Fast neutron spectral yield from the interaction of 20 MeV protons with thick Be and C targets are measured using CR-39 detectors. An image analysing program (autoTRAK_n) dedicated for neutron spectrum generation and dose estimation is developed based on the analysis of greylevel variations within each track and is used in the present study. The most important parameters for neutron spectrometry, i.e., track depth (length) and angle of all neutron-induced recoil tracks are determined using autoTRAK_n. The methodology is tested successfully to reproduce the spectra of some standard neutron sources which was reported earlier. In this study, autoTRAK_n is applied to generate neutron spectra from the above mentioned reactions, i.e., ⁹Be(p, n), ¹²C(p, n) and the neutron yields (total number of neutrons per projectile) for both the reactions are determined by folding the track density with the detector response. The dose equivalents and H*(10)-to-fluence ratios are also estimated. All these quantities are automatically obtained from the program. The neutron yield and the dose equivalent for ⁹Be(p, n) reaction are found to be about 4 times higher than that for ¹²C(p, n) reaction. The present methodology for neutron spectrum generation is found to be simple and effective and does not involve the complex spectrum unfolding procedures.