The role of various mechanisms in formation of inclusive spectra of reactions (P,XP) on 204,20'7Pb and 120Sn

Full text: Working out the pre-equilibrium decay mechanism in nuclear reactions, which reflects the dynamics of the formation of the excited system and its evolution to the equilibrium state, remains an actual problem of the nuclear reaction theory. These reactions play a role in the applied researches on secure and wasteless nuclear power system creation. The inclusive spectra of protons emitted from proton induced reactions on 204,207Pb and 120Sn isotopes at Ep=29.9 0.1 MeV in angular range 30-135 deg with the step 15 deg have been measured on isochronous cyclotron U-150M of Institute of Nuclear Physics. We obtained the experimental integral spectra by integrating the double-differential cross-sections on angle. Many different theoretical approaches have been used to describe the preequilibrium reaction data over a wide range of incident energies. In this work, the analysis of the experimental results has been conducted in the Griffin exciton model [1] of the preequilibrium decay of nuclei. The program PRECO-D2 [2], which describes the emission of particles with mass numbers from 1 to 4, has been used in our theoretical calculations. The Griffin exciton model is a statistical model, which describes the excited levels of the intermediate system in terms of the single-particle shell model, i.e., characterized by the number of the excited particles (above the Fermi level) and holes (below the Fermi level). From comparison of experimental and calculated integral spectra, it follows that main contribution in hard part of total cross section is due to multi-step direct (MSD) reaction mechanism. It is also shown that evaporated part of cross-section is underestimated in framework of used version of exciton model. References: 1. J. J.Griffin, Phys. Rev. Lett. 17(1966) 478.; 2. C.Kalbach, 'PRECO-D2: Program for Calculating Pre-equilibrium and Direct Reaction Double Differential Cross Sections', LA-10248-MS (February 1985). (authors)