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First observation of ortho-positronium with the J-PET tomograph. (arXiv:2006.07467v1 [physics.ins-det]) http://arxiv.org/abs/2006.07467
First observation of ortho-positronium with the J-PET tomograph. (arXiv:2006.07467v1 [physics.ins-det]) http://arxiv.org/abs/2006.07467