Neutron-rich Rare Isotope Production Research Articles

Rare Isotope Production in peripheral heavy-ion collisions at beam energy of 15 MeV/nucleon

This paper presents our recent study on the production of neutron-rich rare isotopes with heavy-ion beams in the energy region of 15 MeV/nucleon. We present calculated production cross sections of neutron-rich nuclides from collisions of a 86Kr (15 MeV/nucleon) beam with 238U targets. Our calculations are based on a two-step approach: the dynamical stage of the collision is described with either the phenomenological Deep-Inelastic Transfer model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The de-excitation of the hot heavy projectile fragments is performed with the Statistical Multifragmentation Model (SMM). We also performed calculations with a radioactive beam of 92Kr (15 MeV/nucleon) with a target of 238U and observed that the multinucleon transfer mechanism leads to very neutron-rich nuclides toward and beyond the astrophysical r-process path. In the future, we plan to experimentally investigate such reactions in the KOBRA spectrometer at the RISP facility in Korea. We conclude that the reaction mechanism at beam energies below the Fermi energy involving periph- eral nucleon exchange, constitutes a novel and effective route to access extremely neutron-rich isotopes toward the r-process path and the neutron drip-line.

Neutron-rich rare isotope production with stable and radioactive beams in the mass range A~40-60 at 15 MeV/u

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Neutron-rich rare isotope production with stable and radioactive beams in the mass range A ∼ 40–60 at beam energy around 15 MeV/nucleon

We studied the production of neutron-rich nuclides in multinucleon transfer collisions of stable and radioactive beams (RIB) in the mass range A ∼ 40–60. We first presented our experimental cross section data of projectile fragments from the reaction of 40Ar(15 MeV/nucleon) with 64Ni, 58Ni and 27Al. We then compared them with calculations based on either the deep-inelastic transfer model or the constrained molecular dynamics model, followed by the statistical multifragmentation model. An overall good agreement of the calculations with the experimental data is obtained. We continued with calculations of the reaction of 40Ar (15 MeV/nucleon) with 238U target and then with reactions of 48Ca (15 MeV/nucleon) with 64Ni and 238U targets. In these reactions, very neutron-rich rare isotopes are produced with large cross sections. These nuclides, in turn, can be assumed to form RIB and interact with a subsequent target (preferably 238U), leading to the production of extremely neutron-rich and even new isotopes (e.g. 60Ca) in this mass range. We conclude that multinucleon transfer reactions with stable or RIB at energy around 15 MeV/nucleon offer an effective route to access extremely neutron-rich rare isotopes for nuclear structure or reaction studies.

Neutron-rich rare-isotope production from projectile fission of heavy nuclei near 20 MeV/nucleon beam energy

We investigate the possibilities of producing neutron-rich nuclides in projectile fission of heavy beams in the energy range of 20 MeV/nucleon expected from low-energy facilities. We report our efforts to theoretically describe the reaction mechanism of projectile fission following a multinucleon transfer collision at this energy range. Our calculations are mainly based on a two-step approach: the dynamical stage of the collision is described with either the phenomenological Deep-Inelastic Transfer model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The deexcitation/fission of the hot heavy projectile fragments is performed with the Statistical Mul- tifragmentation Model (SMM). We compared our model calculations with our previous experimental projectile-fission data of 238U (20 MeV/nucleon)+208Pb and 197Au (20 MeV/nucleon)+197Au and found an overall reasonable agreement. Our study suggests that projectile fission following periph- eral heavy-ion collisions at this energy range offers an effective route to access very neutron-rich rare isotopes toward and beyond the astrophysical r-process path.

Systematic study of neutron-rich rare isotope production in peripheral heavy-ion collisions below the Fermi energy

Detailed calculations of the yields of projectilelike fragments (with focus on the neutron-rich isotopes) are presented for the interaction of $^{86}\mathrm{Kr}$ (15 MeV/nucleon) with $^{64}\mathrm{Ni}$, $^{58}\mathrm{Ni}$, and $^{124}\mathrm{Sn}$, $^{112}\mathrm{Sn}$, as well as $^{86}\mathrm{Kr}$ (25 MeV/nucleon) with $^{124}\mathrm{Sn}$ and compared with our recently published experimental data for these reactions. The calculations are based on a two-step approach: the dynamical stage of the collision was described with the microscopic constrained molecular dynamics (CoMD) model, as well as the phenomenological deep-inelastic transfer (DIT) model and its modified (DITm) version. The deexcitation of the hot projectile fragments was performed with the statistical multifragmentation model (SMM) and the binary-decay model gemini, which provided nearly similar results for the neutron-rich products from the reactions studied. An overall good agreement of the calculations with the experimental results, especially for near-projectile isotopes was observed using both the CoMD model and the DITm model for the dynamical stage. The successful description of the production of neutron-rich isotopes with the CoMD model is of particular importance, due to the predictive power of the microscopic approach that essentially does not depend on the reaction dynamics. Our studies to date suggest that peripheral heavy-ion collisions at this energy range (i.e., well above the Coulomb barrier, but below the Fermi energy), if induced by neutron-rich rare-isotope beams of adequate intensity may offer a unique route to access extremely neutron-rich rare isotopes toward the astrophysical $r$-process path and the presently uncharted neutron drip line.

Approaching neutron-rich nuclei toward ther-process path in peripheral heavy-ion collisions at 15 MeV/nucleon

The production cross sections of projectilelike fragments from the interaction of 15 MeV/nucleon ${}^{86}$Kr with ${}^{64}$Ni and ${}^{58}$Ni and with ${}^{124}$Sn and ${}^{112}$Sn were measured using a magnetic separator with emphasis on the neutron-rich isotopes. Neutron pickup isotopes (with up to six neutrons picked up from the target) were observed with large cross sections. Calculations involving the the deep-inelastic transfer model as well as the microscopic constrained molecular dynamics model (CoMD) for the primary interaction stage coupled to the statistical deexcitation code gemini were used to describe the gross properties of the product distributions. The present results were also compared with our previous data of the same reactions at 25 MeV/nucleon. The data at 15 MeV/nucleon show enhanced production of neutron-rich isotopes very close to the projectile, relative to the corresponding data at 25 MeV/nucleon. This enhancement in the cross sections is possibly associated with very peripheral collisions and longer interaction times of the neutron-rich ${}^{86}$Kr projectile with the neutron-rich targets. The large cross sections of such reactions well above the Coulomb barrier, but below the Fermi energy, involving peripheral nucleon exchange, suggest that both the $N\text{/}Z$ of the projectile and the $N\text{/}Z$ of the target may properly be exploited in the production of neutron-rich rare isotopes. These reactions offer a novel and attractive route to access extremely neutron-rich rare isotopes toward the the astrophysical $r$-process path and, possibly, the neutron drip-line.

Neutron-rich rare isotope production in the Fermi energy domain and application to the Texas A&M radioactive beam upgrade

The production and separation of neutron-rich rare isotope beams in peripheral collisions around the Fermi energy is described in the present work. The experiments were performed at the Cyclotron Institute of Texas A&M University employing beams from the K500 Superconducting Cyclotron. Two magnetic separators were used: the MARS recoil separator and the Superconducting Solenoid Line (BigSol Line). Enhanced production cross sections of neutron-rich nuclides in comparison with high-energy fragmentation mechanisms were observed and attributed to the role of the N/Z and the nuclear periphery of the target. From a practical viewpoint, these reactions below or around the Fermi energy offer a promising way to access very neutron-rich rare isotopes. The experience obtained in the production of rare isotope beams (RIB) in this energy range will be applied in the ongoing RIB upgrade of the Cyclotron Institute that will involve production, stopping and re-acceleration of rare isotopes.

Neutron-rich rare isotope production below the Fermi energy and its application to the Texas A&M RIB upgrade

Recent efforts to produce and separate neutron-rich rare isotopes in peripheral collisions below the Fermi energy are presented. The experiments have been performed at the Cyclotron Institute of Texas A&M University employing beams from the K500 Superconducting Cyclotron. Two magnetic separators were used: the MARS recoil separator and the Superconducting Solenoid Line (BigSol Line). An enhanced production of neutron-rich nuclides in comparison with high-energy fragmentation mechanisms has been observed and attributed to the role of the N/Z and the nuclear periphery of the target. From a practical viewpoint, these reactions below or around the Fermi energy offer a novel way to access very neutron-rich rare isotopes. The experience obtained in the production of rare isotope beams (RIB) below the Fermi energy will be exploited in the ongoing RIB upgrade of the Cyclotron Institute that will involve production, stopping and reacceleration of rare isotopes.

Neutron-rich rare isotope production and studies of the N/Z degree of freedom in binary collisions at Fermi energies

The production of neutron-rich projectile residues in deep-inelastic collisions at Fermi energies and the scaling of their yields are investigated in this work. A large enhancement in the production of neutron-rich fragments was observed in the reactions of a 25 MeV/nucleon 86Kr beam with the neutron rich 64Ni and 124Sn targets. Simulations using a deep-inelastic transfer (DIT) code indicate that the neutron skins of the neutron-rich targets play an important role. From a practical viewpoint, such reactions may offer a novel way to access very neutron-rich rare isotopes. In parallel to the production studies, the scaling properties of the residue yields are investigated. An approach to study the process of N/Z equilibration has been developed based on residue yield ratios. This approach may provide a valuable tool of isospin studies with radioactive beams.

Neutron-rich rare isotope production in the Fermi energy domain

The production of neutron-rich rare isotopes around the Fermi energy is investigated in the present work. A large enhancement in the production of neutron-rich projectile residues has been observed in the reactions of a 25 MeV/nucleon 86 Kr beam with the neutron rich 64 Ni and 124 Sn targets relative to the predictions of the EPAX parametrization of high-energy fragmentation, as well as relative to the reaction with the less neutron-rich 112 Sn target. The present data demonstrate the significant influence of the target neutron-to-proton ratio (N/Z) in peripheral collisions at Fermi energies. A hybrid model based on a deep-inelastic transfer code (DIT) followed by a statistical de-excitation code was found to account for part of the observed large cross sections. The DIT simulation indicates that the neutron skins of the neutron-rich 64 Ni and 124 Sn target nuclei play an important role in the production mechanism. From a practical viewpoint, such reactions between massive neutron-rich nuclei offer a novel synthetic avenue to access extremely neutron-rich rare isotopes towards the neutron-drip line.

Neutron-rich rare isotope production in the Fermi energy domain

The production of neutron-rich rare isotopes around the Fermi energy is investigated in the present work. A large enhancement in the production of neutron-rich projectile residues has been observed in the reactions of a 25 MeV/nucleon 86Kr beam with the neutron rich 64Ni and 124Sn targets relative to the predictions of the EPAX parametrization of high-energy fragmentation, as well as relative to the reaction with the less neutron-rich 112Sn target. The present data demonstrate the significant influence of the target neutron-to-proton ratio (N/Z) in peripheral collisions at Fermi energies. A hybrid model based on a deep-inelastic transfer code (DIT) followed by a statistical de-excitation code was found to account for part of the observed large cross sections. The DIT simulation indicates that the neutron skins of the neutron-rich 64Ni and 124Sn target nuclei play an important role in the production mechanism. From a practical viewpoint, such reactions between massive neutron-rich nuclei offer a novel synthetic avenue to access extremely neutron-rich rare isotopes towards the neutron-drip line.

Enhanced production of neutron-rich rare isotopes in peripheral collisions at Fermi energies.

A large enhancement in the production of neutron-rich projectile residues is observed in the reactions of a 25 MeV/nucleon 86Kr beam with the neutron-rich 124Sn and 64Ni targets relative to the predictions of the EPAX parametrization of high-energy fragmentation, as well as relative to the reaction with the less neutron-rich 112Sn target. A hybrid model based on a deep-inelastic transfer (DIT) code followed by a statistical deexcitation code accounts for part of the observed large cross sections. The DIT simulation indicates that the production of neutron-rich nuclides in these reactions is associated with peripheral nucleon exchange in which the neutron skins of the neutron-rich 124Sn and 64Ni target nuclei may play an important role. From a practical viewpoint, such reactions offer a novel synthetic avenue to access extremely neutron-rich rare isotopes towards the neutron-drip line.

Enhanced production of neutron-rich rare isotopes in the reaction of 25 MeV/nucleon 86Kr on 64Ni

The cross sections and velocity distributions of projectile-like fragments from the reaction of 25 MeV/nucleon 86Kr+64Ni have been measured using the MARS recoil separator at Texas A&M, with special emphasis on the neutron rich isotopes. Proton-removal and neutron pick-up isotopes have been observed with large cross sections. A model of deep-inelastic transfer (DIT) for the primary interaction stage and the statistical evaporation code GEMINI for the deexcitation stage have been used to describe the properties of the product distributions. The results have also been compared with the EPAX parametrization of high-energy fragmentation yields. The experimental data show an enhancement in the production of neutron-rich isotopes close to the projectile, relative to the predictions of DIT/GEMINI and the expectations of the high-energy cross section parametrization EPAX. This enhancement is associated with peripheral interactions of the neutron rich 86Kr projectile with the neutron rich 64Ni target. The large cross sections of such reactions near the Fermi energy, involving peripheral nucleon exchange, suggest that both the N/Z of the projectile and the N/Z of the target may properly be exploited in the production of neutron-rich rare isotopes. This synthesis approach at this energy regime may offer a fruitful pathway to extremely neutron-rich nuclei, towards the neutron-drip line.