consistently agreed with predicted values except in cases using poor quality graphite in which the mosaicity was greater than the PXR characteristic angle, 8.5 mrad for 60 MeV electrons. When the predicted energy linewidth was more narrow than our Si X-ray detector resolution, a near-absorption edge transmission technique was used to measure the PXR energy linewidth for Si(400) FWHM of 134 eV at 9.0 keV (2%) and Si(220) FWHM of 540 eV at 17.7 keV (3%).;An experimental study was conducted to select PXR target crystals most appropriate for X-ray production at typical mammography energies (17--20 keV). Low Z materials like graphite and LiF were most suitable for PXR production because of their low Bremsstrahlung production, electron scattering, and photon absorption. Graphite was most efficient at producing PXR photons while the LiF energy linewidth was narrower.;A theoretical model that considers electron multiple scattering, electron divergence, and crystal mosaicity was used to broaden the PXR photon distribution in order to calculate predicted PXR photon yield. This approach, proposed by A. P. Potylitsin, was allowed comparison of measured and predicted PXR yields. The relative error was typically below 0.5. In some cases with LiF, the differences between predicted and measured values were as low as 2% for LiF(400) and 13% for LiF(220). Finally, this work reports for the first time PXR imaging. This was achieved using LiF(220) interacting with 56 MeV electrons with electron beam currents up to 6 muA.