An analysis of the quasielastic and inelastic peaks of neutrons induced by 1.2 GeV protons on targets with 27⩽A⩽232 is presented using the ultrarelativistic quantum molecular dynamics (UrQMD) model. Two distinct contributions of the nuclear medium are studied in the UrQMD framework, referred to as “in-medium” and “mean field” effects. The former only includes modifications to the NN-elastic and NN→NΔ angular distributions as well as changes to the Δ-mass distribution. The latter incorporates the (QMD) interaction potential between nucleons. It is shown that in-medium effect produces an important role for enhancing the quasi-inelastic peak, while the mean field effect enhances the intensity of both peaks and becomes important in the quasielastic region. The introduction of both effects in the UrQMD calculations improves the intensity and location of the quasielastic and inelastic peaks. A rather smooth dependence of the integrated cross sections of the quasielastic and inelastic peaks on the mass number at both angles is also found and shown to be in qualitative agreement with the UrQMD incorporating these two effects.