Calculations of the yield of neutrons due to the interaction of protons on a deuterium gas target have been carried out for the primary p - d breakup reaction as well as for the secondary processes due to nuclear reactions induced by the elastically scattered protons and deuterons. The experimental conditions of Bowman et al. reported in a recent work were simulated with respect to the measurements of neutron yields in the proton energy range 7 to 17 MeV. It is found that the primary breakup reaction is the main source of neutron production and the contribution to the neutron yield from the secondary processes is quite small, being of the order of 1% to 2%. Thus, the discrepancy reported by Bowman et al. between the measured neutron yields and the theoretical calculations based on the primary breakup reaction alone cannot be explained by the inclusion of secondary processes. The possible reasons for the observed discrepancy are discussed. The calculations were extended up to Ep = 100 MeV. The conclusion drawn by Bowman et al. regarding the energy cost per neutron at Ep = 100 MeV by extrapolating the empirical function fitted to the experimental data measured up to 17 MeV is not borne out by the present calculations.