Production Of Neutron-rich Nuclei Research Articles

Production of neutron-rich nuclei in the vicinity of 78Ni: Fragmentation reactions of unstable 81Ga and 82Ge beams

The fragmentation reactions of neutron-rich unstable nuclei 81Ga and 82Ge at 250 MeV/nucleon have been studied in order to search the optimal mean for the production of very neutron-rich nuclei in the vicinity of 78Ni. The newly measured cross sections were compared with various calculations, showing a good agreement with EPAX3.01. The present work provides experimental insights into the two-step scheme—fragmentation following fission—as a method to produce very neutron-rich nuclei through a combination of ISOL and fragmentation of post-accelerated beams of unstable nuclei. Our results enable an evaluation of the potential of the two-step scheme in the production of very neutron-rich nuclei for the 78Ni region. The two-step scheme using fragmentation of a post-accelerated 81Ga beam could be an option to produce neutron-rich nuclei around 78Ni when the 81Ga beam intensity reaches 1.0×108 pps, compared to the one-step scheme with fission of 238U.

Influence of the incident energy of the projectile and of different targets on the production of neutron-rich nuclei

The multinucleon transfer reaction is treated as a diffusion process by solving four-variable master equations within the dinuclear system (DNS) concept. The reaction systems $^{136}\mathrm{Xe}+^{208}\mathrm{Pb}$ and $^{136}\mathrm{Xe}+^{198}\mathrm{Pt}$ are investigated and compared to the experimental data. The calculated results correctly describe the magnitude and maxima of the observed transfer cross sections for a wide range of transfers. One finds that the neutron richness of the reaction products is strongly dependent on the projectile energy near the Coulomb barrier. By comparing the obtained results for the above two reaction systems, the absolute cross sections from the $^{208}\mathrm{Pb}$ target predict smaller production cross sections for neutron-deficient nuclei and moderately neutron-rich nuclei as compared to $^{198}\mathrm{Pt}$.

Microscopic predictions for the production of neutron-rich nuclei in the reaction Yb176 + Yb176

Background: Production of neutron-rich nuclei is of vital importance to both understanding nuclear structure far from stability and to informing astrophysical models of the rapid neutron capture process (r-process). Multinucleon transfer (MNT) in heavy-ion collisions offers a possibility to produce neutron-rich nuclei far from stability. Purpose: The $^{176}\mathrm{Yb}+{}^{176}\mathrm{Yb}$ reaction has been suggested as a potential candidate to explore the neutron-rich region surrounding the principal fragments. The current study has been conducted with the goal of providing guidance for future experiments wishing to study this (or similar) system. Methods: Time-dependent Hartree-Fock (TDHF) and its time-dependent random-phase approximation (TDRPA) extension are used to examine both scattering and MNT characteristics in $^{176}\mathrm{Yb}+{}^{176}\mathrm{Yb}$. TDRPA calculations are performed to compute fluctuations and correlations of the neutron and proton numbers, allowing for estimates of primary fragment production probabilities. Results: Both scattering results from TDHF and transfer results from the TDRPA are presented for different energies, orientations, and impact parameters. In addition to fragment composition, scattering angles and total kinetic energies, as well as correlations between these observables are presented. Conclusions: $^{176}\mathrm{Yb}+{}^{176}\mathrm{Yb}$ appears to be an interesting probe for the mid-mass neutron-rich region of the chart of nuclides. The predictions of both TDHF and TDRPA are speculative, and will benefit from future experimental results to test the validity of this approach to studying MNT in heavy, symmetric collisions.

Effect of isospin diffusion on the production of neutron-rich nuclei in multinucleon transfer reactions

The isospin dissipation dynamics in multinucleon transfer reactions has been investigated within the dinuclear system model. Production cross sections of neutron-rich isotopes around projectile-like and target-like fragments are estimated in collisions of $^{58,64}\mathrm{Ni}+^{208}\mathrm{Pb}$ and $^{78,86,91}\mathrm{Kr}+^{198}\mathrm{Pt}$ near Coulomb barrier energies. The isospin diffusion in the nucleon transfer process is coupled to the dissipation of relative motion energy and angular momentum of colliding system. The available data of projectile-like fragments via multinucleon transfer reactions are nicely reproduced. It is found that the light projectile-like fragments are produced in the neutron-rich region because of the isospin equilibrium in two colliding nuclei. However, the heavy target-like fragments tend to be formed on the neutron-poor side above the $\ensuremath{\beta}$-stability line. The neutron-rich projectiles move the maximal yields of heavy nuclei to the neutron-rich domain and are available for producing the heavy exotic isotopes, in particular around the neutron shell closure of $N=126$.

Production of neutron-rich nuclei approaching r-process by gamma-induced fission of 238U at ELI-NP

The investigation of neutron-rich exotic nuclei is crucial not only for nuclear physics but also for nuclear astrophysics. Experimentally, only few neutron-rich nuclei near the stability have been studied, however, most neutron-rich nuclei have not been measured due to their small production cross sections as well as short half-lives. At ELI-NP, gamma beams with high intensities will open new opportunities to investigate very neutron-rich fragments produced by photofission of 238U targets in a gas cell. Based on some simulations, a novel gas cell has been designed to produce, stop and extract 238U photofission fragments. The extraction time and efficiency of photofission fragments have been optimized by using SIMION simulations. According to these simulations, a high extraction efficiency and a short extraction time can be achieved for 238U photofission fragments in the gas cell, which will allow one to measure very neutron-rich fragments with short half-lives by using the IGISOL facility proposed at ELI-NP.

Yields of neutron-rich nuclei by actinide photofission in the giant dipole resonance region

Photofission of actinides is studied in the region of nuclear excitation energies that covers the entire giant dipole resonance (GDR) region. A comparative analysis of the behavior of the symmetric and asymmetric modes of photon induced fission as a function of the average excitation energy of the fissioning nucleus is performed. The mass distributions of $^{238}$U photofission fragments are obtained at the endpoint bremsstrahlung energy of 29.1 MeV which corresponds to mean photon energy of 13.7$\pm$0.3 MeV that coincides with GDR peak for $^{238}$U photofission. The integrated yield of $^{238}$U photofission as well as charge distribution of photofission products are calculated and its role in the production of neutron-rich nuclei and their exoticity is explored.

Production of Neutron-rich Nuclei in Low-energy Multinucleon Transfer Reactions

Production of Neutron-rich Nuclei in Low-energy Multinucleon Transfer Reactions

Production of neutron-rich nuclei in fragmentation reactions of [formula omitted] projectiles at relativistic energies

The fragmentation of neutron-rich Sn132 nuclei produced in the fission of U238 projectiles at 950 A MeV has been investigated at the FRagment Separator (FRS) at GSI. This work represents the first investigation of fragmentation of medium-mass radioactive projectiles with a large neutron excess. The measured production cross sections of the residual nuclei are relevant for the possible use of a two-stage reaction scheme (fission+fragmentation) for the production of extremely neutron-rich medium-mass nuclei in future rare-ion-beam facilities. Moreover, the new data will provide a better understanding of the “memory” effect in fragmentation reactions.

Superasymmetric fission at intermediate energy and production of neutron-rich nuclei with A < 80

Abstract The yields of neutron-rich Ni, Cu, Zn, Ga and Ge-isotopes were measured in 25 MeV proton induced fission of 238 U using the ion guide-based isotope separator technique. The results indicate enhancement for superasymmetric mass division at intermediate excitation energy of the fissioning nucleus and show the potential of this reaction for the production of neutron-rich exotic nuclei around Z = 28.

Mass and charge distributions of Cl-induced heavy-ion reactions.

Projectilelike fragments were detected and characterized in terms of A, Z, and energy for the reactions $^{37}\mathrm{Cl}$ on $^{40}\mathrm{Ca}$ and $^{209}\mathrm{Bi}$ at E=7.3 MeV/nucleon, and $^{35}\mathrm{Cl}$ on $^{209}\mathrm{Bi}$ at E=15 MeV/nucleon, at angles close to the grazing angle. Mass and charge distributions were generated in the N-Z plane as a function of energy loss, and parametrized in terms of their centroids, variances, and coefficients of correlation. The results are compared to the predictions of two current models based on a stochastic nucleon exchange mechanism. The drifts of the charge and mass centroids for the system $^{37}\mathrm{Cl}$ on $^{40}\mathrm{Ca}$ are consistent with a process of mass and charge equilibration mediated by nucleon exchange between the two partners, followed by evaporation. The asymmetric systems show a strong drift toward larger asymmetry, with the production of neutron-rich nuclei. It is concluded that this is the result of a net transfer of protons from the light to the heavy partner, and a net flow of neutrons in the opposite direction. Model predictions fail to reproduce in detail the evolution of the centroids for asymmetric systems. The variances for all systems increase with energy loss, as would be expected from a nucleon exchange mechanism. However, the variances for the reaction $^{37}\mathrm{Cl}$ on $^{40}\mathrm{Ca}$ are higher than those expected from that mechanism, and the variances for the reaction $^{35}\mathrm{Cl}$ on $^{209}\mathrm{Bi}$ start decreasing after about 100 MeV of energy loss. The coefficients of correlation indicate that the transfer of nucleons between projectile and target is correlated, as expected from Q-value constraints to the valley of \ensuremath{\beta} stability.

Production of neutron rich nuclei by fragmentation of 760 A·MeV 136Xe

The fragmentation of 760 A·MeV 136Xe projectiles impinging on a 27Al target has been investigated at the fragment separator FRS at GSI Darmstadt. Production cross sections for neutron rich nuclei in the 116 ≤ A ≤ 134 mass region have been determined and are compared to an empirical parametrisation as well as to model calculations. For the double magic nucleus 132Sn we extrapolate σ ≅ 0.4 ± 0.3 μbarn.

Production of neutron-rich nuclei at the limits of particles stability by fragmentation of [formula omitted] projectiles

In-flight identification of fragments from 44 MeV u 40 Ar emitted at 0° provides the first experimental observation of 23 N, 29 Ne and 30 Ne . On the other hand 18 B, 21 C and 25 O are found to be particle-instable.

Calculation of nuclide distributions in deep inelastic scattering and the production of neutron rich nuclei

Nuclide distributions for deep inelastic fragments are calculated considering the diffusion of the intermediate dinuclear system in a two-dimensional liquid drop potential energy surface. Particle decay from the fragments is taken into account by statistical model calculations. The concept of charge equilibration is investigated. Calculations are compared to previously measured nuclide distributions. Predictions are made for the production cross sections of neutron-rich nuclei in deep inelastic reactions.