Pb Targets Research Articles

Coulomb and nuclear interactions in the dynamics of weakly-bound neutron-halo breakup on heavy target * *LT acknowledge support from Conselho Nacional de Desenvolvimento Científico e Tecnológico [Procs. 304469-2019-0 and 464898/2014-5 (INCT-FNA)], and Fundação de Amparo à Pesquisa do Estado de São Paulo [Projs. 2017/05660-0]

Within our aim to clarify some aspects of the breakup dynamics of loosely-bound neutron-halo projectiles on a heavy target, we apply the continuum discretized coupled-channel formalism to investigate the beryllium 11Be breakup on a lead 208Pb target at = 140 MeV incident energy. By evidencing that the continuum–continuum couplings are much stronger in the nuclear breakup than in the Coulomb breakup, we conclude that the strength of these couplings in the total breakup is dominated by the nuclear contribution, with the diagonal monopole nuclear potential in the projectile–target center-of-mass having negligible effect on the total and nuclear breakup cross-sections. For this kind of reaction, we show that the condition for the total breakup to approach its dominant component in the absorption region is strongly dependent on the continuum–continuum couplings and the diagonal monopole nuclear potential.

Measurement of cross sections for charge pickup by 12C on elemental targets at 400 MeV/n

The nuclear charge pickup cross sections of 12C on CH2, C, Al, Cu, and Pb targets at the highest energy of 398 MeV/n were investigated using CR-39 nuclear track detector. The cross section for H was calculated from those measured on C and CH2 targets. The dependence of charge pickup cross section on target mass was investigated, it was found that the nuclear charge pickup cross section is linearly depended on the target mass. This linear dependence is consistent with the prediction of nuclear peripheral and surface collision of charge pickup.

Measurement of cross-sections for charge pickup by 12C on elemental targets at 290MeV/n

The nuclear charge pickup cross-sections of [Formula: see text]C on CH2, C, Al, Cu and Pb targets at the highest energy of 288[Formula: see text]MeV/n were investigated using CR-39 nuclear track detector. The cross-section for H was calculated from those measured on C and CH2 targets. The dependence of charge pickup cross-section on target mass was investigated. It was found that the nuclear charge pickup cross-section of [Formula: see text]C at our studied beam energies seems to exponentially depend on the target mass with the fitting exponent [Formula: see text], which can be well explained by the peripheral and the surface collisions of the nuclear charge pickup reactions.

Folding model analysis of 28Si elastic scattering using different density distributions

The elastic scattering cross-sections of [Formula: see text]Si projectile by [Formula: see text]Al, [Formula: see text]Si, [Formula: see text]Ni, [Formula: see text]Ni and [Formula: see text]Pb targets are analyzed using the double folding model based on the effective M3Y interaction which is known as the most popular density independent form. In the calculations of the double folding model, 16 different density distributions of [Formula: see text]Si nucleus are examined. A very good agreement between experimental data and theoretical results is obtained, and also the literature results support our results. In addition, dependence on incident energy, target atomic number and target mass number of the imaginary potential depth is studied, and new and global equations are proposed.

Structure and properties of TiN–Pb composite coatings deposited on VT6 alloy by DC magnetron sputtering

DC reactive magnetron sputtering of two separate single-element Ti and Pb targets was used to deposit a TiN–Pb composite coating onto a substrate made of the VT6 titanium alloy. The studies were carried out at Pb cathode currents of 0.2 and 0.1 A and two fixed argon flow rate values of 6.0 or 8.5 cm3/min, and the flow rate of nitrogen supplied to the chamber varying from experiment to experiment. The composition of coatings was determined by energy dispersive analysis. It was shown that the amount of lead in the coatings ranged from 0.5 to 16 wt.% depending on the Pb cathode current and reactive nitrogen consumption. Coating microhardness and wear were determined for each deposition mode. It was found that coating thicknesses varied from 1.9 to 5.2 μm depending on the ratio of argon and nitrogen fluxes. The effect of TiN–Pb magnetron coating deposition parameters on the structure and phase composition was investigated by X-ray diffraction method. It was shown that the coating consists of Pb and PbO at the Pb cathode current of 0.2 A, and of TiN, Pb, and PbO at the current of 0.1 A, while an increase in the ratio of argon and nitrogen fluxes leads to an increase in the fraction of TiN, the intensity of titanium substrate surface saturation with nitrogen, as well as microhardness and wear resistance. Under all deposition conditions the TiN coating features by a typical texture (111), the intensity of which varies nonmonotonically.

Observation of He6+t cluster states in Li9

$^{6}$He+$t$ cluster states of exited $^{9}$Li have been measured by 32.7 MeV/nucleon $^{9}$Li beams bombarding on $^{208}$Pb target. Two resonant states are clearly observed with the excitation energies at 9.8 MeV and 12.6 MeV and spin-parity of 3/2$^{-}$ and 7/2$^{-}$ respectively. These two states are considered to be members of K$^{\pi}$=1/2$^{-}$ band. The spin-parity of them are identified by the method of angular correlation analysis and verified by the continuum discretized coupled channels (CDCC) calculation, which agrees with the prediction of the generator coordinate method (GCM). A monopole matrix element about 4 fm$^{2}$ for the 3/2$^{-}$ state is extracted from the distorted wave Born approximation (DWBA) calculation. These results strongly support the feature of clustering structure of two neutron-rich clusters in the neutron-rich nucleus $^{9}$Li for the first time.

Sub-barrier fusion of 34,36S+204,206,208Pb: Signature of isotopic dependence of repulsive core potential in heavy-ion fusion reactions

The measurements of the excitation function for the heavy-ion fusion-fission cross sections in negative Q-value systems 34S+204,206,208Pb and 36S+204,206,208Pb have been analyzed by coupled-channels (CC) calculations based on the M3Y double-folding (DF) potential that is supplemented with a short-ranged repulsive potential. The standard Aage Winther potential is also employed to explore the occurrence of the unexpected steep fall-off phenomenon of the measured cross sections in fusion between sulfur and lead nuclei. Our analysis based on the deep phenomenological potentials clearly demonstrates that the fusion data are strongly hindered at incident energies well below the Coulomb barrier for the four heavy-ion systems 34S+206Pb, 34S+208Pb, 36S+206Pb and 36S+208Pb. In addition, a first indication of a maximum in the trend of the experimental data of the S-factor representation has been observed for each of the fusions of 34,36S with 206,208Pb targets. It is shown that the M3Y+Repulsion potential accompanied by the CC calculations provides a satisfactory description of the experimental fusion cross sections and S factors in the whole energy range under study for all the six cases of interest. A discussion is also presented concerning the isotopic dependence of the parameters existing in simulation of the repulsive core potential. Our detailed study reveals that the strength of the repulsive interaction and incompressibility of the nuclear matter (NM) increases and decrease linearly with addition of neutrons in the isotopic systems, respectively. Further, we show that the repulsive part of the density distribution becomes more diffuse with increasing neutrons from 34S+204Pb to 36S+208Pb.

Systematic study on the role of various higher-order processes in the breakup of weakly-bound projectiles

Abstract The virtual photon theory (VPT), which is based on first-order Coulomb dissociation restricted to the electric dipole (E1), has been successfully used to explain the breakup data for several cases. Our aim is to study the role of various higher-order processes that are ignored in the VPT, such as the nuclear breakup, interference between nuclear and Coulomb amplitudes, and multistep breakup processes mainly due to strong continuum-continuum couplings in the breakup of two-body projectiles on a heavy target at both intermediate and higher incident energies. For the purpose of numerical calculations, we employed eikonal version of three-body continuum-discretized coupled-channels (CDCC) reaction model. Our results for the breakup of 11Be and 17F on 208Pb target at 100, 250, and 520 MeV/A, show the importance of nuclear breakup contribution, and its significant role in the multistep processes. The multistep effect on Coulomb breakup for core-neutron projectile was found to be negligible, whereas it was important for core-proton projectile. Coulomb-nuclear interference (CNI) effect was also found to be non-negligible. Qantitatively, the multistep effects due to the nuclear breakup was found to depend on the incident energy through the energy dependence of the core-target and nucleon-target nuclear potentials. The nuclear breakup component, the CNI effect, and the multistep breakup processes are all found to be non-negligible; hence, the assumptions adopted in the VPT for the accurate description of breakup cross sections are not valid.

An Analysis of Elastic Scattering Angular Distributions of $$^{17}$$F on a $$^{208}$$Pb Target at Different Energies

This study investigated the elastic scattering of a $$^{\mathrm {17}}$$ F $$+^{\mathrm {208}}$$ Pb system at different energies using the Continuum-Discretized Coupled Channels (CDCC) method. A microscopic optical model was selected and double-folding potential was used for the $$^{\mathrm {16}}$$ O $$+$$ target interaction. The real part of the optical model was determined as folding potential and the imaginary part of the optical model was taken as standard volume Woods–Saxon shape. Single-channel and multi-channel CDCC calculations were performed to determine the effect of excited channels. An elastic scattering cross section of the $$^{\mathrm {17}}$$ F $$+^{\mathrm {208}}$$ Pb system was calculated and its compatibility with experimental data was determined.

Production of super-heavy nuclei in cold fusion reactions

A model for cold-fusion reactions related to the synthesis of super-heavy nuclei in collisions of heavy projectile-nuclei with a 208Pb target nucleus is discussed. In the framework of this model, the production of the compound nucleus by two paths, the di-nuclear system path and the fusion path, are taken into account simultaneously. The formation of the compound nucleus in the framework of the di-nuclear system is related to the transfer of nucleons from the light nucleus to the heavy one. The fusion path is linked to the sequential evolution of the nuclear shape from the system of contacting nuclei to the compound nucleus. It is shown that the compound nucleus is mainly formed by the fusion path in cold-fusion reactions. The landscape of the potential energy related to the fusion path is discussed in detail. This landscape for very heavy nucleus-nucleus systems has an intermediate state, which is linked to the formation of both the compound nucleus and the quasi-fission fragments. The decay of the intermediate state is taken into account in the calculation of the compound nucleus production cross sections and the quasi-fission cross sections. The values of the cold-fusion cross sections obtained in the model agree well with the experimental data.

Reactive magnetron sputtering of TiN-Pb coatings using two metal targets

One of the promising areas of application of the magnetron co-sputtering method using two separate targets in a reactive atmosphere is to increase the tribological properties of friction pairs by applying composite solid lubricant coatings consisting of a solid matrix and a soft lubricant. In this paper, we study the dependence of the parameters of TiN-Pb coatings obtained by co-spraying of separate Ti and Pb targets in a mixture of Ar and N gases on pressure. The factors that have a significant impact on the process of coating deposition were also determined.

Elastic scattering angular distributions of neutron halo nucleus $$^{11}$$Be studied via dynamic polarization potentials

Cluster aspects of the nuclear structure manifest themselves in, among many other types of nuclear reactions, the breakup reactions of weakly-bound nuclei and their couplings with the other reaction channels. In the present work we analyzed the breakup coupling effects to the elastic scattering angular distributions of $$^{11}$$ Be with a $$^{208}$$ Pb target at an incident energy of 140 MeV. Weighted mean local polarization potentials (WMLPPs), which mimic the dynamic polarization potentials (DPPs) induced by the breakup coupling effects to the elastic scattering channel, were obtained from continuum discretized coupled channel (CDCC) calculations. Suppression of the Coulomb-nuclear interference peaks (CNIPs) of the elastic scattering angular distributions is found to be caused by the destructive interference between the Coulomb and the Coulomb-distorted nuclear amplitude due to the WMLPPs. Comparisons between the WMLPPs and the theoretically calculated Coulomb dipole polarization potentials (CDPPs) suggest that the breakup coupling effect of the $$^{11}$$ Be+ $$^{208}$$ Pb system cannot be represented by the CDPPs alone.

Energy and angular distribution of photo-neutrons for 16.6 MeV polarized photon on medium–heavy targets

The energy spectra as well as the angular distribution of photo-neutrons, called the double differential cross sections (DDXs) of the (γ, xn) reaction were measured for 16.6 MeV linearly polarized photons on Pb, Au, Sn, Cu, Fe, and Ti targets. Polarized photons were prepared using the laser Compton scattering technique at BL01, NewSUBARU, Hyogo, Japan. The photo-neutrons were measured using liquid organic scintillators, placed at six different angles. The time-of-flight technique was used to determine the neutron energy. The low energy and high energy components on the DDXs were identified for all the targets. Flat angular dependence was observed for the low energy component; however, a cos(2Θ) distribution was observed for the high energy component, where Θ is the angle between the photon polarization direction and neutron emission. The angular dependences were parameterized by fitting the experimental data. The obtained parameters were compared with those from previous studies conducted decades ago.

Direct processes for the systems 7Be,8B + 208Pb at Coulomb barrier energies

The elastic scattering process for the nuclear reactions induced by the Radioactive Ion Beams 7Be and 8B on a 208Pb target was measured for the first time in the energy range around the Coulomb barrier. Extensive theoretical calculations within the framework of the optical model were performed. An excellent agreement between experimental data and theoretical predictions was achieved for the reaction 7Be + 208Pb, while a comprehensive understanding of the reaction dynamics induced by the more exotic projectile 8B is still far to be reached. Predictions of the cross section for the breakup for both systems will also be given.

Study of the scattering of 15C at energies around the Coulomb barrier

The neutron rich carbon isotope 15C is the only known case of an almost “pure” 2s1/2 single-neutron halo ground state configuration. At collision energies around the Coulomb barrier the reaction dynamics is expected to be dominated by single neutron transfer and breakup. To investigate these effects, we have measured the scattering of 15C with a 208Pb target at 65 MeV at the HIE-ISOLDE facility in CERN (Geneva, Switzerland). The preliminary data demonstrates the presence of a strong long-range absorption pattern in the angular distribution of the elastic cross section. The results are discussed in the framework of Optical Model calculations.

Scattering of the halo nucleus 11Be from a lead target at 3.5 times the Coulomb barrier energy

Angular distributions of quasielastic scattering and breakup of the neutron-rich halo nucleus 11Be on a 208Pb target at an incident energy of 140 MeV (about 3.5 times the Coulomb barrier) were measured at HIRFL-RIBLL. A strong suppression of the Coulomb nuclear interference peak is observed in the measured quasielastic scattering angular distribution. The result demonstrates for the first time the persistence of the strong breakup coupling effect reported so far for reaction systems involving neutron-halo nuclei at this relatively high incident energy. The measured quasielastic scattering cross sections are satisfactorily reproduced by continuum discretized coupled channel (CDCC) calculations as well as by the XCDCC calculations where the deformation of the 10Be core is taken into account. The angular and energy distributions of the 10Be fragments could also be well reproduced considering elastic breakup (CDCC and XCDCC) plus nonelastic breakup contributions, with the latter evaluated with the model by Ichimura, Austern and Vincent [1]. The comparison of the 10Be energy distributions with simple kinematical estimates evidence the presence of a significant post-acceleration effect which, in the (X)CDCC frameworks, is accounted for by continuum-continuum couplings.

Calculation and verification for energetic proton energy deposition in spallation target

Energy deposition in spallation target induced by energetic protons is the foundation and the premise of the spallation target research. In this paper, several intra-nuclear cascade models including BERTINI, ISABEL, CEM2K and INCL4 contained in MCNPX package, together with FLUKA and PHITS Monte Carlo codes are used to calculate the energy deposition in lead (Pb) and tungsten (W) spallation target impinged by 800, 1000, and 1200 MeV protons. The contributions of different particles to the total energy deposition in the Pb target are obtained and compared with each other as well. The energy deposition distribution caused by 250 MeV protons in the W target is measured with thermoluminescence detectors (TLDs). The results indicate that the calculations from the MCNPX accord with experimental data, verifying that the Monte Carlo code has a high reliability for energy deposition simulation.

Analysis of Fusion Cross Sections in the 9Be Projectile Breakup on Different Target Nuclei

We present a theoretical study of total fusion (TF), complete fusion (CF), and incomplete fusion (ICF) cross sections in the breakup of 9Be (described as n −8Be) projectile on 124Sn, 144Sm and 208Pb target nuclei. We use the continuum discretized coupled-channel formalism together with a sum-rule model, by extending an approach outlined in Mukeru et al. (Nucl. Phys. A 996:121700, 2020) to another weakly bound projectile in different targets. The applicability of the model to incident energies below and around the Coulomb barrier is verified, being confirmed for all three reactions an empirical energy-dependent cutoff angular momentum expression. We show that the TF and ICF cross sections are strongly dependent on the projectile binding energy eb, whereas the CF is weakly affected by that. Despite this weak dependence, the CF contribution to the TF cross section becomes more suppressed by decreasing eb. The dependence of the ICF probability on the breakup threshold is also highlighted.

Multi-neutron transfer in He8 -induced reactions near the Coulomb barrier

The measured inclusive $^6$He and $^4$He production cross sections of G. Marqu{\'i}nez-Dur{\'a}n {\em et al.}, Phys.\ Rev.\ C {\bf 98}, 034615 (2018) are reexamined and the conclusions concerning the relative importance of 1n and 2n transfer to the production of $^6$He arising from the interaction of a 22 MeV $^8$He beam with a $^{208}$Pb target revised. A consideration of the kinematics of the 2n-stripping reaction when compared with the measured $^6$He total energy versus angle spectrum places strict limits on the allowed excitation energy of the $^{210}$Pb residual, so constraining distorted wave Born approximation calculations that the contribution of the 2n stripping process to the inclusive $^6$He production can only be relatively small. It is therefore concluded that the dominant $^6$He production mechanism must be 1n stripping followed by decay of the $^7$He ejectile. Based on this result we present strong arguments in favor of direct, one step four-neutron (4n) stripping as the main mechanism for $^4$He production.

Methods for centrality determination in nucleus-nucleus collisions with forward hadron calorimeters at the BM@N experiment

The BM@N (Baryonic Matter at Nuclotron) is the fixed target experiment at the Nuclotron (JINR, Dubna, Russia) accelerator complex. The main goal of the BM@N experiment is studying properties of dense nuclear matter produced in the ion-ion collisions at beam energies up to 4.5 AGeV. First experiments were done for carbon, argon and krypton ions beams with C, Al, Cu and Pb targets. The methods of central events selection on event-by-event base with ZDC (Zero Degree Calorimeter) for these reactions are presented. The new Forward Hadron Calorimeter (FHCal) with transverse and longitudinal segmentation will be used to measure the collision centrality in heavy ion experiments after the BM@N upgrade. The FHCal has the beam hole in the center due to expected high beam intensities. New forward quartz hodoscope is been developed to be placed in the beam hole to measure the charge of fragments. New methods of centrality determination with the FHCal and forward quartz hodoscope are discussed.