Relativistic mean field formulation of clustering in heavy nuclei

Very little is known about clustering in heavy nuclei and in particular the interaction between the correlated cluster nucleons and remaining core nucleons. Currently the phenomenological Saxon-Woods plus cubic Saxon-Woods core-cluster potential successfully predicts the alpha decay half-life and energy band spectra of a number of heavy nuclei. This model, however, lacks a microscopic understanding of clustering phenomenon in these heavy nuclear systems. A fully relativistic microscopic formalism is presented, which generates the core-cluster potential by means of the McNeil, Ray and Wallace based double folding procedure. The core and cluster baryon densities are calculated by using a relativistic mean field approach. The Lorentz covariant IA1 representation of the nucleon-nucleon interaction is folded with the core and cluster densities. Theoretical predictions of the ground-state decay half-life and positive parity energy band of 212Po are obtained with the relativistic mean field formalism and which are compared to the results from the phenomenological Saxon-Woods plus cubic Saxon-Wood core-cluster potential and microscopic M3Y interaction

Transition and static moments of octupole-deformed heavy nuclei

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Hybrid potential model of the α-cluster structure of Po212

Cluster-core potentials derived microscopically or phenomenologically each have some desirable features. We combine these features in an analysis of the properties of Po212 treated as an α-Pb208 system. © 2010 The American Physical Society.Articl

Hybrid potential analysis of exotic clustering in heavy nuclei

We generate a hybrid potential by combining the best features of a microscopic and a phenomenological core-cluster potential and use it to analyze the spectra, B(E2) transition rates, and the exotic decays of heavy even-even nuclei. © 2012 American Physical Society

A novel detector for high neutron flux measurements

Measuring alpha particles from a neutron induced break-up reaction with a mass spectrometer can be an excellent tool for detecting neutrons in a high neutron flux environment. Break-up reactions of 6Li and 12C can be used in the detection of slow and fast neutrons, respectively. A high neutron flux detection system that integrates the neutron energy sensitive material and helium mass spectrometer has been developed. The description of the detector configuration is given and it is soon to be tested at iThemba LABS, South Africa. © 2009 American Institute of Physics.Conference Pape

Nuclear medium modifications of the NN interaction via quasielastic (p + (Combining right arrow above sign),p + (Combining right arrow above sign)′) and (p + (Combining right arrow above sign),n + (Combining right arrow above sign)) scattering

Based on the relativistic plane-wave impulse approximation for quasielastic (p + (Combining right arrow above sign),p + (Combining right arrow above sign)′) and (p + (Combining right arrow above sign),n + (Combining right arrow above sign)) polarization observables, we provide quantitative estimates of nuclear medium modifications of the NN interaction. We employ a 40Ca target for proton energies ranging from 135 to 300 MeV at a momentum transfer of 1.97 fm-1. Compared to former calculations, we have generated new meson-exchange parameters for the relativistic NN amplitudes between 80 and 200 MeV. Finally, the results are compared to the limited available data.Articl

Relativistic predictions of spin observables for exclusive proton knockout reactions

We demonstrate the ability of complete sets of exclusive (p →,2p→) polarization transfer observables to discriminate between different model ingredients of the relativistic distorted wave impulse approximation (DWIA). Spin observables are identified, which are sensitive to Dirac versus Schrödinger dynamical equations of motion, different distorting optical potentials, finite-range versus zero-range approximations to the DWIA, as well as medium-modified meson-nucleon coupling constants and meson masses. In particular, we consider the knockout of protons from the 3s1/2, 2d3/2, and 2d5/2 states in 208Pb, at an incident laboratory kinetic energy of 202 MeV, and for coincident coplanar scattering angles (28.0°, -54.6°). The reaction kinematics are chosen so as to maximize the influence of distortion effects, while still maintaining the validity of the impulse approximation, and also avoiding complications associated with the inclusion of recoil corrections in the relativistic Dirac equation.Articl

Cluster aspects of collinear cluster tri-partition (CCT)

International audienceNew results demonstrating the so-called Ni-bump being the most populated mode of the collinear cluster tripartition (CCT) of $^{252}$Cf(sf) are presented. The physical scenario of this effect is discussed. It is tested by calculations of potential energy surfaces for the fission of the intermediate fragments formed after first rupture of the mother nucleus. Fission barriers are extracted and mass asymmetries at saddles are compared with the masses of the fission fragments that take part in the Ni-bump

Multistep direct mechanism in the (p→,3He) inclusive reaction on 59Co and 93Nb at an incident energy of 100 MeV

The inclusive (p→,3He) reactions on 59Co and 93Nb were investigated at an incident energy of 100 MeV. Emission-energy distributions for cross sections as well as analyzing powers, were measured from a threshold of ∼35 MeV, determined by the detector configuration, up to the kinematic maximum. An angular range from 15° to 140° (lab) was covered. The experimental distributions were compared with a multistep direct theory in which a reaction mechanism based on deuteron pickup is employed. Reasonable agreement between experimental double differential cross sections and analyzing powers and the theoretical expectation is obtained.Articl

Analyzing power of the Ca40(p→,pα) reaction at 100 MeV

Analyzing powers have been measured for the Ca40(p→,pα)Ar36 reaction at an incident energy of 100 MeV for coplanar scattering angles corresponding to zero recoil momentum of the residual nucleus. Predictions based on the distorted wave impulse approximation fail to reproduce the data. © 2008 The American Physical Society.Articl