V.P. Likhachev

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.

Response function of a germanium detector to photon energies between 6 and 120 keV

Abstract We have developed a function to describe the response of an 8-cm3 germanium detector to photon energies as low as 6 keV, going up to 120 keV. Detection effects like the Ge X-ray escape and Compton scattered photons in the neighborhood of the detector were treated. This study was based on the fit of analytic functions to the features of the experimental spectra, thus revealing the parameters and their dependence on the photon energy. Our response function has 13 parameters and its validity is shown by the reproduction of the parameter-generating spectra and through the independent fit of an 152Eu spectrum.

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.

Tagged bremsstrahlung polarization: A Monte-Carlo approach

Abstract We present a Monte-Carlo approach for the determination of the degree of polarization of tagged bremsstrahlung. Our method allows the evaluation of the Bethe-Heitler expression in the photon-oriented reference system, while defining the photon and electron collimators in the spectrometer coordinate system. This avoids the need to perform fourfold integrals of complicated and bulky expressions. We reproduced the published calculations and measurements, and studied the polarization behavior as a function of several parameters in different geometric conditions.

SILICON STRIP DETECTORS FOR FISSION

Abstract The performance of a silicon strip detector especially designed for photofission experiments and a particular arrangement for low count rate photofission measurements are presented. Other applications for the same detection system are discussed.

Radiation interaction with DNA

We developed a model to describe the radiation-DNA interaction in water solution. The model is based on some important aspects of the Bethe Theory for the ionizing process, and on the assumption that the direct interaction between the incident particle and the DNA molecule is negligible in comparison with the indirect effect. This assumption can always be true under controlled conditions. The results show that the number of damages induced by radiation depends on the accumulated dose, on parameters related only to the medium properties, and on the DNA structure, but not on the incident particle. A few applications of the model are discussed, and results are successfully compared with experimental data. New experiments are proposed.

Geometrical parameters of a detection system: A Monte Carlo approach

Abstract This work presents a method for the evaluation of dynamic coincidence solid angles for 2π-detector arrangements with large illuminated target area or volume, based on Monte Carlo simulation. Particular constructions useful for photonuclear experiments, using film and gas targets, are considered.

Study of neutron-DNA interaction at the IPEN BNCT research facility

Our group at the Laboratorio do Acelerador Linear (IFUSP- USP) is currently developing several studies related to the interaction of different kinds of radiation with DNA. Initially, our plan is to study the interactions proton-DNA, gamma-DNA and neutron-DNA. In this work we describe the most important features of the neutron-DNA study, which we plan to perform by selecting thermal, epithermal and fast neutrons. To improve the information about radiation-DNA interaction is important in order to achieve more secure and efficient cancer treatments by using radiation therapy. Nowadays, one important technique is the boron neutrons capture therapy, where neutrons are used to initiate a nuclear reaction at the tumor site. The effects of the neutrons on the health tissue, however, must be better understood. The study of neutron-DNA interaction, in this scenario, is of great importance. The research facility for Boron Neutron Capture Therapy (BNCT) in the IEA-R1 Reactor of the IPEN-CNEN/SP[1] will be used for studying the neutron-induced DNA damage. At present, we are evaluating the characteristics of the neutron flux at the biological sample, and we are carrying out simulations of the experimental procedure through Monte Carlos N Particle transport code system version 4C (MCNP-4C)[2] to find the experimental conditions necessary to minimize such contamination, and also verify the effects of those gammas on the DNA molecule. The first step is the selection of filters configurations, which will allow us to irradiate the DNA sample with thermal, epithermal and fast neutrons. We present the results of our simulations, and describe the experimental setup show the best sets of materials necessary to obtain neutron spectra for different neutrons energies.

Photoneutron multiplicities of preactinide nuclei at energies above the pion threshold

Abstract The average photoneutron muliplicities ν of Au, Ta and 182 W were deduced from their previously measured excitation energies E x , from 160 to 250 MeV. A combined analysis of these data and those measured at Saclay up to 140 MeV allowed the extraction of information on E x at the “pure evaporation” and quasideuteron energy regions. A theoretical approach for the study of ν above 140 MeV, which incorporates photopion reabsorption processes by two-body, was proposed, allowing a tentative delineation of the pion mean free path in the nucleus.

Excitation of discrete levels in 54Fe and 56Fe nuclei by means of (e, e′) reactions

The excitation of discrete levels in 54Fe and 56Fe nuclei by means of (e, e′) reactions is studied at excitation energies of up to 8 MeV over the momentum-transfer range between 0.6 and 1.7 fm−1. An unconventional procedure of multipole analysis is used in experimental-data processing. Data on the reduced probability of transitions and their multipolarity are obtained for 12 low-lying levels of 54Fe and 10 levels of 56Fe. Five levels in 54Fe and three levels in 56Fe are observed for the first time in (e, e′) reactions. There is no information about two of them in the present-day database on discrete levels.