Channeling and Coherent Bremsstrahlung Effects for Relativistic Positrons and Electrons

Channeling of positrons in silicon single crystals has been observed in transmission and scattering measurements for incident energies from 16 to 28 MeV. In addition, the forward bremsstrahlung intensity has been established as a new observable of the channeling phenomenon. Enhancement of the low-energy portion of the bremsstrahlung spectrum ($E_{\gamma }<1\mathrm{}$ MeV) has been observed with both positron and electron beams incident along the crystal axes; this enhancement is attributed to coherence effects in bremsstrahlung production.