In- ̄ight annihilation during positron channeling
نویسندگان
چکیده
Energetic positrons propagating along low index directions in a crystal interact strongly with the periodic array of atoms via a process known as channeling. The trajectories of such channeled positrons can be manipulated to sample dierent spatial regions in the crystal. Here we report the ®rst observations of channeling eects on in̄ight annihilation radiation from positrons traversing a thin gold crystal. The channeling minimum yield for two-photon annihilation is shown to be signi®cantly enhanced compared to single photon annihilation due to the selective interaction of wellchanneled positrons with valence electrons in the interstitial regions of the crystal. Both classical and quantum calculation of annihilation yields are compared to the experimental data. Ó 2000 Elsevier Science B.V. All rights reserved.
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