J. Mesa

BARRIER code : calculation of fission barriers

Abstract Average values of various nuclear properties are only explained on average by the liquid drop model ( where the average might be taken over particle number or, alternatively, over deformation). To reproduce other aspects of nuclear structure, such as ground state spins and energy spectra, it was found elsewhere that a different description is necessary. In this regard, we calculated single particle energies as function of the deformation parameters of an axially deformed Woods-Saxon potential, as input to the shell correction calculations. To obtain the total nuclear energy, it is also necessary to add a pairing energy in order to take into consideration the short range nuclear interactions, which are not taken into account in the mean field approximation. Many works found in the literature deal with potential energy surface and calculated mass by using the Strutinsky method. Bjornholm and Lynn pointed out the impact caused by an adequate description of parametrization in each calculation. In particular, many details in the description of fission processes like fission isomers and angular distribution are sensitive to the choice of the parametrization. Some previous works pointed out the advantages of Cassini ovaloid parametrization for very deformed shape calculations. The numerical code BARRIER, proposed and used in this work, calculates the potential energy surface in the Strutinsky semi-microscopical approach using the Cassini ovaloid shape parametrization for the nuclear potential.

Transfer coefficient measurements of uranium to the organs of Wistar rats, as a function of the uranium content in the food.

Groups of animals (Wistar rats) were fed with rations doped with uranyl nitrate at concentrations ranging from 0.5 to 100 ppm. The uranium content in the ashes of the organs was measured by the neutron-fission track counting technique. The most striking result is that the transfer coefficients, as a function of the uranium concentration, exhibit a concave shape with a minimum around 20 ppm-U for all organs. Explanations to interpret this finding are tentatively given.

A new statistical method for transfer coefficient calculations in the framework of the general multiple-compartment model of transport for radionuclides in biological systems

A new and simple statistical procedure (STATFLUX) for the calculation of transfer coefficients of radionuclide transport to animals and plants is proposed. The method is based on the general multiple-compartment model, which uses a system of linear equations involving geometrical volume considerations. By using experimentally available curves of radionuclide concentrations versus time, for each animal compartment (organs), flow parameters were estimated by employing a least-squares procedure, whose consistency is tested. Some numerical results are presented in order to compare the STATFLUX transfer coefficients with those from other works and experimental data.

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.

Quasi-free 238U(e,e′f) cross section in macroscopic–microscopic approach

We present the result of a theoretical study of inclusive quasi-free electrofission of 238U. The off-shell cross sections for the quasi-free reaction stage have been calculated within the Plane Wave Impulse Approximation (PWIA) using a macroscopic–microscopic description of the proton and neutron single particle momentum distributions. Electron wave function distortion corrections were included using the effective momentum approximation. The fissility for the proton single hole excited states of the residual nucleus 237Pa was calculated both with and without contributions of the pre-equilibrium emission of the particles. The fissility of the 237,238U residual nuclei was calculated within the compound nucleus model. Final state interaction correction to the fissility was calculated using a pure imaginary optical potential. The (e,e′f) cross sections, thus obtained, were compared with available experimental data.We present the result of a theoretical study of inclusive quasi free electrofission of

OMEGA code : calculation of the geometrical parameters of detection systems

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LINDEN: Code for level density calculations of deformed nuclei using Lipkin–Nogami projectors in the BCS approach

U. The off-shell

Long-term accumulation of uranium in bones of Wistar rats as a function of intake dosages.

cross sections for the quasi free reaction stage have been calculated within the Plane Wave Impulse Approximation (PWIA), using a Macroscopic -Microscopic description of the proton and neutron single particle momentum distributions. Electron wave function distortion corrections were included using the effective momentum approximation, and the Final State Interaction (FSI) effects were calculated using an optical potential. The fissility for the proton single hole excited states of the residual nucleus

Woods-Saxon potential parametrization at large deformations for plutonium odd isotopes

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