Fig. 1-7 Emission probability of a proton for each energy and angle from proton-nickel reaction Ep' denotes the emission energy of a proton multiplied successively with one hundred for each emission energy to avoid overlapping.

Fig. 1-8 Distribution of residual nuclei from proton-iron reaction

The nucleus, an object which is located at the center of an atom, is composed of protons, neutrons and pions held together by nuclear forces. When an accelerated particle impinges on the nucleus, several kinds of nuclear reactions occur. It is rather easy to calculate such reaction processes when an incident particle collides with only one nucleon in the nucleus or when it is captured and a statistical equilibration is accomplished. On the other hand, it has been very hard to calculate with any theoretical model the multi-step reactions where an incident particle collides with several nucleons in the nucleus. We are investigating such multi step processes using the QMD model, which is a kind of molecular dynamics method adapted to nuclear reactions. Fig. 1-7 shows the calculated and experimental proton angular distributions for each outgoing energy when a 120 MeV proton impinges on a nickel target. Fig. 1-8 shows the calculated and experimental cross sections of reaction residues when a 1.5 GeV proton impinges on an iron target. The backward scattering part of Fig. 1-7 and the yield of masses around 40 in Fig. 1-8 are the results of more than a 5-step multiple scattering. Our QMD model can reproduce the various reactions systematically without using a fitting parameter and thus we have a deeper understanding of the multi-step nuclear reactions.

Reference K. Niita et al., Analysis of the (N, x N') Reactions by Quantum Molecular Dynamics Plus Statistical Decay Model, Phys. Rev. C 52, 2620 (1995).

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