On the Feynman-alpha formula for fast neutrons
  In this contribution, a stochastic theory for a branching process in a neutron population with two energy levels is investigated. In particular, a variance to mean or Feynman-alpha formula is derived in this generalized scenario using the Kolmogorov forward or master equation theory for the probabilities in a system with a compound Poisson source. 
Johan Anderson, Lenard Pal and Imre Pazsit
physics.plasm-ph math-ph math.MP nucl-ex