Influence of Beam Divergence and Crystal Mosaic Structure upon Parametric X-ray Radiation Characteristics

Based on kinematic model of parametric X-ray radiation (PXR), an approach for calculation of PXR characteristics (spectrum, intensity, polarization and yield) has been developed. The approach allows to take into account the beam divergence, mosaicity, aperture sizes, influence of K-edge, etc. using a uniform technique. 1. The existing theoretical models [1-3] describe the process of parametricX-ray radiation (PXR) for the monodirected charged particles beam interacting with sufficiently thin ideal crystals whose multiple scattering can be neglected. The real conditions of an experiment, however, are far from being ideal. To provide a quantitative comparison of the theoretical and experimental data we have to correctly take into account such phenomena as beam divergence, mosaicity, detector’s finite aperture, effects of the K-edge absorption and some other factors. The authors of [4] developed a phenomenological approach making it possible to approximately account for the effects of multiple scattering of particles in the target upon photon angular distribution and PXR spectrum. They assumed that multiple scattering leads to effective broadening of angular distribution of virtual photons connected with incidence particle. This approach made it possible to describe the experimental results obtained for thin perfect crystals. However, in the experiments [5-7] there was noted a significant discrepancy between the data by the proposed model and those of the experiment. The authors of [5] observed that angular distribution of PXR became narrower with decreasing electron energy. Experimental results in [6,7] show that the widths of orientational dependences (OD) of PXR yield are essentially less than the calculated values for the thick crystal target used. The authors of work [6] proposed an approach where the processes of PXR emission and multiple scattering are independent (incoherent model). This approach gives results close to the experiment and may be used for corrected account of multiple scattering. In [8] it was shown theoretically that mosaicity of crystal target has no effect on the total PXR intensity. Recently in [9] studied experimentally were mosaic structure effects on the PXR yield and spectral characteristics. The results obtained for higher orders of PXR show disagreement with the model [4]. The authors of [10] developed a method for the account of mosaicity based on convolution of PXR angular distribution with effective distribution including multiple scattering and mosaicity in the same manner. The effect of these factors must be different. The present work offers an approach providing a uniform technique, within the kinematic model, to calculate the PXR characteristics (spectrum, polarization, angular spread, photon yield into a finite aperture for any experimental environment, photon yield into an open cone, brightness, i.e. the PXR intensity per a solid angle unit) taking