Time correlation of cosmic-ray-induced neutrons and gamma rays at sea level

The neutrons and gamma rays produced by cosmic ray interactions in spallation and evaporation processes of air nuclei are time-correlated. The occurrence of their counts in a fixed time interval is not a random (Poisson) distribution, but rather time-correlated bursts of counts. A computational model is developed to explore time correlations of cosmic-ray-induced background of neutrons and gammas at sea level. Their lifetimes in air showers, multiplicity distributions, coincidence count statistic, and excess variance are analyzed. The effects of latitude and area size on multiplicity and coincidence distributions are also studied. The coincidence count distributions and Feynman-Y statistic are used to reveal the duration of spallation processes and properties of multiplying media. It is found that the coincidence count distribution in fixed time intervals deviates from a Poisson distribution. The Feynman-Y is about an order of magnitude greater for gammas than that for neutrons. For both neutrons and gammas, the duration of time-correlated multiplying processes in air showers is ~250 µs.