First observation of parametric X-rays produced by moderate relativistic protons and carbon nuclei in Si crystals

Spectral maxima of parametric X-ray radiation from moderately relativistic protons and carbon nuclei interacting with (0 0 1) silicon crystals have been observed for the first time. The PXR emitted due to the interaction of nuclei with silicon crystals in the Bragg geometry were detected by the semiconductor spectrometer. The positions of the radiation maxima in the spectra depend on the crystal angle and correspond to the theoretical values. The PXR yield per particle observed from carbon nuclei is considerably higher than from protons. This agrees with the theory statement about the Z2-dependence of the yield. The spectra contain the considerable contribution from side PXR reflections. The measurements have been performed at the Nuclotron (LHE JINR) extracted beams of 5 GeV protons and 2.2 GeV/u carbon nuclei. It was the first observation of PXR from heavy particles–relativistic nuclei. Moreover, the PXR was observed from particles with the lowest relativistic factor (γ = 3.36) among all used before.