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تسجيل مستخدم جديدSequential fissions of heavy nuclear systems
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In Xe+Sn central collisions from 12 to 20 MeV/A measured with the INDRA 4$pi$ multidetector, the three-fragment exit channel occurs with a significant cross section. In this contribution, we show that these fragments arise from two successive binary splittings of a heavy composite system. Strong Coulomb proximity effects are observed in the three-fragment final state. By comparison with Coulomb trajectory calculations, we show that the time scale between the consecutive break-ups decreases with increasing bombarding energy, becoming compatible with quasi-simultaneous multifragmentation above 18 MeV/A.
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The theoretical approach to a sequential heavy ion double charge exchange reaction is presented. A brief introduction into the formal theory of second-order nuclear reactions and their application to Double Single Charge Exchange (DSCE) reactions by
distorted wave theory is given, thereby completing the theoretical background to our recent work [1]. Formally, the DSCE reaction amplitudes are shown to be separable into superpositions of distortion factors, accounting for initial and final state ion--ion interactions, and nuclear matrix elements. A broad space is given to the construction of nuclear DSCE response functions on the basis of polarization propagator theory. The nuclear response tensors resemble the nuclear matrix elements of $2 ubetabeta$ decay in structure but contain in general a considerable more complex multipole and spin structure. The QRPA theory is used to derive explicit expressions for nuclear matrix elements (NMEs). The differences between the NME of the first and the second interaction vertexes in a DSCE reaction is elucidated. Reduction schemes for the transition form factors are discussed by investigating the closure approximation and the momentum structure of form factors. DSCE unit strength cross sections are derived.
Kinetic energy spectra and fragment velocity correlations, simulated by means of stochastic mean-field calculations, are successfully confronted with experimental data for single multifragmenting sources prepared at the same excitation energy per nuc
leon in 32 AMeV 129Xe+natSn and 36 AMeV 155Gd+natU central collisions. Relying thus on simulations, average freeze-out times of 200-240 fm/c are estimated The corresponding spatial distributions of fragments are more compact for the lighter system (~3-4V_0 vs ~8V_0).
The Daejeon16 two-nucleon interaction is employed in many-body approaches based on the mean-field approximation. The perturbative character of Daejeon16 is verified by comparing results for 16O from the Hartree-Fock (HF) approximation and from the no
-core shell model and by examining the magnitude of perturbative corrections to the HF energy in light and heavy nuclei. In order to approximately describe energies and radii across the nuclear chart, a phenomenological correction in the form of a two-plus-three-nucleon contact interaction is introduced. With fitted parameters we achieve a very good description of medium-mass nuclei in terms of energy and size and also in terms of the centroid energy of the giant monopole resonance and the dipole polarizability calculated within the random-phase approximation (RPA). Our results provide further justification for the use of Daejeon16 augmented with phenomenological corrections as an effective interaction of perturbative character in a variety of applications.
Intermediate-energy heavy-ion collisions can produce a spin polarization of the projectile-like species. Spin polarization has been observed for both nucleon removal and nucleon pickup processes. Qualitative agreement with measured spin polarization
as a function of the momentum of the projectile-like fragment is found in a kinematical model that considers conservation of linear and angular momentum and assumes peripheral interactions between the fast projectile and target. Better quantitative agreement was reached by including more realistic angular distributions, de-orientation caused by gamma-ray emission, and by correcting for the out-of-plane acceptance. The newly introduced corrections were found to apply to both nucleon removal and nucleon pickup processes.
Exposures of test samples of nuclear track emulsion were analyzed. Angular and energy correlations of products originating from the thermal-neutron-induced reaction n$_{th} + ^{10}$B $rightarrow ^{7}$Li $+ (gamma) + alpha$ were studied in nuclear tac
k emulsions enriched in boron. Nuclear track emulsions were also irradiated with $^{86}$Kr$^{+17}$ and $^{132}$Xe$^{+26}$ of energy about 1.2 MeV per nucleon. Measurements of ranges of heavy ions in nuclear track emulsions made it possible to determine their energies on the basis of the SRIM model. The formation of high-multiplicity nuclear stars was observed upon irradiating nuclear track emulsions with ultrarelativistic muons. Kinematical features studied in this exposure of nuclear track emulsions for events of the muon-induced splitting of carbon nuclei to three alpha particles are indicative of the nuclear-diffraction interaction mechanism.
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