Neutron Transfer Research Articles

Multi-neutron transfer coupling in sub-barrier32S +90,96Zr fusion reactions

The role of neutron transfers is investigated in the fusion process below the Coulomb barrier by analyzing 32S+90Zr and 32S+96Zr as benchmark reactions. A full coupled-channel calculation of the fusion excitation functions has been performed for both systems by using multi-neutron transfer coupling for the more neutron-rich reaction. The enhancement of fusion cross sections for 32S+96Zr is well reproduced at sub-barrier energies by NTFus code calculations including the coupling of the neutron-transfer channels following the Zagrebaev semiclassical model. We found similar effects for 40Ca+90Zr and 40Ca+96Zr fusion excitation functions.

Fusion of60Ni +100Mo below barrier

The fusion cross section of 60 Ni + 100 Mo has been measured down to microbarn level, looking for hindrance at low energy, in a system with positive Q-values for neutron transfer. The measured cross sections look similar to those of the nearby 64 Ni + 100 Mo, but no conclusive statement can be made at this stage, as to the onset of hindrance in this system.

Study of fusion in6,7Li+197Au at near barrier energies

Excitation functions are measured for complete fusion and transfer reactions of 6 Li and 7 Li with 197 Au at energies around the Coulomb barrier. Coupled channel calculations including the couplings to both target and projectile excited states have been performed and are found to explain the data at energies below the barrier. At above barrier energies the complete fusion cross sections are found to be suppressed compared to the coupled channel calculations for both the systems. A systematic comparison of fusion cross-section for halo nuclei 6,8 He and weakly bound stable nuclei 6,7 Li on 197 Au target is also presented. Large neutron transfer cross-sections are observed for 6,7 Li as compared to tightly bound projectiles 12 C, 16 O.

Discovery of the Shape Coexisting0+State inMg32by a Two Neutron Transfer Reaction

The "island of inversion" nucleus 32 Mg has been studied by a (t, p) two neutron transfer reaction in inverse kinematics at REX-ISOLDE. The shape coexistent excited 0+ state in 32 Mg has been identified by the characteristic angular distribution of the protons of the Δ L=0 transfer. The excitation energy of 1058 keV is much lower than predicted by any theoretical model. The low γ-ray intensity observed for the decay of this 0+ state indicates a lifetime of more than 10 ns. Deduced spectroscopic amplitudes are compared with occupation numbers from shell-model calculations.

Математическое моделирование нейтронных передач в ядерных реакциях с учетом спин-орбитального взаимодействия

Математическое моделирование нейтронных передач в ядерных реакциях с учетом спин-орбитального взаимодействия

Near-barrier fusion ofS32+Zr90,96: The effect of multi-neutron transfers in sub-barrier fusion reactions

Fusion excitation functions have been measured for the first time with rather good accuracy for $^{32}\mathrm{S}+^{90}\mathrm{Zr}$ and $^{32}\mathrm{S}+^{96}\mathrm{Zr}$ near and below the Coulomb barrier. The sub-barrier cross sections for $^{32}\mathrm{S}+^{96}\mathrm{Zr}$ are much larger than for $^{32}\mathrm{S}+^{90}\mathrm{Zr}$. A coupled-channels calculation considering the inelastic excitations is capable of describing sub-barrier enhancement only for $^{32}\mathrm{S}+^{90}\mathrm{Zr}$. The unexplained part for $^{32}\mathrm{S}+^{96}\mathrm{Zr}$ is found to be correlated with the positive-$Q$-value intermediate neutron transfers in this system. The comparison with $^{40}\mathrm{Ca}+^{96}\mathrm{Zr}$ suggests that couplings to the positive-$Q$-value neutron transfer channels may play a role in the sub-barrier fusion enhancement. Multi-neutron transfers are taken into account in Zagrebaev's semiclassical model to explain the discrepancies of the sub-barrier fusion cross sections for $^{32}\mathrm{S}+^{96}\mathrm{Zr}$.

Reactions with the double-Borromean nucleusHe8

Differential cross sections for elastic-scattering and neutron-transfer reactions along with cross sections for fusion in the $^{8}\mathrm{He}$$+$$^{65}\mathrm{Cu}$ system are reported at energies above the Coulomb barrier (${E}_{\mathrm{lab}}=$ $19.9$ and $30.6$ MeV). The present work demonstrates the feasibility of using inclusive measurements of characteristic in-beam $\ensuremath{\gamma}$ rays with low-intensity ($~$$10$${}^{5}$ pps) radioactive ion beams to obtain the residue cross sections for fusion and neutron transfer. Exclusive measurements of $\ensuremath{\gamma}$ rays in coincidence with light charged particles have been used to further characterize the direct reactions induced by this double-Borromean nucleus. Coupled reaction channels calculations are used to illustrate the important role played by the transfer channels and to help in understanding the influence of the structure of $^{8}\mathrm{He}$ on the reaction mechanism.

α-particle production inHe6+Sn120collisions

The collision $^{6}\mathrm{He}+^{120}\mathrm{Sn}$ has been investigated at four energies near the Coulomb barrier. A large yield of $\ensuremath{\alpha}$ particles has been detected, with energies around the energy of the scattered $^{6}\mathrm{He}$ beam. The energy and angular distributions of the $\ensuremath{\alpha}$ particles have been analyzed and compared with breakup and neutron transfer calculations.

Surface-enhanced pair transfer amplitude in quadrupole states of neutron-rich Sn isotopes

We investigate the neutron pair transfer modes associated with the low-lying quadrupole states in neutron-rich Sn isotopes by means of the quasiparticle random phase approximation based on the Skyrme-Hartree-Fock-Bogoliubov mean field model. The transition strength of the quadrupole pair-addition mode feeding the $2_1^+$ state is enhanced in the Sn isotopes with $A \geq 132$. The transition density of the pair-addition mode has a large spatial extension in the exterior of nucleus, reaching far to $r\sim 12-13$ fm. The quadrupole pair-addition mode reflects sensitively a possible increase of the effective pairing interaction strength in the surface and exterior regions of neutron-rich nuclei.

Single-particle structure of neutron-rich nuclei

Neutron transfer (d,p) reactions have been measured with rare isotope beams of 132Sn, 130Sn and 134Te accelerated to ≈4.5 MeV/u interacting with CD2 targets. Reaction protons were detected in an early implementation of the ORRUBA array of position-sensitive silicon strip detectors. Neutron excitations in the 2f7/2, 3p3/2, 3p1/2 and 2f5/2 orbitals were populated.

Migration of Nuclear Shell Gaps Studied in thed(Ne24,pγ)Ne25Reaction

The transfer of neutrons onto 24Ne has been measured using a reaccelerated radioactive beam of 24Ne to study the (d,p) reaction in inverse kinematics. The unusual raising of the first 3/2+ level in 25Ne and its significance in terms of the migration of the neutron magic number from N=20 to N=16 is put on a firm footing by confirmation of this state's identity. The raised 3/2+ level is observed simultaneously with the intruder negative parity 7/2- and 3/2- levels, providing evidence for the reduction in the N=20 gap. The coincident gamma-ray decays allowed the assignment of spins as well as the transferred orbital angular momentum. The excitation energy of the 3/2+ state shows that the established USD shell model breaks down well within the sd model space and requires a revised treatment of the proton-neutron monopole interaction.

Consideration of the spin-orbit interaction in the description of nucleon transfers upon heavy ionic nuclei collisions

A difference scheme is proposed for the numerical solution of a time-dependent Schrodinger equation with spin-orbit interaction. Evolution of an external neutron wave function with the minimum full moment projection onto the internuclear axis and the probability of neutron transfer upon frontal collisions of 40Ca and 96Zr nuclei are calculated.

Neutron-Proton Asymmetry Dependence of Spectroscopic Factors in Ar Isotopes

Spectroscopic factors have been extracted for proton-rich 34Ar and neutron-rich 46Ar using the (p, d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton-rich nucleus 34Ar compared to that of 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements.

Geometric classification of nucleon transfer at moderate low-energies

Nucleon transfer is studied with a focus on charge equilibration. It is completely classified into six types. The preferred nucleon transfer (i.e. neutron transfer, proton transfer, dual-way transfer, etc.) is predictable based on this classification, which is verified within the framework of microscopic time-dependent density functional calculations. This classification gives a simple explanation for the reason why the proton-richness does not necessarily result in the enhancement of proton transfer contrary to the neutron-richness in neutron transfer.

Investigation of deep inelastic reactions in 238U + 238U at Coulomb barrier energies

We investigated deep inelastic reactions in 238U + 238U collisions at 6.09, 6.49, 6.91, 7.1 and 7.35×A MeV at the VAMOS spectrometer (GANIL). A large transfer of neutrons and protons was observed at all beam energies. For a transfer of more than 10 nucleons the total kinetic energy of the detected fragments becomes independent of the beam energy and reaches values far below the Coulomb barrier for spherical fragments. This points to the formation of a di-nuclear system in the entrance channel which develops an elongated shape and a strong neck. For such reactions we expect an enhanced lifetime of the di-nuclear system which is significantly longer than the time scale for elastic and quasi-elastic reactions. Different theoretical approaches predict delay times of more than 5×10-21 s for a subset of our data.

Neutron single-particle states above theN=164subshell in98251Cfand96249Cmstudied by neutron transfer reactions

Single-particle state assignments in $^{251}\mathrm{Cf}$ and $^{249}\mathrm{Cm}$ at $~1$ MeV excitation have been deduced from cross sections previously measured for the $^{250}\mathrm{Cf}(d,p)^{251}\mathrm{Cf}$ and $^{248}\mathrm{Cm}(^{4}\mathrm{He},^{3}\mathrm{He})^{249}\mathrm{Cm}$ reactions. The assignments are supported by observed cross-section signatures and intraband level spacings. The observed energies of these single-particle states, after pairing effects are removed, are in good agreement with values calculated using a Woods-Saxon single-particle potential. Neutron level diagrams, showing level spacings as a function of ${\ensuremath{\nu}}_{2},{\ensuremath{\nu}}_{4},$ and ${\ensuremath{\nu}}_{6}$, are extended to include neutron orbitals above $N=164$.

Modern Rutherford Experiment: Tunneling of the Most Neutron-Rich Nucleus

A modern variation of the Rutherford experiment to probe the tunneling of exotic nuclear matter from the measurement of the residues formed in the bombardment of (197)Au by extremely neutron-rich (8)He nuclei is presented. Using a novel off-beam technique the most precise and accurate measurements of fusion and neutron transfer involving reaccelerated unstable beams are reported. The results show unusual behavior of the tunneling of (8)He compared to that for lighter helium isotopes, highlighting the role of the intrinsic structure of composite many-body quantum systems and pairing correlations.

Dynamical deformation of nuclei in deep-inelastic collisions: A gamma coincidence study of 130Te + 275 MeV 64Ni and 208Pb + 345 MeV 58Ni heavy ion reactions

Products of 130Te + 275 MeV 64Ni and 208Pb + 345 MeV 58Ni collisions at energies slightly above the Coulomb barrier have been studied in two gamma spectroscopy thick target experiments. The product yield distributions have been established from the γ – γ coincidence analysis supplemented by target radioactivity measurements. Neutron evaporation from excited primary products has been estimated to determine the pre-emission maps of fragments. The transfer of protons and neutrons between the colliding ions is discussed in terms of the N / Z ratio equilibration. The discussion of experimental N / Z values compared with expectations based on potential energy minimizations leads to conclusion that the involved nuclei are dynamically deformed during the crucial interaction time. These results are discussed in connection with the earlier published study of the 208Pb + 350 MeV 64Ni system [1]. The present and perspective use of deep-inelastic reactions for spectroscopic studies of exotic neutron-rich nuclei in experiments with stable and radioactive beams is outlined.

8Li optical potential from 7Li( 18O, 17O) 8Li reaction analysis

Angular distributions for the 7Li( 18O, 17O) 8Li reaction were measured for the transitions to the ground and excited states of 8Li and 17O at the energy E lab ( O 18 ) = 114 MeV . The data were analyzed with coupled-reaction-channels method for one- and two-step transfers of nucleons and clusters. In the analysis, the Li 7 + O 18 potential deduced in the analysis of the elastic Li 7 + O 18 -scattering data as well as shell-model spectroscopic amplitudes of transferred nucleons and clusters were used. The deduced Li 8 + O 17 optical potential needed to describe the ground state transfer has a weaker imaginary potential than that of the previously deduced 7Li potential but a very similar real one. The data are well described assuming a single neutron transfer over the complete angular range.

Special features of nuclear reactions induced by loosely bound 6He and 6,7Li nuclei in the vicinity of the Coulomb barrier height

Excitation functions are measured for complete-fusion and transfer reactions induced by the interaction of 6He and 6Li with 206Pb, 209Bi, and Pt. Data obtained for fusion reactions induced by 6He ions deviate from the predictions of the statistical model of compound-nucleus decay at projectile energies in the vicinity of the Coulomb barrier height. A strong enhancement of cross sections for fusion reactions induced by the interaction of 6He with target nuclei is observed. The cross sections for reactions of cluster transfer, neutron transfer from 6He, and deuteron transfer from 6Li at deep-subbarrier energies are also found to be enhanced. These results are discussed from the point of view of the effect of the cluster structure of nuclei on the interaction probability at energies in the vicinity of the Coulomb barrier height.