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Novel measurements of electromagnetic radiation above 10 MeV are presented for ultra intense laser pulse interactions with solids. A bright, highly directional source of γ rays was observed directly behind the target. The γ rays were produced by bremsstrahlung radiation from energetic electrons generated during the interaction. They were measured using the photoneutron reaction 63Cu(γ,n)62Cu in copper. The resulting activity was measured by coincidence counting the positron annihilation γ rays which were produced from the decay of Cu62. New measurements of the bremsstrahlung radiation at 1019 W cm−2 are also presented.
Norreys et al. (1999) studied this question.