A simple representation of spallation neutron energy spectra for ‘back of the envelope’ estimates

A simple approximate easy-to-use analytic formula is suggested for the absolute integrated-over-angle energy spectrum of neutrons from a high-Z spallation neutron target driven by 500–1500MeV proton beams. Overall, the formula is probably reliable to within a factor ~2–3, and could be useful for quickly making rough ‘back of the envelope’ estimates. •A simple formula for spallation neutron energy spectra for rough estimates.•Probably reliable to within a factor 2–3.•Useful for making back-of-the-envelope estimates of induced activities.