A comparatively fast, time-dependent code for the interpretation of neutron emission rates of neutral-beam-heated tokamak plasmas which is based on a Fokker-Planck model for injected ions is presented. The code includes a package for calculating line-integrated time dependent neutron spectra which can be readily compared with measured spectra. Time-dependent interpretation calculations of dilution ratios nD/ne, for several JET discharges which cover a wide range of plasma conditions are presented. The results for the inferred dilution ratios are shown to be in good agreement with the experimental data. By using the measured and calculated neutron spectra the deuteron temperature can be inferred. Combining the calculations for the deuteron temperatures and the dilution ratios, a consistent set of these plasma parameters can be obtained. Results from this method are confirmed by data of independent measurements.