Maximum is obviously 42 MT/kg. But how much of the energy is lost as neutrinos from pion and muon decay? Typical nucleon annihilation produces an average of 4,5 pions. Since the energy is 1880 MeV, each pion gets an average of 420 MeV, of which 140 MeV is rest mass. 1/3 of these are neutral pions which decay in a short distance to photons, which are captured by sea level air. How transparent are sea level air and common condensed substances to annihilation spectrum charged pions? Which proportion of these pions are captured by strong interaction with nuclei (resulting in fast nucleons, captured by air), and which proportion lives to decay to muons (where one half of the energy, and then 2/3 of the rest, is lost as neutrinos)?