The two-step process that characterizes the intermediate-and high-energy photonuclear reactions (between 40 MeV and 4 GeV) has been successfully described by Monte Carlo calculations. Recently, a new class of codes capable to perform those calculations according to a more realistic method has been developed, improving the possibilities for simulating the reactions in more details. In this work we present the CRISP package (standing for Rio-São Paulo Collaboration), which is a coupling of the multi collisional Monte Carlo (MCMC) and the Monte Carlo for evaporation-fission (MCEF) codes. The first one describes the intranuclear cascade process, while the second one is dedicated to the evaporation/fission competition step. Both codes have already shown to be useful for calculating several features of different nuclear reactions. The CRISP code, coupling these two software, represents a good tool to describe the complex characteristics of the nuclear reactions, and opens the opportunity for applications in quite different fields, such as studies of hadron physics inside the nucleus, specific nuclear reactions, spallation and/or fission processes initiated by different probes and many others.
The energy dependence of photofission cross section for heavy nuclei has recently been well described in terms of a Monte Carlo calculation at energies from the pion photoproduction threshold up to 1 GeV [see, for instance, A. Deppman et al., Phys. Rev. Lett. 87 (2001) 182701]. Recent experimental data from CLAS (CEBAF Large Angle Spectrometer) collaboration have extended the measured photofission cross section up to 3.5 GeV for actinide and preactinide nuclei. In this work we address the calculation of photoabsorption and photofission cross sections for actinide and preactinide nuclei above 1 GeV, a region where the shadowing effect plays an important role in the nuclear photoabsorption process. DOI: 10.1103/PhysRevC.73.064607 PACS number(s): 25.20.−x, 25.85.Jg, 24.10.Lx, 24.85.+p Photon-nucleus reactions are excellent tools for investigating nuclear and nucleonic structures. The photonuclear absorption process, for instance, has been used to study the formation and propagation of baryonic resonances inside nuclear matter [1-6], the photon hadronization process that gives rise to the shadowing effect in the photoabsorption cross section [1,7], or the formation and propagation of hyperons in the nucleus [6]. The simplicity of photonuclear reactions as compared to reactions induced by other probes, from both the theoretical and experimental points of view, is attractive to those willing to study nuclear and subnuclear structures.However, the various nuclear processes taking place during the reaction, mainly at intermediate and high energies, cause some problems in the comprehension of the nuclear or subnuclear mechanisms. One example is the fissility of heavy nuclei. It was supposed that fissility was an increasing function of the photon energy, and that for actinide nuclei, which present the highest fissility values among the stable nuclei, one could expect their fissility to be 1 for energies above a few hundred MeV [8]. In fact, the measurement of fission cross section was proposed as a reliable method for measuring the total photoabsorption cross section [9,10]. A fine, although incomplete, overview on the theoretical approaches for calculating photofission cross sections is presented in Ref. [11].Experimental results obtained at Frascati [9,10], Mainz [12,13], Bonn [1,14], Saskatoon [15], and Thomas Jefferson Laboratory [16,17] have shown, however, that this was not the case. The fissility for thorium and several uranium isotopes was found to be lower than that for neptunium, showing that nuclear fissility does not saturate for those nuclei, remaining at a value below 100% even at high incident photon energies. This result was fully explained by a Monte Carlo study of the intranuclear cascade and evaporation/fission competition processes that follows the photon absorption, as implemented by the MCMC and MCEF codes [18,19]. The important feature for explaining the nonsaturation of the heavy-nuclei fissility was the inclusion of protons and α-particles evaporation in the evaporation-fission competition proc...
This paper reviews the physics of the spallation which is a nuclear reaction in which a particle (e.g. proton) interacts with a nucleus. Given to the high energy of the incident proton, in a first stage it interacts with the individual nucleons in an intranuclear cascade which leads to the emission of secondary particles (neutrons, protons, mesons, etc.). In a secondary stage the nucleus is left in an excited state and can de-excite by evaporation and/or fission. Given to the high number of secondary neutrons produced (∼30 n/p for proton energy of 1 GeV), this reaction can be used as a source of neutrons, for example for ADS systems as external source to drive the sub critical reactor. The main codes used in the ADS target design and an example on the utilization of one of these codes (the LAHET code) for typical ADS target are given.
One of the main applications of the Hybrid Reactors (ADS -Accelerator Driven System) is the incineration of transuranics (TRU) by fast neutrons that emerge from a spallation source in a sub critical reactor waste burner [1,2]. For this application, an accurate description and prediction of spallation reaction is necessary, including all the characteristics concerning spatial and energetic angular distributions, spallation products and neutron multiplicity. To describe the nuclear reactions at intermediate and high energies, Monte Carlo calculations have been used. The CRISP package considers the intranuclear cascade (INC) that occurs during the spallation process in a realistic time-sequence approach in which all particles inside the nucleus can participate in the cascade and the nuclear density fluctuations are naturally taken into account during the process. The occupation number of each single particle level is considered as a function of time and a more realistic Pauli blocking mechanism can be performed. None of the existing models have effectively used all those features. The evaporation of protons and alpha particles are taken into account making possible the correct prediction of fissilities of actinides and pre-actinides [3]. Another implementation is the NN single-pion production reaction. This reaction is especially relevant if one is interested in neutron or proton multiplicities, since the creation/emission of pions is directly related with the excitation energy of the residual nucleus. We will present some results obtained with the CRISP package for proton-nucleus reaction at intermediate and high energies. This package was obtained by the coupling of the MCMC [4] and MCEF [5] codes, with the introduction of some improvements, such as better Pauli blocking mechanism, which constrains the residual nucleus energetic evolution to the Pauli Principle from the ground-state to the final compound-nucleus formed at the end of the intranuclear cascade process, and introduction of the most relevant resonant excitation and the NN single pion production channel. The results of interest for ADS development are consistent with the experimental data at different proton energies. More detailed calculations are being performed for studying other features of proton-nucleus reactions and with different targets.
The (W, Q 2 ) dependence of the ratio of inclusive electron scattering cross sections for 15 N/ 12 C was determined in the kinematic ranges 0.8 < W < 2 GeV and 0.2 < Q 2 < 1 GeV 2 using 2.285 GeV electrons and the CLAS detector at Jefferson Lab. The ratios exhibit only slight resonance structure, in agreement with a simple phenomenological model and an extrapolation of deep-inelastic scattering ratios to low Q 2 . Ratios of 4 He/ 12 C using 1.6 to 2.5 GeV electrons were measured with very high statistical precision and were used to correct for He in the N and C targets. The (W, Q 2 ) dependence of the 4 He/ 12 C ratios is in good agreement with that of the phenomenological model and exhibit significant resonance structure centered at W = 0.94, 1.23, and 1.5 GeV.
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