Description: Planar targets illuminated by the Petawatt laser system emit directed beams of photons with energies of MeVs. The laser pulses have durations of 0.5 or 5 psec, on target energies in excess of 100 joules, and focal-spot sizes that vary from 10 to 100 µm, producing peak intensities greater than 10<sup>19</sup> watts/cm<sup>;2</sup>. Arrays of PIN diodes, dosimeters and nuclear-activation detectors measure the angular distributions of photons with energies greater than 0.5 MeV. The PIN diodes, with 1 cm<sup>2</sup> by 500-µm sensitive volume, are housed in lead pigs with 2.5-cm thick walls. Measured emission intensities have been as high as 5x10<sup>13</sup> (gamma) MeV/steradian. The angular distributions are highly directed in forward directions, with significant variations on a shot-to-shot basis. Backward radiated intensities tend to be more than a decade lower than in forward direct
Date: November 10, 1998
Creator: Phillips, T.; Brown, C. G.; Cowan, T.; Hatchett, S.; Hunt, A.; Key, M. et al.
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