Photoproduction of electron-positron pairs in the presence of   hyperacoustic oscillations
  We report on the recent progress in the investigation of the influence of hyperacoustic vibrations on the coherent electron-positron pair creation by high-energy photons in crystals. In dependence of the values for the parameters, the presence of the deformation field can either enhance or reduce the cross-section. This can be used to control the parameters of the positron sources for storage rings and colliders. 
A. R. Mkrtchyan, L. Sh. Grigoryan, A. A. Saharian, V. V. Parazian