Neutron spectra following negative muon capture on lead (left) and calcium (right). Dots are experimental data from references [29–32], histograms are FLUKA calculations. For the case of lead, the three curves correspond to a percentage of 2-body absorption of 0, 20 and 100% respectively. For the case of calcium, the curve corresponds to a 20% 2-body percentage which is the value adopted in the code on a phenomenological basis.