S.B. Duarte

The CRISP package for intermediate- and high-energy photonuclear reactions

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–Sao 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 MCEF code for nuclear evaporation and fission calculations

We present an object oriented algorithm, written in the Java programming language, which performs a Monte Carlo calculation of the evaporation-fission process taking place inside an excited nucleus. We show that this nuclear physics problem is very suited for the object oriented programming by constructing two simple objects: one that handles all nuclear properties and another that takes care of the nuclear reaction. The MCEF code was used to calculate important results for nuclear reactions, and here we show examples of possible uses for this code.

A Monte Carlo method for nuclear evaporation and fission at intermediate energies

Abstract We describe a Monte Carlo method to calculate the characteristics of the competition between particle evaporation and nuclear fission processes taking place in the compound nucleus formed after the intranuclear cascade following the absorption of intermediate energy photons by the nucleus. In this version we include not only neutrons, but also protons and alphas as possible evaporating particles. The present method allows the easy inclusion of other evaporating particles, such as deuteron or heavier clusters. Some fissility results are discussed for the target nuclei 237 Np, 238 U and 232 Th.

PHOTONUCLEAR K+ PRODUCTION CALCULATION NEAR THRESHOLD

Abstract Photonuclear kaon production near threshold is investigated as a function of incident energy and the target-nucleus mass, by using the intranuclear cascade model. The present calculation shows that the residual nuclei produced in coincidence with kaons are hotter than those obtained by averaging the excitation energy over inclusive γ -nucleus events. We note that the experimental differential cross section for 12 C( γ ,K + ) is well reproduced within the present model.

Fragment mass distributions in the fission of heavy nuclei by intermediate- and high-energy probes

Recent experiments have shown that the multimode approach for describing the fission process is compatible with the observed results. A systematic analysis of the parameters obtained by fitting the fission-fragment mass distribution to the spontaneous and low-energy data has shown that the values for those parameters present a smooth dependence upon the nuclear mass number. In this work, a new methodology is introduced for studying fragment mass distributions through the multimode approach. It is shown that for fission induced by energetic probes ( E> 30 MeV) the mass distribution of the fissioning nuclei produced during the intranuclear cascade and evaporation processes must be considered in order to have a realistic description of the fission process. The method is applied to study 208 Pb, 238 U, 239 Np and 241 Am fission induced by protons or photons.

Nucleon effective mass effects on the Pauli-blocking function

The effects of nucleon effective mass on the Pauli-blocking function are worked out. We have shown that such effects on the quasi-deuteron mechanism of photonuclear absorption are rather relevant. The Pauli-blocking function has been evaluated by applying a Monte Carlo calculation particularly suitable for simulation of intranuclear cascade processes of intermediate-energy nuclear reactions. The nucleon binding in the photonuclear absorption mechanism is taken into account accordingly.

Nuclear photofissility of natPb and 232Th at energies above the pion photoproduction threshold

A new, simple approach based on the intranuclear cascade plus the evaporation–fission competition mechanisms of photonuclear reactions has been developed to calculate fissility values at energies above ~200 MeV. This approach has been successfully used in explaining fissility data for natPb and 232Th target nuclei at energies up to 3.8 GeV recently obtained at the Thomas Jefferson Laboratory. Predictions of photofissility up to 5–6 GeV for these nuclei are also given.

Hot hypernucleus formation in high-energy photonuclear reactions

The probability of a compound residual hot hypernucleus formation at the end of pre-equilibrium phase of high energy photonuclear reactions is calculated with a time dependent Monte Carlo Multicollisional Cascade (MCMC) approach. The emission of hadrons during the rapid phase of the reaction is discussed and characteristics of the residual nucleus are obtained. Results for mass and charge distributions of the formed hot hypernucleus are shown and its excitation energy is discussed.

New approach to nuclear photofission reactions above 0.15 GeV

A simple approach to evaluate nuclear photofissilities at energies above the pion photoproduction threshold has been developed. It is based on the current, two-step model for intermediate-energy photonuclear reactions, i.e. a photon-induced intranuclear cascade followed by a fission-evaporation competition process for the excited, post-cascade residual nucleus. The calculation method (semiempirical by nature) shows that fissility (i.e., total fission probability) is governed by two basic quantities, namely, the first-chance fission probability for the average cascade residual, and a parameter which defines an evaporative sequence of residuals in which the average, equivalent chance-fission probabilities of nuclides belonging to the same generation are located. The natPb photofissility data measured recently in the range ~ 0.2 - 3.8 GeV at the Thomas Jefferson Laboratory could be explained very satisfactorily by the present approach.

Photofissility at 1 GeV for nuclei throughout the periodic table

A new approach to evaluate nuclear photofissilities at incident photon energies above the pion photoproduction threshold has been recently developed and proved to describe successfully the fissilities of natPb and 232Th target nuclei at energies ~0.2-4.0 GeV. The method is merely a simple, semiempirical description of the photofission reactions in which fissility, f, is governed by two basic quantities, namely, i) the first-chance fission probability,