Observation of narrow-band γ radiation from a boron-doped diamond superlattice with an 855 MeV electron beam

We report the first observation of narrow band 1.3 MeV $\gamma$ radiation from a crystalline diamond micro-undulator. A diamond superlattice was grown with a periodical varying boron doping profile. Four sinusoidally deformed (110) periods resulted with a period length of 5.0 $\mu$m and an amplitude of 0.098 nm. A channeling experiment was performed with the 855 MeV electron beam of the Mainz Microtron MAMI accelerator facility. A clear peak was detected with a large sodium iodide scintillation detector close to the expected photon energy of 1.28 MeV. Key characteristics of the peak, including photon energy, width and intensity, were reproduced fairly well by Monte-Carlo simulation calculations. Based on the latter, optimized boron doping profiles were designed for a hypothetical 3 GeV electron beam, enabling preparation of a highly directional $\gamma$-ray beam with a photon energy of 14.5 MeV. The predicted spectral bandwidth is 13\%, however, with a high energy continuum tail. The on-target photon flux at a beam current of 100 $\mu$A would be about $10^{12}$/s.