Neutron Transfer Research Articles

Neutron periphery in light nuclei

A spatial configuration of light nuclei that involves two excess neutrons (6He, 10Be, and 12B) is studied by analyzing cross sections for various reactions on these nuclei: 6He(α, α)6He, 9Be(d, p)10Be, and 10B(t, p)12B. Pole dineutron-transfer mechanisms (dineutron configuration of the neutron periphery) and second-order mechanisms involving sequential neutron transfer (cigar-like configuration of the neutron periphery) are taken into account in the calculations. It is shown that the neutron periphery is drastically different in the nuclei in question: in 6He, there is a halo receiving a contribution from both configurations; in 10Be, there is an only slightly noticeable halo featuring a contribution of practically one neutron from the cigar-like configuration; and, in 12B, there is a neutron skin.

Reaction functions for weakly bound systems

We propose a new technique to analyze total reaction cross sections. In this technique, which has been previously applied to fusion reactions, the experimental data are used to build a dimensionless reaction function, which does not depend on the system size or details of the optical potential. In this way, total reaction cross sections for different systems can be directly compared. We employ this technique to perform a systematic study of reaction cross sections of weakly bound systems in different mass ranges, and compare their reaction functions with the ones of tightly bound systems with similar masses. We show that breakup reactions and neutron transfers in halo systems lead to large reaction functions, well above the ones of typical tightly or weakly bound stable systems.

Understanding fusion suppression and enhancement in the 18O + 58,60,64Ni systems

Realistic coupled-channel calculation results for the 18[O] + 58,60,64Ni systems in the bombarding energy range 34.5 ⩽ E Lab ⩽ 65 MeV are presented. The overall agreement with existing experimental data is quite good. Our calculations predict an unexpected fusion suppression for above-barrier energies, with an important contribution of the two neutron ( 18O, 16O) transfer channel couplings. The sub-barrier fusion enhancement and the above barrier suppression, predicted by the calculations, are consistent with the nuclear structure of the Ni region. Comparisons with recently reported similar effects in reactions induced by the 6He projectile are discussed.

The excitation functions of complete and incomplete fusion reactions of 6Li with Pt nuclei

Experimental results from measuring the energy dependences of cross sections of fusion and transfer reactions for 6Li beams and Pt targets are presented. The experiments were performed using the MSP-144 magnetic analyzer; stacks of platinum foils were installed at the focal plane of this analyzer. In the energy range 22.5–42.5 MeV, the energy resolution of the beam hitting the target stack was not worse than 0.25 MeV and that of the transmitted beam was not worse than 0.40 MeV. The yields of products of neutron and deuteron transfer reaction on target nuclei were measured using the γ activity induced in the platinum targets. Thus, excitation functions for transfer reactions were obtained in a wide energy range, including near the Coulomb barrier. It was shown that the basic reaction channel is the deuteron capture from 6Li. In this case, the maximum of the excitation function for 6Li breakup and subsequent deuteron capture lies near the Coulomb barrier of the reaction.

Neutron transfers at low-energy collisions of nonspherical nuclei

A semiclassical model is used to analyze the evolution of the valence-neutron wave function at a collision between a spherical 48Ca nucleus and a deformed 248Cm nucleus with near-Coulomb-barrier energies. The probabilities of neutron transfers are determined as a function of minimum internuclear distance.

Structure of theN=27isotones derived from theAr44(d,p)Ar45reaction

The $^{44}\mathrm{Ar}$($d,p$)$^{45}\mathrm{Ar}$ neutron transfer reaction was performed at $10A$ MeV. Measured excitation energies, deduced angular momenta, and spectroscopic factors of the states populated in $^{45}\mathrm{Ar}$ are reported. A satisfactory description of these properties is achieved in the shell model framework using a new $\mathit{sdpf}$ interaction. The model analysis is extended to more exotic even-$Z$ nuclei down to ${}_{14}^{41}{\mathrm{Si}}_{27}$ to study how collectivity impacts the low-lying structure of $N=27$ neutron-rich nuclei.

Neutron transfer dynamics and doorway to fusion in time-dependent Hartree-Fock theory

We analyze the details of mass exchange in the vicinity of the Coulomb barrier for heavy-ion collisions involving neutron-rich nuclei using the time-dependent Hartree-Fock (TDHF) theory. We discuss the time-dependence of transfer and show that the potential barriers seen by individual single-particle states can be considerably different than the effective barrier for the two interacting nuclei having a single center-of-mass. For this reason we observe a substantial transfer probability even at energies below the effective barrier.

The role of configurations of neutron halo in the formation of the model vertex function for description of the two-neutron transfer reaction

The nuclear vertex functions for virtual decay of halo nuclei 6He → α + n + n (11Li-9Li + n + n) for dineutron and cigarlike configurations of the neutron halo have been analytically investigated using the diagram method of direct nuclear reactions. These vertex functions describe the one-step process of two-neutron transfer. It is shown that the angular and energy distributions of the reaction products (α particles, 9Li, etc.) in different ranges of variables correspond to different structural elements of the halo. The vertex function describing the two-step process of halo neutron transfer has also been analyzed.

Exotic molecular structures in highly-excited states of 12Be

The generalized two-center cluster model (GTCM), which can treat static structures and dynamical reactions in excited states, is applied to the light neutron-rich system, 12Be = α+α+4N. We discuss the change of the neutrons' configuration around two α-cores from the covalent structure to the ionic one. It is shown that, in the unbound region above particle-decay thresholds, the ionic configurations appear as the molecular resonances of α+8He, 6He+6He and 5He+7He. A new type of superdeformation is possible, and we find here the covalent superdeformation which has a hybrid configuration of the covalent and ionic ones. The excitation of these exotic structures through the two neutron transfer reaction is also discussed.

Neutron transfers and collective excitations at frontal and grazing low-energy collisions of heavy ions

Semi-classical models have been used to investigate the evolution of the wave functions of external neutrons and rotation of a deformed 154Sm nucleus upon collision with a spherical 16O nucleus with energies near the Coulomb barrier. The probabilities of neutron transfers in the 40Ca + 96Zr reaction are determined.

The role of various mechanisms in the formation of the 12B nucleus in the 10B(t, p)12B reaction

The angular distribution of protons from the 10B(t, p)12B reaction is analyzed within the framework of three mechanisms: dineutron cluster stripping, heavy 9Be cluster stripping, and successive time-delay neutron transfer. The dineutron cluster stripping and successive neutron transfer mechanisms are shown to be of considerable importance. Wave functions of the relative motion of the 10B and dineutron, as well as of the 10B and both neutrons, in the 12B ground state are reconstructed, which revealed that the neutron halo in the 12B nucleus practically does not manifest itself in the 10B(t, p)12B reaction.

Neutron transfers and collective excitations at frontal and grazing low-energy collisions of heavy ions

Neutron transfers and collective excitations at frontal and grazing low-energy collisions of heavy ions

Barrier distributions fromS32+Zr90,96quasi-elastic scattering: Investigation of the role of neutron transfer in sub-barrier fusion reactions

The differential cross sections of quasi-elastic scattering at backward angles were measured with high precision for 32 S+ 90,96 Zr around the Coulomb barrier, and barrier distributions were extracted from the measured excitation functions. The experimental barrier distribution of 32 S+ 90 Zr is well reproduced by the coupled-channels calculations including the low-lying quadruple and octupole vibrations in 32 S and 90 Zr. However, the model with the same coupling scheme fails to reproduce the experimental barrier distribution for 32 5+ 96 Zr. The coupled-channels calculation including the neutron transfer channels in the system 32 5 + 96 Zr gives an improved description of the experimental data. A comparison of the data on 40 Ca+ 90,96 Zr shows that the two systems 32 5, 40 Ca+ 90 Zr display barrier distributions that are similar to each other, whereas the barrier distributions of 32 S, 40Ca+ 96 Zr are both wider and flatter than the those of 40 Ca+ 90,96 Zr. The present results strongly indicate that neutron transfer plays an important role in the fusion processes.

Measurements of fusion reactions induced by radioactive 132Sn on 64Ni

Evaporation residue and fission cross sections of radioactive 132Sn on 64Ni were measured. Statistical model calculations using parameters simultaneously fitting stable Sn+64Ni data reproduce the 132Sn induced reaction very well. A large sub-barrier fusion enhancement was observed. The enhancement can be accounted for by coupled-channels calculations including inelastic excitation of the projectile and target, and neutron transfer.

Study of N = 16 for Ne isotopes

27Ne has been investigated through the one neutron transfer reaction 26Ne(d,p)27Ne in inverse kinematics at 9.7 MeV/nucleon. The results support the existence of a low lying negative parity state in 27Ne which is a signature of a reduced sd-fp shell gap in the N = 16 neutron rich region, at variance with stable nuclei.

Study of the structure of neutron halo using neutron transfer reaction

To estimate the probability of two-neutron configurations in halo nuclei, we propose an experimental method of studying neutron-neutron correlations at periphery of such nuclei by measuring two-neutron transfer reaction. The experimental study of 6He + A ↦ 4He + B for various targets is performed using 6He beam of Flerov Laboratory of Nuclear Reactions (JINR, Dubna) at energy of about 15 MeV/u and technique of nuclear photoemulsions. Searching for events of two-nucleon transfer reaction and their processing is performed using the PAVICOM-setup at P.N. Lebedev Physical Institute.

A 3-D multiband closure for radiation and neutron transfer moment models

We derive a 3D multi-band moment model and its associated closure for radiation and neutron transfer. The new closure is analytical and nonlinear but very simple. Its derivation is based on the maximum entropy closure and assumes a Wien shape for the intensity when used in the Eddington tensor. In the multi-band approach, the opacity is re-arranged (binned) according to the opacity value. The multi-band model propagates identically all photons/neutrons having the same opacity. This has been found to be a good approximation on average since the transport is mostly determined by the opacities and less by the frequencies. This same concept is used to derive the closure. We prove on two complex test atmospheres (the solar atmosphere and an artificial atmosphere) that the closure we have derived has good accuracy. All approximations made in deriving the model have been carefully numerically checked and quantified.

Excitation functions for complete fusion and transfer reactions in the interaction of 6He with 197Au nuclei

The excitation functions for the fusion reactions with subsequent neutron evaporation, 197Au(6He, xn)203 − xnTl (x = 2−7), and the neutron transfer reactions with production of the 196Au and 198Au isotopes have been measured. Unusually high cross section of the 198Au isotope production at energies below the Coulomb barrier has been observed. Possible mechanisms of production and decay of the transfer reaction products are considered.

Single neutron transfer coupling effects on sub-barrier elastic scattering and near-barrier fusion ofC15

To date, the possible effects of coupling to nucleon transfer reactions on the elastic scattering and fusion of weakly bound exotic nuclei have been largely neglected. The $^{15}\mathrm{C}$ nucleus presents a virtually unique opportunity to test these effects for an almost pure s${}_{1/2}$ single neutron halo nucleus. We present a series of coupled reaction channel calculations of the sub-barrier elastic scattering and single neutron transfer reactions, plus near-barrier excitation functions of the total fusion cross section for the $^{12}\mathrm{C}$, $^{13}\mathrm{C}$, and $^{15}\mathrm{C}+^{208}\mathrm{Pb}$ systems. The method is validated against data for $^{12}\mathrm{C}$ and $^{13}\mathrm{C}+^{208}\mathrm{Pb}$. A large effect on the sub-barrier elastic scattering due to coupling to the ($^{15}\mathrm{C}$,$^{14}\mathrm{C}$) single neutron stripping reaction is found, ascribed to the 2s${}_{1/2}$ halo nature of the $^{15}\mathrm{C}$ ground state, in contrast to the two stable carbon isotopes. We also find a significant diminution of the above barrier total fusion cross section for $^{15}\mathrm{C}$ due to this coupling, again in contrast to the stable isotopes.

Fusion of radioactiveSn132withNi64

Evaporation residue and fission cross sections of radioactive $^{132}\mathrm{Sn}$ on $^{64}\mathrm{Ni}$ were measured near the Coulomb barrier. A large subbarrier fusion enhancement was observed. Coupled-channel calculations, including inelastic excitation of the projectile and target, and neutron transfer are in good agreement with the measured fusion excitation function. When the change in nuclear size and shift in barrier height are accounted for, there is no extra fusion enhancement in $^{132}\mathrm{Sn}$+$^{64}\mathrm{Ni}$ with respect to stable Sn+$^{64}\mathrm{Ni}$. A systematic comparison of evaporation residue cross sections for the fusion of even $^{112\ensuremath{-}124}\mathrm{Sn}$ and $^{132}\mathrm{Sn}$ with $^{64}\mathrm{Ni}$ is presented.