Deep Inelastic Collisions Research Articles

Insights from multinucleon transfer reactions in 206Pb+118Sn

Multinucleon transfer reactions for the 206Pb +118 Sn system were measured at Elab = 1200 MeV using the PRISMA large solid-angle magnetic spectrometer. The experiment was conducted at laboratory angles around the grazing angle, covering an angular range of approximately 20°. The resulting differential and total cross sections, along with Q-value distributions for various neutron and proton pick-up and stripping channels, are presented. The Q-value distributions suggest a transition from quasi-elastic to deep inelastic collision processes, particularly in channels involving nucleon transfers. The experimental results have been compared with GRAZING code calculations, showing good agreement for few-nucleon transfer channels, while channels with large nucleon transfers are underestimated, indicating the involvement of more complex processes.

Kinematic fitting of neutral current events in deep inelastic ep collisions.

In this paper we present a technique to reconstruct the scaling variables defining ep deep inelastic scattering by performing a kinematic fit. This reconstruction technique makes use of the full potential of the data collected. It is based on Bayes' Theorem and involves the use of informative priors. The kinematic fit method has been tested using a simulated sample of ep neutral current events at a center of mass energy of 318 GeV with Q 2 > 400 GeV2. In addition to the scaling variables, this method is able to estimate the energy of possible initial state radiation (Eγ ) which otherwise goes undetected. A better resolution than standard electron and double angle techniques in the reconstruction of scaling variables is achieved using a kinematic fit.

STRUCTURAL YIELDS AND ASPECTS OF ISOMER IN DEEP-INELASTIC COLLISIONS

Structural yields and features in the meta-stable states of nuclei from the projectile like fragments of 8.36 MeV 76Ge in 198Pt target are reported. The dynamic features of deep inelastic collisions (DICs) are studied by dissipation energy versus transfer of nucleons. We have studied the yields as a function of excitation levels. The structural appears do not depend on the excitation energy of isomers persuaded in the DICs. This is in dissimilarity to the protuberant physical landscapes establishing in population yield of isotopes which disappear with Gaussian distribution.

Mass Equilibration and Fluctuations in the Angular Momentum Dependent Dynamics of Heavy Element Synthesis Reactions.

Mass and angle distributions for the ^{52}Cr+^{198}Pt and ^{54}Cr+^{196}Pt reactions (both forming ^{250}No) were measured and subtracted, giving new information on fast quasifission mass evolution, and the first direct determination of the dependence of sticking times on angular momentum. TDHF calculations showed good agreement with average experimental values, but experimental mass distributions unexpectedly extended to symmetric splits while the peak yield remained close to the initial masses. This implies a strong role of fluctuations in mass division early in the collision, giving insights into the transition from fast energy dissipative deep-inelastic collisions to quasifission.

Production mechanism of the neutron-rich nuclei in multinucleon transfer reactions: A reaction time scale analysis in energy dissipation process

The energy dissipation processes in multinucleon transfer reactions of 136Xe+198Pt at incident energies Elab=5.59 and 7.98 MeV/nucleon are investigated by using the improved quantum molecular dynamics model. The total-kinetic-energy-mass (TKE-Mass) distributions, the total kinetic energy loss (TKEL) distributions, and the excitation energy distributions of the primary binary products under different contact time scales of the reaction partners are analyzed. It shows that the value of the energy dissipation has an increasing trend over contact time. The quasielastic, the deep-inelastic, and the quasifission events can be roughly distinguished by the contact time. By analysing the correlation between the isotopic cross sections and the contact time, we find that the neutron-rich nuclei are produced in the deep-inelastic collisions.

Theoretical progress on production of isotopes in the multinucleon transfer process

As one promising approach for producing nuclei beyond the [Formula: see text]-stability line, the multinucleon transfer (MNT) process has been extensively investigated in past decades. An overview of the theoretical progress on production of isotopes in MNT process is presented. The dinuclear system model, one hybrid approach (GRAZING+DNS model), the improved quantum molecule dynamic model, and the model based on the Langevin equations are summarized. The nucleon transfer mechanisms, such as effects of quasi-elastic and deep inelastic collisions, energy dissipation, [Formula: see text] equilibration, and shell structure in collisions of two complex nuclei are discussed. We present the progress on production of the exotic nuclei near the neutron-drip line, the neutron-rich isotopes near [Formula: see text], and the transuranium nuclei.

Fragmentation analysis of 105Ag∗ nucleus governed via complete and incomplete fusion channels at Ec.m. = 89MeV

A systematic study of dynamical aspects associated with heavy-ion-induced [Formula: see text] reaction is carried out at center-of-mass energy [Formula: see text] MeV. The complete fusion (CF) and incomplete fusion (ICF) contributions are estimated by using the dynamical cluster-decay model (DCM). The incomplete fusion component is examined by normalizing the incident beam energy for each of the breakup fragment. The fusion evaporation cross-sections that emerged from CF and ICF channels are duly addressed using the optimized value of neck-length parameter [Formula: see text]. Further, the mass yield of compound nuclei (CN) formed in the CF and ICF processes is analyzed with respect to angular momentum [Formula: see text] values. The DCM-based calculations indicate the possible contribution of deep inelastic collision (DIC) in the decay of [Formula: see text] at higher [Formula: see text] values, and DIC cross-sections are predicted which call for future validation.

Angular momentum as a probe for the reaction mechanism: The [formula omitted] decay at three excitation energies

The angular momentum effects on the reaction mechanism in the decay of a hot system, formed in 48Ti + 40Ca → Mo⁎88 reaction at three excitation energies, have been studied using the dynamical cluster-decay model based on the quantum mechanical fragmentation theory. Angular momentum windows have been defined for the compound and non-compound nucleus processes (like deep inelastic collisions etc.) with respect to the angular momentum variation of the fission barriers of the incoming channel. First, the angular momentum distributions of the summed up preformation, penetration probabilities and the cross-sections for light particles, intermediate mass fragments and fission fragments have been calculated by considering the angular momentum up to the critical value. Then, the mass and charge distributions (with isotopic compositions) of the cross-sections have been calculated in accordance with the defined angular momentum windows. The cross-sections for fragments coming both from the compound nucleus decay and from other processes have been calculated and the total reaction cross-section is compared with the one presented in the work of Valdré and co-workers. The ratios of the observed fusion-evaporation and total fusion cross-sections to the total reaction cross-sections of (i) our calculation and (ii) presented in the work of Valdré and co-workers, are compared and found comparable. The change of the reaction mechanism has been analyzed as a function of the angular momentum variation of the cross-sections of the fission fragments. Finally, the effect of the incident energy on the compound nucleus formation and survival probabilities has been studied.

Fragmentation analysis of 88Mo* compound nucleus in view of different decay mechanisms

In reference to the experimental data, the decay mechanism of 88Mo* compound system formed in 48Ti+40Ca reaction is investigated at three beam energies (Ebeam = 300, 450, and 600 MeV) using the collective clusterization approach of Dynamical Cluster decay Model (DCM). The calculations are done for spherical choice of fragmentation and with the inclusion of quadrupole (β2) deformations having “optimum” orientations. According to the experimental evidence 88Mo* decays via Fusion-Evaporation (FE) and Fusion-Fission (FF) processes, thus the decay cross-sections of this hot and rotating compound system are calculated for both channels. In FF decay mode, the explicit contribution of Intermediate Mass Fragments (IMF), Heavy Mass Fragments (HMF) and fission fragments (symmetric/asymmetric) is detected within DCM framework. The calculated FE and FF decay cross-sections find nice agreement with the available experimental data. Experimentally, it has been observed that the total contribution of FE and FF decay cross-sections is less than the total reaction cross-sections possibly due to the presence of some nCN component such as deep inelastic collisions (DIC), which generally contributes above critical angular momentum (ℓcr). The possibility of DIC contribution can be addressed as a future assignment in view of diminishing pocket of interaction potential above ℓcr.

Probing the Nuclear Equation of State with Peripheral Heavy Ion Collisions at Fermi Energies

A systematic study of quasi-elastic and deep-inelastic collisions at Fermi energies is presented with the aim of obtaining insight into the underlying dynamics and the nuclear equation of state (EOS). Comparisons of experimental heavy-residue data to detailed calculations using the semiclassical microscopic model CoMD (Constrained Molecular Dynamics) are shown. The CoMD code implements an effective interac- tion with a nuclear-matter compressibility of K=200 (soft EOS) or K=380 (stiff EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential and imposes a constraint in the phase space occupation for each nucleon, restoring the Pauli principle during the collision. Preliminary results from these comparisons point to a soft equation of state (K=200) with a rather stiff density dependence of the isovector part (symmetry energy).

Analysis of multinucleon transfer reactions with spherical and statically deformed nuclei using a Langevin-type approach

An increasing interest in multinucleon transfer processes in low-energy deep inelastic (damped) collisions of heavy ions appeared in recent years is due, in part, to by the possibility of using them as a method of production of heavy neutron-enriched nuclei. Possible promising projectile-target combinations include nuclei deformed in the ground state (e.g., actinides). Mutual orientations of such the nuclei in the entrance channel of the reaction may significantly influence the reaction dynamics. Available experimental data on multinucleon transfer reactions with statically deformed as well as spherical heavy nuclei 144Sm + 144Sm, 154Sm + 154Sm, 160Gd + 186W, and 208Pb + 208Pb/238U have been analyzed within the developed model. A good agreement of the calculated quantities with the corresponding experimental data is reached. Special attention in the paper is paid to analysis of production possibility of the neutron-enriched isotopes of heavy and superheavy elements in multinucleon transfer processes in the 238U + 238U/248Cm/254Es collisions.

Intermediate Mass Fragments production at low energy: reaction mechanism and isospin influence

In this work, we present a recent study concerning the break-up of the Projectile-Like (PLF) into two fragments, following more violent deep-inelastic collisions in the reactions 78Kr + 40Ca and 86Kr + 48Ca at 10 A MeV, realized at INFN-Laboratori Nazionali del Sud by using the 4π multi detector CHIMERA. For these systems, we have already analyzed the fusion-evaporation and fission-like processes. A selection method has been developed, in order to discriminate PLF break up events from those due to other mechanisms which populate the same region of the phase- space. A preference for PLF aligned break-up, along the direction of the PLF-TLF separation axis with the light fragment emitted in the backward part, has been put in light, suggesting the presence of dynamical effects. Also a comparison between the neutron-rich 86Kr + 48Ca and neutron-poor 78Kr + 40Ca systems is presented, to put in evidence the isospin role in these processes.

Study of non-fusion products in the [formula omitted] reaction

The isotopic distribution of nuclei produced in the 50Ti + 249Cf reaction has been studied at the gas-filled recoil separator TASCA at GSI Darmstadt, which separates ions according to differences in magnetic rigidity. The bombardment was performed at an energy around the Bass barrier and with the TASCA magnetic fields set for collecting fusion-evaporation reaction products. Fifty-three isotopes located “north-east” of 208Pb were identified as recoiling products formed in non-fusion channels of the reaction. These recoils were implanted with energies in two distinct ranges; besides one with higher energy, a significant low-energy contribution was identified. The latter observation was not expected to occur according to kinematics of the known types of reactions, namely quasi-elastic, multi-nucleon transfer, deep-inelastic collisions or quasifission. The present observations are discussed within the framework of two-body kinematics passing through the formation of a composite system.

Incomplete mass transfer processes in 28Si +93Nb reaction

Cross sections of reaction products were measured in [Formula: see text]Si[Formula: see text]Nb reaction using recoil catcher technique involving by off-line gamma-ray spectrometry at beam energies of 105 and 155[Formula: see text]MeV. At [Formula: see text][Formula: see text]MeV, the contribution from different incomplete mass transfer processes is investigated. Results of the present studies show the contribution from deep inelastic collision (DIC), massive transfer or incomplete fusion (ICF) and quasi-elastic transfer (QET). The contribution from massive transfer reactions was confirmed from the fractional yield of the reaction products in the forward catcher foil. The present results are different from those from the reactions with comparatively higher entrance channel mass asymmetry with lighter projectiles, for which dominant transfer processes are ICF and QET which involve mass transfer predominantly from projectile to target. The [Formula: see text] values of the products close to the target mass were observed to be in a wide range, starting from [Formula: see text] of the target ([Formula: see text]Nb) and extending slightly below the [Formula: see text] of the composite system, consistent with the contribution from DIC and QET reactions. At [Formula: see text][Formula: see text]MeV, a small contribution from QET was observed in addition to complete fusion.

Dynamics of 47V* formed in 20Ne + 27Al reaction in view of fusion-fission and DIC mechanism

The decay mechanism of 47V* formed in direct kinematics (20Ne + 27Al is investigated within the collective clusterization approach of dynamical cluster decay model (DCM). All calculations are done for quadrupole (β 2i -deformed) choice of fragments by taking optimum orientations over a wide range of center of mass energies (E c. m. ∼ 83–125 MeV). According to the experimental evidence, there is a strong competition between fusion fission (FF) and deep inelastic collision (DIC) in the decay of 47V*, which are recognized as compound nucleus process and non-compound nucleus process, respectively. The decay cross sections of 47V* for both FF and DIC decay modes are addressed using DCM, and are found to be in agreement with the experimental data. It is important to mention that emitting fragments in both these decay channels maintain their homogeneity in terms of charge number, that lies in the region 3 ≤ Z ≤ 9. Hence, all possible isotopes contributing towards 3 ≤ Z ≤ 9 are taken into consideration here. Calculations of both FF and DIC are segregated on the basis of angular momentum windows, where 0 ≤ l ≤ l cr has been taken for FF and l cr < l ≤ l gr for DIC, as the later operates only due to the partial waves near grazing angular momentum. In DIC, preformation probability (P 0) is divided equally amongst the most favoured outgoing fragments. Moreover, the behavior of fragmentation potential, preformation probability, penetrability and emission time etc. is examined, in order to identify the most favorable isotopes contributing towards FF and DIC.

Production mechanism of new neutron-rich heavy nuclei in the [formula omitted] reaction

The multinucleon transfer reaction of Xe136+198Pt at Elab=7.98 MeV/nucleon is investigated by using the improved quantum molecular dynamics model. The quasielastic, deep-inelastic, and quasifission collision mechanisms are studied via analyzing the angular distributions of fragments and the energy dissipation processes during the collisions. The measured isotope production cross sections of projectile-like fragments are reasonably well reproduced by the calculation of the ImQMD model together with the GEMINI code. The isotope production cross sections for the target-like fragments and double differential cross sections of 199Pt, 203Pt, and 208Pt are calculated. It is shown that about 50 new neutron-rich heavy nuclei can be produced via deep-inelastic collision mechanism, where the production cross sections are from 10−3 to 10−6 mb. The corresponding emission angle and the kinetic energy for these new neutron-rich nuclei locate at 40∘–60∘ and 100–200 MeV, respectively.

Study of deep inelastic collisions within multidimensional dynamical model

Energy, angle, and charge distributions of binary products of the deep inelastic collisions of heavy ions are studied in the framework of a multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations. The model is verified on the example of the 136Xe + 209Bi system at several above barrier energies.

Modeling near-barrier collisions of heavy ions based on a Langevin-type approach

Background: Multinucleon transfer in low-energy nucleus-nucleus collisions is proposed as a method of production of yet-unknown neutron-rich nuclei hardly reachable by other methods.Purpose: Modeling of dynamics of nuclear reactions induced by heavy ions in their full complexity of competing reaction channels remains to be a challenging task. The work is aimed at development of such a model and its application to the analysis of multinucleon transfer in deep inelastic collisions of heavy ions leading, in particular, to formation of neutron-rich isotopes in the vicinity of the $N=126$ shell closure.Method: Multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations has been proposed. It is combined with a statistical model for simulation of de-excitation of primary reaction fragments. The model provides a continuous description of the system evolution starting from the well-separated target and projectile in the entrance channel of the reaction up to the formation of final reaction products.Results: A rather complete set of experimental data available for reactions $^{136}\mathrm{Xe}+^{198}\mathrm{Pt},^{208}\mathrm{Pb},^{209}\mathrm{Bi}$ was analyzed within the developed model. The model parameters have been determined. The calculated energy, mass, charge, and angular distributions of reaction products, their various correlations as well as cross sections for production of specific isotopes agree well with the data. On this basis, optimal experimental conditions for synthesizing the neutron-rich nuclei in the vicinity of the $N=126$ shell were formulated and the corresponding cross sections were predicted.Conclusions: The production yields of neutron-rich nuclei with $N=126$ weakly depend on the incident energy. At the same time, the corresponding angular distributions are strongly energy dependent. They are peaked at grazing angles for larger energies and extend up to the forward angles at low near-barrier collision energies. The corresponding cross sections exceed 100 nb for the nuclei located at the border of the known region, which is nearly five orders of magnitude larger than can be reached in the fragmentation reactions.

Quantal nucleon diffusion: Central collisions of symmetric nuclei

Quantal diffusion mechanism of nucleon exchange is studied in the central collisions of several symmetric heavy-ion collisions in the framework of the Stochastic Mean-Field (SMF) approach. Since at bombarding energies below the fusion barrier, di-nuclear structure is maintained, it is possible to describe nucleon exchange as a diffusion process familiar from deep-inelastic collisions. Quantal diffusion coefficients, including memory effects, for proton and neutron exchanges are extracted microscopically employing the SMF approach. The quantal calculations of neutron and proton variances are compared with the semi-classical results.

Multinucleon transfer inO16,18,F19+Pb208reactions at energies near the fusion barrier

Background: Nuclear reactions are complex, involving collisions between composite systems where many-body dynamics determines outcomes. Successful models have been developed to explain particular reaction outcomes in distinct energy and mass regimes, but a unifying picture remains elusive. The irreversible transfer of kinetic energy from the relative motion of the collision partners to their internal states, as is known to occur in deep inelastic collisions, has yet to be successfully incorporated explicitly into fully quantal reaction models. The influence of these processes on fusion is not yet quantitatively understood.Purpose: To investigate the population of high excitation energies in transfer reactions at sub-barrier energies, which are precursors to deep inelastic processes, and their dependence on the internuclear separation.Methods: Transfer probabilities and excitation energy spectra have been measured in collisions of $^{16,18}\mathrm{O},\phantom{\rule{0.16em}{0ex}}^{19}\mathrm{F}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}^{208}\mathrm{Pb}$, at various energies below and around the fusion barrier, by detecting the backscattered projectile-like fragments in a $\mathrm{\ensuremath{\Delta}}E\text{\ensuremath{-}}E$ telescope.Results: The relative yields of different transfer outcomes are strongly driven by $Q$ values, but change with the internuclear separation. In $^{16}\mathrm{O}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}^{208}\mathrm{Pb}$, single nucleon transfer dominates, with a strong contribution from $\ensuremath{-}2p$ transfer close to the Coulomb barrier, though this channel becomes less significant in relation to the $\ensuremath{-}2p2n$ transfer channel at larger separations. For $^{18}\mathrm{O}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}^{208}\mathrm{Pb}$, the $\ensuremath{-}2p2n$ channel is the dominant charge transfer mode at all separations. In the reactions with $^{19}\mathrm{F},\phantom{\rule{0.16em}{0ex}}\ensuremath{-}3p2n$ transfer is significant close to the barrier, but falls off rapidly with energy. Multinucleon transfer processes are shown to lead to high excitation energies (up to $\ensuremath{\sim}15$ MeV), which is distinct from single nucleon transfer modes which predominantly populate states at low excitation energy.Conclusions: Kinetic energy is transferred into internal excitations following transfer, with this energy being distributed over a larger number of states and to higher excitations with increasing numbers of transferred nucleons. Multinucleon transfer is thus a mechanism by which energy can be dissipated from the relative motion before reaching the fusion barrier radius.