  Analytical formulae for the calculation of secondary particle yields in p-A
interactions are given. These formulae can be of great practical importance for
fast calculations of neutrino fluxes and for designing new neutrino beam-lines.
The formulae are based on a parameterization of the inclusive invariant cross
sections for secondary particle production measured in p-Be interactions. Data
collected in different energy ranges and kinematic regions are used. The
accuracy of the fit to the data with the empirical formulae adopted is within
the experimental uncertainties. Prescriptions to extrapolate this
parameterization to finite targets and to targets of different materials are
given. The results obtained are then used as an input for the simulation of
neutrino beams. We show that our approach describes well the main
characteristics of measured neutrino spectra at CERN. Thus it may be used in
fast simulations aiming at the optimisation of the proposed long-baseline
neutrino beams at CERN and FNAL. In particular we will show our predictions for
the CNGS beam from CERN to Gran Sasso.
