Projectile-like Fragments Research Articles

Projectile fragments from peripheral collisions of 25 MeV/nucleon 64Ni on 64Ni

We study the yields and the momentum distributions of projectile-like fragments from peripheral collisions of 64Ni (25 MeV/nucleon) on 64Ni. The experimental data were obtained in previous works with the BigSol separator system at the Cyclotron Institute of Texas A&M University. Projectile fragments were collected and analyzed at forward angles (1.5°-3.0°). The production cross sections and the momentum distributions (p/A) of the fragments were systematically studied and compared with the Deep-Inelastic Transfer (DIT) model and the Constrained Molecular Dynamics (CoMD) model followed by the deexcitation model GEMINI. Special attention is given to the possibility to produce neutron-rich rare isotopes of elements at the beginning of the astrophysical r-process. Moreover, efforts to reconstuct the excitation energy distributions are ongoing in hopes to shed light to the reaction mechanisms of peripheral collisions at this energy (25 MeV/nucleon).

Probing Cluster Transfer in Peripheral Collisions of 40Ar on 64Ni at 15 MeV/nucleon

This work focuses on the study of the yields and momentum distributions of projectile-like fragments from 40Ar collisions with target 64Ni at 15 MeV/nucleon, using experimental data obtained in previous work with the MARS spectrometer at the Cyclotron Institute at Texas A&M University. Motivated by the current activity on clustering, we focused our attention on the channel corresponding to the production of the 36S ejectile, which may have resulted from the removal of an alpha particle cluster from the 40Ar projectile. The experimental distributions were compared with two dynamical models, the deep-inelastic transfer (DIT) model and the constrained molecular dynamics (CoMD) model, followed by the de-excitation code GEMINI. The observed discrepancies potentially indicate direct cluster transfer in quasi-elastic peripheral collisions. By comparing our experimental data with appropriate models, we hope to gain valuable insight into the mechanisms governing clustering and cluster transfer in peripheral collisions in the Fermi energy regime.

Multinucleon Transfer in 25 MeV/nucleon 86Kr + 64Ni, 124Sn Peripheral Collisions

In this work we investigate multinucleon transfer reaction channels in peripheral collisions between a 86Kr projectile at 25 MeV/nucleon with 64Ni and 124Sn targets. The experimental data of these reactions were obtained with the Momentum Achromat Recoil Separator (MARS) at Texas A&M University in previous works of our group. We extracted and compared experimental mass and momentum per nucleon distributions of ejectiles with a two step model calculation. For the interaction of the projectile with the target, the phenomenological Deep Inelastic Transfer model (DIT) and the microscopic Constrained Molecular Dynamics model (CoMD) were used, both followed by the GEMINI model for the de-excitation of the primary excited projectile-like fragments. Generally, both DIT and CoMD appear to describe the trend of the data for both systems. However, possible further improvements in the models may be necessary. In conjunction with our recent work with a 86Kr beam at 15 MeV/nucleon with a 64Ni target, this study provides further insights into the reaction mechanisms of peripheral collisions in the Fermi energy regime and the production of neutron rich nuclides.

Validation of nuclear physics models for the fragmentation of 16O ＋ Al at beam energies from 290[formula omitted] to 1000[formula omitted] MeV

We have validated the predictions of SAPTON, and Geant4 models QGSP-INCLXX, and SHIELDING, with the experimental charge cross-sections of 16O ＋ Al reaction at beam energies ranging from 290 MeV/u to 1000 MeV/u. SAPTON exhibits reasonable agreement with the data compared to Geant4 models. While Geant4 favors the intra-nuclear cascade process to produce particles with charge Z ≤ 2, in abundance, SAPTON favors the breakup into projectile-like and target-like fragments, and hence shows better agreement with the data.

Velocity and Isotope Distributions of Projectile-Like Fragments in Reaction $${}^{40}$$Ar (36.5 A MeV)/$${}^{9}$$Be

Velocity and Isotope Distributions of Projectile-Like Fragments in Reaction $${}^{40}$$Ar (36.5 A MeV)/$${}^{9}$$Be

Momentum Distribution Studies of Projectile Fragments from Peripheral Collisions Below the Fermi Energy

This paper presents our recent studies of multinucleon transfer in peripheral collisions in reactions below the Fermi regime. Our current focus is the study of the mass, angular and momentum distributions of the projectile-like fragments from the reaction of an 86Kr beam at 15 MeV/nucleon with a target of 64Ni. Experimental data from our previous work with the MARS spectrometer at the Cyclotron Institute of Texas A&M University were compared with model calculations. The dynamical stage of the reaction is described with either the Deep-Inelastic Transfer Model (DIT) or with the microscopic Constrained Molecular Dynamics model (CoMD). The de-excitation of the hot projectile-like fragments is performed with the GEMINI model. The momentum distributions are characterized by a quasi-elastic peak and a deep-inelastic peak. Two-body kinematics was employed to extract the total excitation energies of these regions. Through the thorough study of peripheral reactions in the Fermi energy regime we expect to gain valuable information that could lead to the understanding of how the rare isotopes in regions such as the r-process path and the neutron drip line are formed and the reaction mechanism(s) that take place.

Contributions of quasifission and fusion-fission in the Mg24 + Hf178 reaction at 145 MeV laboratory beam energy using the Boltzmann-Uehling-Uhlenbeck model

Background: Understanding the mechanism of the quasifission reaction is important, because it is an essential competitor to the fusion reaction leading to superheavy elements. However, it is a challenge to separate the quasifission and fusion-fission components.Purpose: This paper provides a dynamics description of the $^{24}\mathrm{Mg}+^{178}\mathrm{Hf}$ reaction at laboratory beam energy of 145 MeV, and studies contributions of quasifission and fusion-fission in the reaction.Method: The Boltzmann-Uehling-Uhlenbeck model is improved to study the heavy-ion collision at incident energy near the Coulomb barrier. A method is developed to determine the window of the dinuclear system during the evolution.Results: It is shown that the fusion occurs with a large percentage in the central collision, and the quasiinelastic scattering occurs mainly in the peripheral collision. The quasifission competes with the fusion in collisions with small impact parameters. It is found that the cross sections of quasifission decrease and those of fusion increase with increasing surface energy or incompressibility. The mass-angular correlation of the quasifission events shows the mass asymmetry. The fragments emitted at the front angle are targetlike fragments and those at the back angle are projectilelike fragments. Furthermore, the differential cross sections at the angles ${0}^{\ensuremath{\circ}}$ and ${180}^{\ensuremath{\circ}}$ are larger than that at ${90}^{\ensuremath{\circ}}$.Conclusions: By comparing the calculations of the mass distribution and mass-angular correlation to the data, it is deduced that the compound nucleus fission plays a main role and accounts for the characteristic of fragment observables in the $^{24}\mathrm{Mg}+^{178}\mathrm{Hf}$ reaction at laboratory beam energy of 145 MeV.

Investigating the time dependence of neutron-proton equilibration using molecular dynamics simulations

Neutron-proton equilibration has previously been studied experimentally in dynamically deformed nuclei in heavy ion collisions [Phys. Rev. Lett. 118, 062501 (2017); Phys. Rev. C 95, 044604 (2017)] using the NIMROD detector array at the Cyclotron Institute at Texas A University. Results indicated the composition of the two heaviest fragments originating from the excited projectile-like fragment evolved exponential with respect to their orientation angle to be more similar. Constrained Molecular Dynamics and Antisymmetrized Molecular Dynamics simulations were performed for different formulations of the density dependence of the asymmetry energy term of the nuclear equation of state. The simulations are compared to experimental results, which indicate a better agreement with a softer interaction in the nuclear equation of state.

Characteristic time scale of cluster production at the Fermi energy

The study of heavy-ion collisions in the Fermi energy domain (20 MeV/nucleon < E/A < 100 MeV/nucleon) is a fundamental research topic in modern nuclear physics. In the case of semi-peripheral collisions, the Fermi energy regime is characterized by the formation of a transient, neck-like structure that connects a projectile-like fragment (PLF) with a target-like fragment (TLF). The neck structure represents a precursor of the fireball which is a typical overlap of participating nucleons at relativistic energies (E/A> 200 MeV/nucleon). It undergoes an expansion phase in a short time scale of the order of 100 fm/c with the formation of a low-density region of nuclear matter, therefore favoring the clusterization of intermediate mass fragments (IMFs) of atomic number Z (typically) less than 20. Particular emphasis is given to some relevant results obtained by the CHIMERA collaboration in the last decade, regarding the time scale of the production mechanisms of the intermediate mass fragments in neck fragmentation and their neutron enrichment.

Study of Multinucleon Transfer Mechanisms in 86Kr-Induced Peripheral Reactions at 15 and 25 MeV/nucleon

This paper presents our recent studies of the multinucleon transfer in peripheral collisions in reactions near the Fermi regime. Specifically, the reactions of a 86Kr beam at 15 MeV/nucleon with targets of 124Sn ,112Sn, 64Ni and 58Ni and reactions of a 86Kr beam at 25 MeV/nucleon with targets of 124Sn and 112Sn. The experimental data were obtained from the previous work of our group with the MARS spectrometer at the Cyclotron Institute of Texas A&M University. Our current focus is the thorough study of the experimental mass and momentum distributions of the projectile-like fragments. The momentum distributions are characterised by a narrow quasi-elastic peak and a broader deep-inelastic peak. We employed two-body kinematics to characterize the excitation energies of these reactions. We also compared the data with model calculations. The dynamical stage is described with either the Deep-Inelastic Transfer Model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The de-excitation of the hot projectile-like fragments is performed with the Gemini model. Studying these reactions will provide us with a better understanding as to how the energy of the beam and the different targets affect the mechanism of the multinucleon transfer reactions. With the recent work, our continued efforts in the study of peripheral reactions in the Fermi energy regime delineate new opportunities to elucidate the reaction mechanism(s) of rare isotope production and may effectively contribute to the study of unexplored regions of the nuclear chart toward the r-process and the neutron drip line.

Determination of Co57(n,xp ) cross sections using the surrogate reaction ratio method

The compound nuclei $^{58}\mathrm{Co}^{*}$ and $^{61}\mathrm{Ni}^{*}$ have been populated at overlapping excitation energies by transfer reactions $^{56}\mathrm{Fe}(^{6}\mathrm{Li},\ensuremath{\alpha})^{58}\mathrm{Co}^{*}$ (surrogate of $n+^{57}\mathrm{Co}$) at ${E}_{\mathrm{lab}}$ = 35.9 MeV and $^{59}\mathrm{Co}(^{6}\mathrm{Li},\ensuremath{\alpha})^{61}\mathrm{Ni}^{*}$ (surrogate of $n+^{60}\mathrm{Ni}$) at ${E}_{\mathrm{lab}}$ = 40.5 MeV, respectively. The $^{57}\mathrm{Co}(n,xp$) cross sections in the equivalent neutron energy range of 8.6--18.8 MeV have been determined within the framework of surrogate reaction ratio method using $^{60}\mathrm{Ni}(n,xp$) cross section values from the literature as reference. The proton decay probabilities of the compound systems have been determined by measuring evaporated protons at backward angles in coincidence with projectile-like fragments detected around the grazing angle. The measured $^{57}\mathrm{Co}(n,xp$) cross sections are in good agreement with both the predictions of talys-1.8 statistical model code with default parameters using different microscopic level densities and data evaluation library jeff-3.3 up to equivalent neutron energy $\ensuremath{\approx}12.6$ MeV, while for higher energies the measured $^{57}\mathrm{Co}(n,xp$) cross sections are found to be consistently higher than the predictions. However, the talys-1.8 calculations with modified values of input potential parameters provide a reasonable reproduction of the measured $^{57}\mathrm{Co}(n,xp$) cross sections for the entire neutron energy range. The observed discrepancies at higher energies between the experimental data and the predictions of both the jeff-3.3 library and the talys-1.8 calculations with default parameters indicate the need of new evaluations for this reaction.

Experimental study of the Ca40,48+Ca40,48 reactions at 35 MeV/nucleon

In this article we investigate $^{40,48}$Ca+$^{40,48}$Ca peripheral and semi-peripheral reactions at 35 MeV/nucleon. Data were obtained using the unique coupling of the VAMOS high acceptance spectrometer and the INDRA charged particle multidetector.The spectrometer allowed high resolution measurement of charge, mass and velocity of the cold projectile-like fragment (PLF), while the INDRA detector recorded coincident charged particles with nearly $4\pi$ acceptance.The measured isotopic composition of the PLF identified in VAMOS and the average light charged particle (LCP) multiplicities are promising observables to study the isospin diffusion.The detection of the PLF in coincidence with LCP allows the reconstruction of the mass, charge and excitation energy of the associated initial quasi-projectile nuclei (QP), as well as the extraction of apparent temperatures.We investigate the suitability of the isoscaling method with the PLF and the experimental reconstructed QP.The extracted $\alpha$ and $\Delta$ isoscaling parameters present a dependence on the considered system combination that could justify their use as a surrogate for isospin asymmetry in isospin transport studies.The reconstruction of the QP allows to observe an evolution of the $\alpha/\Delta$ with the size of the QP, the latter being consistent with a strong surface contribution to the symmetry energy term in finite nuclei. This leads to the conclusion that the reconstruction of the primary source is mandatory for the study of the symmetry energy term based on the isoscaling method for such reactions.

Erratum: Kinetic energy spectra and angular distributions of projectile-like fragments in C12,13+Nb93 reactions [Phys. Rev. C 102 , 024610 (2020)

Received 21 June 2021DOI:https://doi.org/10.1103/PhysRevC.104.039901©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLow & intermediate energy heavy-ion reactionsTransfer reactionsNuclear Physics

Selection of the optimal condition for the production of light neutron-rich isotopes in multinucleon transfer reactions

Light neutron-rich isotopes are populated as products of the multinucleon transfer reaction following the collisions of $^{64}\mathrm{Ni}$ beams onto $^{130}\mathrm{Te}, ^{208}\mathrm{Pb}$, and $^{238}\mathrm{U}$ targets and $^{40}\mathrm{Ar}$ beams onto $^{197}\mathrm{Au}, ^{208}\mathrm{Pb}$, and $^{238}\mathrm{U}$ targets at bombarding energies slightly above the Coulomb barrier. Distribution characteristics of projectile-like fragments are studied in the framework of dinuclear system concept where dynamic deformation is taken into account. The odd-even effect in the diffusion process is discussed, and the distribution of final isotopes can be well reproduced by the effective local excitation energies excluding pairing energies. Compared with the experimental data, it is found that the heavier (i.e., larger $N/Z$ ratio) the target is, the more likely it is to produce light neutron-rich isotopes.

Role of neutron excess in the projectile for the production of heavy neutron-rich nuclei

To shed light on the conditions for synthesizing some new heavy neutron-rich nuclei using multinucleon transfer reactions, the reaction systems $^{40}\mathrm{Ca}+^{208}\mathrm{Pb}$, $^{58}\mathrm{Ni}+^{208}\mathrm{Pb}$, $^{40}\mathrm{Ar}+^{208}\mathrm{Pb}$, $^{64}\mathrm{Ni}+^{208}\mathrm{Pb}$, and $^{136}\mathrm{Xe}+^{208}\mathrm{Pb}$ are investigated within improved dinuclear system (DNS) $\mathrm{model}+$gemini$++$. The transfer cross sections are calculated and compared with existing experimental data. The calculated results are in good agreement with available data. One found the projectiles are changed from the neutron-deficient $^{40}\mathrm{Ca}$ and $^{58}\mathrm{Ni}$ to moderately neutron-rich $^{40}\mathrm{Ar}$, and neutron-rich $^{64}\mathrm{Ni}$ and $^{136}\mathrm{Xe}$ projectiles on $^{208}\mathrm{Pb}$ target, the transfer flux its trend gradually evolves from proton stripping and neutron pickup to the proton pickup and neutron stripping and pickup (pickup and stripping are referring to the projectilelike fragment).

Kinetic energy spectra and angular distributions of projectile-like fragments in C12,13+Nb93 reactions

Kinetic-energy spectra and angular distributions of the projectile-like fragments were measured in $^{12,13}\mathrm{C}+^{93}\mathrm{Nb}$ reactions at ${E}_{\mathrm{lab}}=65\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ to investigate the reaction mechanisms involving the role of projectile and target structures. It has been observed that one-nucleon pick-up reactions lead to the formation of target-like fragments predominantly in the ground state, whereas nucleon transfer to the target occurs predominantly in the excited states for both $^{12}\mathrm{C}+^{93}\mathrm{Nb}$ and $^{13}\mathrm{C}+^{93}\mathrm{Nb}$ reactions. In the case of $^{93}\mathrm{Nb}(^{12}\mathrm{C}, ^{15}\mathrm{N})^{90}\mathrm{Zr}$ reactions, a significant yield was observed for $^{15}\mathrm{N}$ (``$1p+2n$'' pick-up) indicating the role of the $N=50$ shell in $^{90}\mathrm{Zr}$. Observation of a systematic increase in the forward peaking of the angular distributions of projectile-like fragments with an increasing number of nucleon transfers indicates an increase in the projectile-target overlap with increasing mass transfer. Angular distributions for inelastic scattering as well as transfer channels populating various states of projectile-like fragments and/or target-like fragments were calculated simultaneously by using the coupled reaction channels code fresco and were in reasonable agreement with the experimental data. New (modified) spectroscopic amplitudes have been proposed for some of the unknown (known) overlapping states for calculating transfer cross sections. In the case of $^{13}\mathrm{C}+^{93}\mathrm{Nb}$, the transfer channels corresponding to ``$2n$'' and ``$1p+1n$'' pick-up channels were not observed. This may be due to the higher N/Z ratio of the projectile, highlighting the importance of projectile structure in addition to that of the target.

Multinucleon transfer dynamics in nearly symmetric nuclear reactions

Within the framework of the dinuclear system model, the multinucleon transfer dynamics for nearly symmetric nuclear collisions has been investigated. The reaction mechanism in the systems of $$^{198}\hbox {Pt}+^{198}\hbox {Pt}$$ and $$^{204}\hbox {Hg}+^{198}\hbox {Pt}$$ was investigated at beam energies around the Coulomb barrier. It was found that the isotopic yields are enhanced with increased incident energy in the domain of proton-rich nuclides. However, the production on the neutron-rich side weakly depends on the energy. The angular distribution with the beam energy was also analyzed in the multinucleon transfer reactions. Projectile-like fragments were produced toward the forward emission with increasing incident energy. The target-like fragments manifested the opposite trend in the transfer reactions.

Isoscaling and nuclear reaction dynamics

Isoscaling parameters $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ have been explored as a function of breakup angle in binary excited projectile-like fragment decays produced in collisions of $^{70}\mathrm{Zn}+^{70}\mathrm{Zn}$ and $^{64}\mathrm{Zn}+^{64}\mathrm{Zn}$ at 35 MeV per nucleon. In this analysis, focus was placed on isoscaling the second heaviest fragment with $4\phantom{\rule{0.16em}{0ex}}\ensuremath{\le}\phantom{\rule{0.16em}{0ex}}{Z}_{L}\phantom{\rule{0.16em}{0ex}}\ensuremath{\le}\phantom{\rule{0.16em}{0ex}}8$ emitted from the excited projectile-like fragment in events that contained a heavy fragment with ${Z}_{H}\phantom{\rule{0.16em}{0ex}}\ensuremath{\ge}\phantom{\rule{0.16em}{0ex}}12$. The breakup orientation ${\ensuremath{\theta}}_{\mathrm{prox}}$ was defined as the angle between the heavy and light fragments' center-of-mass velocity and the fragment pairs' relative velocity. Breakups between ${0}^{\ensuremath{\circ}}<{\ensuremath{\theta}}_{\mathrm{prox}}\ensuremath{\le}{80}^{\ensuremath{\circ}}$ have been shown to be dominated by dynamical contributions, while break-up angles of ${\ensuremath{\theta}}_{\mathrm{prox}}>{100}^{\ensuremath{\circ}}$ are predominantly statistical. Historically, isoscaling has often been understood and applied in a statistical context, assuming that the fragments are produced after statistical equilibrium is achieved. Studying isoscaling parameters as a function of ${\ensuremath{\theta}}_{\mathrm{prox}}$ reveals the sensitivity of $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ to the mechanism of fragment production.

Approaching the neutron-rich heavy and superheavy nuclei by multinucleon transfer reactions with radioactive isotopes

The dynamical mechanism of multinucleon transfer (MNT) reactions has been investigated within the dinuclear system (DNS) model, in which the sequential nucleon transfer is described by solving a set of microscopically derived master equations. Production cross sections, total kinetic energy spectra, angular distribution of formed fragments in the reactions of $^{124,132}$Sn+ $^{238}$U/$^{248}$Cm near Coulomb barrier energies are thoroughly analyzed. It is found that the total kinetic energies of primary fragments are dissipated from the relative motion energy and rotational energy of the two colliding nuclei. The fragments are formed in the forward angle domain. The energy dependence of the angular spectra is different between projectile-like and target-like fragments. Isospin equilibrium is governed under the potential energy surface. The production cross sections of neutron-rich isotopes are enhanced around the shell closure.

Heavy Ion Nuclear Reaction Impact on SEE Testing: From Standard to Ultra-high Energies

We perform Monte Carlo (MC) simulations to describe heavy ion (HI) nuclear interactions in a broad energy range (4 MeV/n-150 GeV/n), focusing on the single event effect (SEE) sub-linear energy transfer (LET) impact. Previously retrieved single event latch-up (SEL) experimental data have indicated that standard energy ions (~10 MeV/n) can produce high-LET secondaries through fusion reactions which are expected to strongly influence the SEE cross section in the sub-LET region. Alternatively, interactions of higher energy ions (>100 MeV/n) yield secondaries of a similar LET distribution as from the projectile, for projectile-like fragments, and high-energy proton reactions, for target-like fragments. Hence, the factor of relevance to the sub-LET SEE cross section is correlated to low-energy.