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

We have reexamined the conditions for the enhancement of electron-positron pair photoproduction cross-section to occur due to the type-B coherent effe ct. Simple formulae to characterize the position and the bandwidth of the e nhancement for the hard collimated pairs are derived. We also examined the effect of interference among the atomic strings and found that, in some cas es it is almost identical to a random phase approximation while in other ca ses, phenomena analogous to the extinction law in X-ray diffraction may occ ur. (C) 2001 Elsevier Science B.V. All rights reserved.