Sub-luminal pulses from cosmic ray air showers

Some of the signals produced by air showers in scintillators possess a distinctive feature, a sub-luminal pulse (SLP) following the normal one with a time delay of approximately 1.5 r/c. The average amplitude of the SLP corresponds to an energy deposit of about 50 MeV, three times as much as is deposited in a typical scintillator by vertical minimum ionizing muons. The SLP account for approximately 5% of the energy deposited in the atmosphere by IR showers with energy 10 to the 10th power GeV at impact parameters 1 km. Assuming that these pulses are due to neutrons travelling with a speed slightly less than c, they provide a unique means of estimating E sub h, the energy deposited by slow hadrons, in showers of this very high energy. On the other hand, if not allowed for properly, these pulses are liable to cause errors in estimating the impact parameters of large showers from pulse width observations.