Medium Mass Targets Research Articles

Theoretical analysis of light and heavy-ion induced reactions: production of medically relevant 97Ru

Abstract 97Ru is a key radionuclide sought for diagnostic imaging due to its low-energy and intense γ-rays of 215.7 keV and 324.5 keV. New reaction routes to produce this radionuclide are constantly being investigated. A crucial step in carrying out such reactions is a reliable beforehand estimate of the production cross section of radionuclide and optimization conditions through robust theoretical frameworks. Existing literature on α + 95Mo reaction has been freshly examined to understand the excitation function of 97Ru. The data have been compared to other reactions of different projectiles on medium-mass targets. The reaction codes pace4, empire-3.2.2, and talys-1.96 have been employed to decipher the reaction mechanism and check the predictive ability of underlying theoretical models. The yield of 97Ru at different projectile energies and thick target yield in the optimum energy range has also been determined from the theoretical modeling.

Sub-barrier fusion dynamics in 28,30Si induced reactions with medium mass targets

The state-of-the-art technologies made it possible to reach the realms of fusion between two complex nuclei that offer an opportunity to explore a diverse spectrum of fusion phenomena. In this article, we have reported the influence of positive Q-value neutron transfer (PQNT) channels in fusion dynamics. Significant enhancement in sub-barrier fusion cross section has been observed for the 28Si+158Gd as compared to 30Si+140Ce and other similar systems with nearby mass asymmetry. Current findings include a comparison of the fusion excitation function of multiple systems on a reduced scale. The study sheds light on the influence of PQNT channels and deformation in nuclei on the sub-barrier fusion phenomenon. Further, fusion barrier parameters (barrier height and radius) extracted from the measured data demonstrate a good agreement with the empirical parameterization and proximity potential models.

Analysis of fusion reactions induced by weakly bound nuclei on medium and heavy mass targets

Fusion cross section for reactions induced by weakly bound nuclei 6He, 6,7Li 9,11Be and 10B on targets lying in the mass region 64 ≤ A ≤ 238 have been investigated at around Coulomb barrier energies within the coupled channel formalism. Specifically, the effects of coupling to low-lying excited states of reactants and those arises due to the breakup of projectile have been studied by using Broglia and Winther (BW91), Aage Winther (AW95) and fitted potential (FP) parameterization schemes. Among these the FP scheme is found to be most appropriate in the description of fusion excitation functions of various projectile-target combination. Further, it is observed that in the sub barrier energy region there is an enhancement in the fusion cross section due to coupling to excited states while there occurs fusion suppression at above barrier energies because of the breakup of the projectile.

Threshold anomalies in low-energy reactions with loosely-bound projectiles

Recent results concerning data for fusion and elastic scattering of low-energy neutron-halo 6He and weakly-bound 6Li projectiles, colliding with medium mass targets, are briefly reviewed. The extended optical model (EOM) was used, which includes two complex polarization potentials, one associated to fusion couplings and the other one associated to direct reaction couplings. Four systems having 6Li projectiles and one with 6He were analyzed. The extracted threshold anomalies are discussed.

Production of high-energyγrays in proton- andα-induced reactions

The high-energy $\ensuremath{\gamma}$ rays have been measured in proton and $\ensuremath{\alpha}$-induced reactions on medium mass target nuclei $^{115}\mathrm{In}$ and $^{112}\mathrm{Sn}$, respectively. Theoretical analyses of the spectra have been performed within the Hauser-Feshbach statistical model and the Akkermans-Gruppelaar exciton model formalisms. It is observed that the proton-induced reaction has significant contribution from the direct-semidirect capture in the region ${E}_{\ensuremath{\gamma}} \ensuremath{\approx}10--20$ MeV. The $^{4}\mathrm{He}$-ion-induced reaction could be described reasonably well by the results of the statistical model calculations. A reduced level density parameter, as compared to that used for the proton-induced reaction, was required to explain the high-energy $\ensuremath{\gamma}$-ray spectrum in the $^{4}\mathrm{He}$-ion-induced reaction.

Coupled channels effects in heavy ion reactions

The ECIS (Equations Couplees Iterations Sequentielles) code of Jacques Raynal continues to have an important role since its first version in the seventies. Its use to describe the elastic and inelastic scattering of light heavy ions at energies close to the Coulomb barrier is the first topic of this paper. Nuclear reactions with weakly bound stable and radioactive projectiles are described in the second topic, where the projectiles breakup is not taken into account in ECIS and a more recent formalism called Continuum Discretized Coupled Channels (CDCC) calculations is applied to them. The second topic also contains some results that were obtained at the Radioactive Ion Beams in Brasil (RIBRAS) facility, with a radioactive 2n-halo $$^6$$ He beam on light, medium mass, and heavy targets.

Barrier distribution for the weakly bound stable projectile Li7 with the medium-mass target nucleus Ni64

Barrier distribution for the weakly bound stable projectile <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Li</mml:mi><mml:mprescripts /><mml:none /><mml:mn>7</mml:mn></mml:mmultiscripts></mml:math> with the medium-mass target nucleus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ni</mml:mi><mml:mprescripts /><mml:none /><mml:mn>64</mml:mn></mml:mmultiscripts></mml:math>

Dynamical versus statistical production of Intermediate Mass Fragments at Fermi Energies

The emission probability of Intermediate Mass Fragments (IMFs) in non-central reactions has been investigated in collisions of heavy $$^{124}\hbox {Xe}$$ projectiles with the two different medium-mass targets of $$^{64}\hbox {Ni}$$ and $$^{64}\hbox {Zn}$$ at the laboratory energy of 35 A MeV. The two colliding systems differ only for the target atomic number Z and, consequently, for the isospin N/Z ratio. The probability of IMFs emission from the projectile-like fragment has been measured, showing an enhancement of the IMFs emission for the neutron rich $$^{64}\hbox {Ni}$$ target. Most of the observed projectile break-up yield is associated with the production of only one IMF, that is, a quasi-binary splitting of projectile in two fragments in a broad range of charge asymmetry. For the events with one IMF, the relative contributions of the dynamical and statistical emissions have been evaluated. We find an enhancement of dynamical break-up probability for the neutron rich target with respect to the neutron poor one. The analysis suggests influence of the target isospin in inducing the dynamical break-up of projectile-like fragments. The new data have been also compared with previous published results of $$^{112,124}\hbox {Sn}$$ + $$^{58,64}\hbox {Ni}$$ systems, in order to disentangle between isospin effects against system-size effects on the emission probability. The comparisons between previous and new data suggest that the dynamical break-up is determined by the N/Z content of both projectile and target; for the cases here investigated, the influence of the system size on the dynamical emission probability can be excluded.

Charge exchange reactions on medium and heavy mass targets at intermediate energies

The nuclear isotopic structure can be understood easily via the intermediate-energy charge exchange reactions of (p, n) and [Formula: see text]He, [Formula: see text] type. In the current contribution, we present some results for charge exchange reactions induced by 3He on targets lying in mass region [Formula: see text] within the theoretical framework of plane wave impulse approximation (PWIA) and distorted wave impulse approximation (DWIA). Here, the recoil effects in PWIA have also been considered. Particularly, the angular distributions and the unit cross-sections have been calculated and compared with the available data. Further, the importance of inclusion of the exchange contribution in these reactions is also considered, which eventually enhance the matching with data.

Elastic backscattering measurments for 6,7Li+58Ni, 6,7Li+116,120Sn, 6,7Li+208Pb at near barrier energies

We have performed, elastic backscattering measurements for the weakly bound nuclei 6,7Li on the medium and heavy mass targets 58Ni, 116,120Sn, 208Pb at sub- and near-barrier energies (0.6 to 1.3 EC.b.). Excitation functions of elastic scattering cross sections have been measured at 160O and 170O and the corresponding ratios to Rutherford scattering and relevant barrier distributions have been extracted. These measurements will complement recent work on a 28Si target for probing the potential at sub- and near barrier energies and relevant reaction mechanisms.

Systematic study of elastic scattering and fusion induced by weakly bound 6Li on medium mass targets. Threshold anomalies

Using the extended optical model, a comparative and systematic analysis of different 6Li-induced reactions at sub- and above-barrier energies is carried out. Collisions with 58Ni, 59Co, 64Ni and 64Zn are analyzed. For each selected system, the São Paulo potential is used as a bare potential, a surface polarization potential is added to simulate the effects of direct reactions and a volume potential is considered to account for couplings to fusion. Simultaneous fits to the corresponding elastic scattering and fusion data of each system are optimized at the different energies measured, and the validity of the respective dispersion relations is verified. Based on the potentials obtained for each selected system, the elastic scattering data are properly described and the fusion cross sections are well reproduced at the energies around and above the barrier. For the 6Li + (58Ni, 64Zn) systems, some abnormal strength values are found for the fusion polarization potentials at sub-barrier energies, which would invalidate the dispersion relation. A possible explanation is put forward and, as a result, it is concluded that the constriction of dispersive potentials might help identify unphysical data. For all systems, the final energy dependence of the surface polarization potential is found to be consistent with the Breakup Threshold Anomaly, while the fusion polarization potential follows the Threshold Anomaly.

Influence of coupling of excited states and of deuteron transfer on fusion reactions induced by 6,7Li on 64Ni, 152Sm and 209Bi targets

Here, we present a comprehensive analysis of fusion reaction data induced by weakly bound nuclei 6,7Li on medium and heavy mass targets 64Ni, 152Sm and 209Bi at around Coulomb barrier energies within the framework of coupled channel method. Particularly, the influence of coupling of various excited states of the colliding nuclei and the deuteron transfer effects on fusion excitation function have been investigated. It is found that the inclusion of coupling effects leads to an enhancement up to 74% in fusion reaction cross section in close vicinity of Coulomb barrier when compared with one dimensional barrier penetration model predictions. However the inclusion of deuteron transfer effects reduces this enhancement up to 23% in below barrier region while up to 36% in above barrier energy region and reproduces the data reasonably well.

Microscopic analysis of elastic scattering cross sections for different densities of $^{8}$Li nucleus on light, medium and heavy mass targets

The elastic scattering angular distributions of weakly bound nucleus$^{8}$Li on $^{7}$Li, $^{9}$Be, $^{12}$C, $^{13}$C, $^{14}$N,$^{27}$Al, $^{51}$V, $^{58}$Ni, and $^{208}$Pb are analyzed atvarious incident energies. For this purpose, the real potential isgenerated for nine different density distributions of the $^{8}$Linucleus by using the double folding model within the optical model.The theoretical results are in good agreement with the experimentaldata. In our study, also, new and practical sets of imaginarypotentials for the investigated densities are derived.

Energy evolution of channel coupling for the system Li6+Ni64 at near-barrier energies

Background: Different theoretical models have been used to understand the effects of coupling of direct reaction channels on reaction observables in recent years. However, very few attempts have been made to check the consistency of the model calculations in terms of comparing different experimental observables with the model predictions.Purpose: In the present work, coupled channel calculations are performed with transfer and breakup coupling for collision of the weakly bound stable projectile $^{6}\mathrm{Li}$ with the medium-mass target $^{64}\mathrm{Ni}$ at near-barrier energies. The main goal is to find the consistency of the model calculation in simultaneous reproduction of reaction observables like the elastic angular distributions, back-angle elastic excitation function, and fusion excitation function to find the effective energy regions of dominance of these couplings.Method: Both coupled reaction channel (CRC) and continuum discretized coupled channel (CDCC) calculations are performed using the code fresco. Transfer coupling is included through the CRC formalism. The CDCC scheme is used for breakup coupling and to distinguish the effect of resonant and nonresonant couplings.Results: In the case of the CRC calculation, the full coupling including inelastic scattering, $1n$ stripping, and $1p$ stripping gives the best description of the experimental data and particularly reproduces the data in the subbarrier energy region. It is observed that the $1p$-transfer channel has a larger impact on reaction observables compared to $1n$ transfer. On the other hand, for breakup nonresonant breakup has the dominant effect on the reaction observables, although resonant breakup has a larger cross section. The full breakup coupling reproduces the elastic scattering angular distributions and excitation function in the above-barrier region. But the scheme overpredicts these observables in the subbarrier region.Conclusion: CRC and CDCC calculations are complementary to each other. The energy dependencies of the relevant couplings for the $^{6}\mathrm{Li}+^{64}\mathrm{Ni}$ system around the barrier show that inelastic and transfer coupling are important at energies below the Coulomb barrier but continuum coupling is dominant in the above-barrier energy region.

Elastic and inelastic scattering for the B10+Ni58 system at near-barrier energies

Full angular distributions of the $^{10}\mathrm{B}$ elastically and inelastically scattered by $^{58}\mathrm{Ni}$ have been measured at different energies around the Coulomb barrier. The elastic and inelastic scattering of $^{10}\mathrm{B}$ on a medium mass target has been measured for the first time. The obtained angular distributions have been analyzed in terms of large-scale coupled reaction channel calculations, where several inelastic transitions of the projectile and the target, as well as the most relevant one- and two-step transfer reactions have been included in the coupling matrix. The roles of the spin reorientation, the spin-orbit interaction, and the large ground-state deformation of the $^{10}\mathrm{B}$, in the reaction mechanism, were also investigated. The real part of the interaction potential between projectile and target was represented by a parameter-free double-folding potential, whereas no imaginary potential at the surface was considered. In this sense, the theoretical calculations were parameter free and their results were compared to experimental data to investigate the relative importance of the different reaction channels. A striking influence of the ground-state spin reorientation of the $^{10}\mathrm{B}$ nucleus was found, while all transfer reactions investigated had a minimum contribution to the dynamics of the system. Finally, the large static deformation of the $^{10}\mathrm{B}$ and the spin-orbit coupling can also play an important role in the system studied.

Optical model potentials for He6+Zn64 from Cu63(Li7,He6)Zn64 reactions

Angular distributions of the transfer reaction $^{63}\mathrm{Cu}(^{7}\mathrm{Li},^{6}\mathrm{He})^{64}\mathrm{Zn}$ were measured at ${E}_{\mathrm{lab}}(^{7}\mathrm{Li})=12.67$, 15.21, 16.33, 23.30, 27.30, and 30.96 MeV. With the interaction potentials of the entrance channel $^{7}\mathrm{Li}+^{63}\mathrm{Cu}$ obtained from elastic scattering data as input, the optical potentials of the halo nuclear system $^{6}\mathrm{He}+^{64}\mathrm{Zn}$ in the exit channel were extracted by fitting the experimental data with the distorted-wave Born approximation (DWBA) and coupled reaction channels (CRC) methods, respectively. The results show that the threshold anomaly presents in the weakly bound system of $^{7}\mathrm{Li}+^{63}\mathrm{Cu}$ and the dispersion relation can be adopted to describe the connection between the real and imaginary potentials, while both the real and imaginary potentials nearly keep constant within the researched energy region for the halo system of $^{6}\mathrm{He}+^{64}\mathrm{Zn}$. Moreover, calculations by the potentials extracted from the CRC method can reproduce the experimental elastic scattering of the $^{6}\mathrm{He}+^{64}\mathrm{Zn}$ system rather well, but those by the potentials from the DWBA method cannot, where the couplings between $^{7}\mathrm{Li}$ and $^{6}\mathrm{He}$ are absent. This work verifies the validity of the transfer method in the medium-mass target region and lays a solid foundation for the further study of optical potentials for exotic nuclear systems.

Study of breakup and transfer of weakly bound nucleus 6Li to explore the low energy reaction dynamics

Investigation of the breakup and transfer effect of weakly bound nuclei on the fusion process has been an interesting research topic in the past several years. However, owing to the low intensities of the presently available radioactive ion beam (RIB), it is difficult to clearly explore the reaction mechanisms of nuclear systems with unstable nuclei. In comparison with RIB, the beam intensities of stable weakly bound nuclei such as 6,7 Li and 9 Be, which have significant breakup probability, are orders of magnitude higher. Precise fusion measurements have already been performed with those stable weakly bound nuclei, and the effect of breakup of those nuclei on the fusion process has been extensively studied. Those nuclei indicated large production cross sections for particles other than the α + x breakup. The particles are originated from non-capture breakup (NCBU), incomplete fusion (ICF) and transfer processes. However, the conclusion of reaction dynamics was not clear and has the contradiction.In our previous experiments we have performed 6 Li+96 Zr and 154 Sm at HI-13 Tandem accelerator of China Institute of Atomic Energy (CIAE) by using HPGe array. It is shown that there is a small complete fusion (CF) suppression on medium-mass target nucleus 96 Zr different from about 35% suppression on heavier target nucleus 154 Sm at near-barrier energies. It seems that the CF suppression factor depends on the charge of target nuclei. We also observed one neutron transfer process. However, the experimental data are scarce for medium-mass target nuclei.In order to have a proper understanding of the influence of breakup and transfer of weakly bound projectiles on the fusion process, we performed the 6 Li+89 Y experiment with incident energies of 22 MeV and 34 MeV on Galileo array in cooperation with Si-ball EUCLIDES at Legnaro National Laboratory (LNL) in Italy. Using particle-particle and particle-γ coincidences, the different reaction mechanisms can be clearly explored.

Understanding the effect of channel coupling on fusion of6Li+64Ni

The effect of inelastic excitation and single particle transfer reactions on fusion have been investigated for the system 6 Li+ 64 Ni at near barrier energies. The calculations show that a simultaneous coupling to the inelastic excitation of projectile and target along with positive Q-value 1n- and 1p-stripping channels, describes the experimental CF cross sections reasonably well in the below barrier region. Exploring the interplay of different reaction channels in the collision of weakly bound systems is a subject of interest, both experimentally and theoretically, over the past several years [1–4]. In a recent work [5], the effect of coupling to inelastic excitations and single particle transfer channels on the back angle quasi-elastic excitation function had been reported for the system 6 Li+ 64 Ni. To investigate the effect of these couplings on fusion excitation function, a complementary experimental observable, for 6 Li+ 64 Ni is the primary motivation of the present work. Unlike the heavy targets, for the lower medium mass targets like 64 Ni the measured fusion cross sections with weakly bound projectiles provide total fusion (TF) cross sections instead of the cross sections for complete fusion (CF) of the whole projectile. The TF cross section for 6 Li+ 64 Ni system includes along with CF cross section the contributions from incomplete

Elastic and inelastic scattering for theB11+Ni58system: Target and projectile reorientation effects

Full angular distributions for elastic and inelastic scattering of $^{11}\mathrm{B}$ on $^{58}\mathrm{Ni}$ have been measured at different bombarding energies around the Coulomb barrier. Measurement and analysis with coupled-channel calculations have been performed for the first time for a system with the tightly bound $^{11}\mathrm{B}$ as projectile on a medium mass target. In these calculations, the real part of the interaction potential between nuclei was represented by a parameter-free double-folding potential. To avoid the use of an imaginary potential at the surface, several inelastic transitions of the projectile and the target have been included in the coupling matrix. The result of these coupled-channel calculations are in very good agreement with all experimental angular distributions. The most important result was the striking influence on the reaction mechanism of the ground-state-spin reorientation of the $^{11}\mathrm{B}$ nuclei.

Elastic Scattering of Neutron Halo Projectiles

Elastic scattering angular distributions of 6He on light, medium and heavy mass targets have been analysed using a simple diffractive model for the S-matrix. The results show that a very large diffuseness in the angular momentum space is necessary to reproduce the data in the case of scattering on heavy targets.