Yu.P. Kunashenko

Enhanced type-B coherent effect in collimated electron-positron photoproduction from Si crystal

Abstract The relative cross section of pair creation from a silicon single crystal has been measured with a bremsstrahlung beam from 350 MeV electrons. A clear enhancement was observed above 230 MeV as expected from the theory based on the type-B coherent effect.

Energy spectrum of low energy positrons generated by radiation from relativistic electrons channeled in a crystal

Abstract The shape of positron energy spectra with the energy up to 50 MeV, generated by conversion of planar channeling radiation from relativistic electrons into electron–positron pairs in a thin amorphous converter has been studied by means of numerical calculations. The results obtained show that the shape of the positron energy spectrum depends on several parameters: on the initial electron energy, on the alignment of the crystal with respect to the electron beam, on the type of the crystal where the initial electrons are channeled, and on the crystal temperature.

On the possible experiments on coherent production of relativistic positronium in a crystal

Abstract Generation of relativistic singlet positronium (Ps) atoms by high-energy photons and electrons in amorphous and aligned crystal targets, as well as their break-up due to interaction with target atoms, is considered. The detailed numerical calculations show that due to coherence effect in a crystal target, the significant enhancement of positronium yield, at certain positronium energies and emission angles, can be achieved. The possible experiments with tagged photon beam, with bremsstrahlung (BS) photon beam and electron beam are proposed for planned REFER facility at Hiroshima University.

Coherent creation of electron-positron pairs in bound state by high energy photons and charged particles in a crystal

Abstract New brilliant coherent effects arise for e + e − pair creation by high energy photons in a crystal, when e + and e − form the neutral bound state (positronium atom moving with relativistic velocity), and for e + e − pair creation by relativistic heavy particles passing through the crystal, when e − (e + ) is captured into the K-shell of the projectile particles.

Radiation of relativistic nuclei transmitting through condensed matter

Abstract The possibilities of application of a relativistic nuclei accelerator in generating different types radiation during relativistic nuclei transmission through matter are discussed. It is shown that the radiation of relativistic nuclei can be used as a new monochromatic photon source in keV and MeV regions.

Experimental and theoretical features of hard-collimated type-B coherent high energy pair production

Abstract We have reexamined the conditions for the enhancement of electron–positron pair photoproduction cross-section to occur due to the type-B coherent effect. Simple formulae to characterize the position and the bandwidth of the enhancement for the hard collimated pairs are derived. We also examined the effect of interference among the atomic strings and found that, in some cases it is almost identical to a random phase approximation while in other cases, phenomena analogous to the extinction law in X-ray diffraction may occur.

From “narrow pairs” to relativistic positronium atom: evolution of coherent peaks for type-B photoproduction of electron-positron pairs in a crystal

Abstract It is shown, that the brilliance of coherent peak for type-B photoproduction in a crystal increases significantly for the pairs emitted with close momenta and is maximal for the case of coherent photoproduction of bound e+e− pair — the relativistic positronium atom.

Coherent Production of Relativistic Singlet Ps Atoms by High Energy Photons and Electrons in Aligned Crystals - Revisited

Cross-sections of coherent production of relativistic (moving with relativistic velocities) singlet Ps atoms in the ultrathin crystal have been calculated and estimations of counting rates are obtained to propose the experiments.

Parametric x-ray radiation generated by 5.7-MeV electrons in a pyrolytic-graphite crystal

Parametric x-ray radiation is observed in a mosaic pyrolytic-graphite crystal irradiated with a 5.7-MeV electron beam. The first-order (002) reflection of parametric x-ray radiation is detected in Bragg geometry. In the measured spectra, there is a peak at about 8 keV. The detector used is arranged at an angle of ΘD=2ΘB=27° with respect to the electron beam, where ΘB is the Bragg angle. The target thickness is 0.3 mm. The spectra of parametric x-ray radiation are measured at various angles of target orientation with respect to the axis of the incident-electron beam.

Coherent Type-B e+e- Pair Production by Photons in a Crystal

An overview of theoretical and experimental studies of the coherent type-B e+e-pair production by photons in aligned crystals performed at Nuclear Physics Institute at Tomsk Polytechnic University is given.