Pickup Reactions Research Articles

Experimental study ofAl26through the1npick-up reactionAl27(d,t)

The $^{27}\mathrm{Al}(d,t)$ reaction has been studied to extract spectroscopic information for the odd-odd nucleus $^{26}\mathrm{Al}$. The excited states of $^{26}\mathrm{Al}$ up to 5.50 MeV have been analyzed using the local, zero range distorted wave Born approximation. A new set of optical model potential parameters was extracted from the measured elastic scattering angular distribution. The spectroscopic factors calculated for these states are found to be in good agreement with previously reported values for the same; they are also in agreement with those obtained from shell model predictions.

Dipole resonance splitting and shell structure peculiarities of 52Cr nucleus

A microscopic description of dipole resonances in the 52Cr nucleus is presented using the multi-particle shell model (MSM) and direct pick-up reaction data. The obtained form factors and effective cross sections are compared to the experimental data on photoneutron and photoproton disintegration channels.

Single-particle strength in neutron-rich 71Cu from the (d,3He) proton pick-up reaction

We have measured the 72Zn(d,3He)71Cu proton pick-up reaction in inverse kinematics at 38 MeV/u. A dedicated set-up was developed to overcome the experimental challenges posed by the low cross section of the reaction and the low energy of the outgoing 3He particles. The excitation-energy spectrum was reconstructed and spectroscopic factors were obtained after analysis of the angular distributions in the finite-range Distorted-Wave Born Approximation (DWBA). The results show that unlike for the πf5/2 orbital, the πf7/2 singleparticle strength is not appreciably affected by the addition of neutrons beyond N = 40.

Current understanding of the reaction mechanism in two-nucleon transfer reactions

The current understanding of the reaction mechanism of proton-induced two- nucleon transfer reactions is reviewed. The ideal is to employ a theoretical formulation which accurately reflects the important physics, but which is nevertheless still fairly simple. The influence of sequential transfer of the two nucleons involved in a pickup reaction is the most obvious complication that has to be considered. This is discussed in detail.

Transition from collectivity to single-particle degrees of freedom from magnetic moment measurements on 3882Sr 44 and 3890Sr 52

The evolution of shell structure and the fragility of the benchmark magic numbers is a topic of major interest in nuclear-structure physics. The authors measured the structure-sensitive $g$ factors of states in unstable even-even strontium isotopes, following $\ensuremath{\alpha}$-pickup reactions by krypton beams from a carbon target. The results help elucidate how protons and neutrons contribute to the evolution of nuclear structure in this important mass region where rapid structural changes occur.

Structure of dipole resonances in iron isotopes 54Fe and 56Fe

The probability distributions of photoexcitations in 54Fe and 56Fe nuclei were obtained within the particle-core coupling version of the multiparticle shell model by using the spectroscopy of direct pickup reactions.

Study of the multi-nucleon transfer reactions of136Xe +198Pt for producing exotic heavy nuclei

The feasibility of the multi-nucleon transfer (MNT) reaction in the 136 Xe + 198 Pt system was investigated for synthesizing neutron-rich heavy nuclei around mass number A 200 of astrophysical interest. Identification of the projectile-like fragments (PLF's) was successfully performed by using VAMOS++ spectrometer. The isotopic distributions of the PLF's produced by two-proton stripping and pickup reactions were compared with each other, demonstrating the properties of the MNT reactions observed in the present system. The two-proton pickup channels strongly populated than the two- proton stripping channels were observed. The isotopic distributions for di erent total kinetic energy loss (TKEL) ranges are also discussed. The overall enhancement of the strength of the two-proton pickup compared with the two-proton stripping appears to be related to the MNT reactions with relatively moderate energy dissipation.

Study of neutron-neutron interaction in proton pick-up reactions on3H

The study of neutron-neutron interaction is performed in the reaction of proton pick-up from the triton d+ 3 H 3 He+n+n. The experiment will be carried out in the geometry of final state interaction measuring the relative energy of two neutrons. The simulation of the reaction showed the possibility of determining with good accuracy the energy of quasi-bound nn-singlet state, which is the main characteristic of nn-interaction. The test of the experimental technique was performed in the d+d 2 He+n+n reaction at the deuteron beam of U-120 cyclotron of Skobeltsyn Institute of Nuclear Physics.

Nuclear structure and reaction studies with exotic nuclei at the FRS-ESR

Nuclear physics with exotic nuclei in storage rings was pioneered at the SIS-ESR facility in combination with the fragment separator FRS. Already the first experiments in the early 1990s gave access to ground-state properties like masses and half-lives and indicated the research potential of this novel instrumental approach. Many new data have been obtained and interesting phenomena have been explored, e.g. the mass surface was mapped over large areas of the chart of nuclei, isomer studies of long-lived states (with half-lives of the order minutes) became possible, the modification of decay properties for highly-charged, high-Z exotic nuclei was observed, and new decay modes, like the beta-decay to bound final states, were studied for the first time. A few years ago, direct reaction experiments on internal targets using inverse kinematics were started: transfer and pickup reactions of astrophysical interest were performed with stable isotopes at energies approaching the Gamow-window, while elastic and inelastic scattering experiments were performed with secondary beams of the unstable doubly magic isotope 56Ni quite recently. In this contribution, the achievements will be reviewed and recent results will be presented. It is dedicated to Paul Kienle.

Experimental64Zn(d⃗,t)63Zn spectroscopic factors: Guidance for isospin-symmetry-breaking calculations

With the recent inclusion of core orbitals to the radial-overlap component of the isospin-symmetry-breaking (ISB) corrections for superallowed Fermi $\ensuremath{\beta}$ decay, experimental data are needed to test the validity of the theoretical model. This work reports measurements of single-neutron pickup reaction spectroscopic factors into ${}^{63}$Zn, one neutron away from ${}^{62}$Zn, the superallowed daughter of ${}^{62}$Ga. The experiment was performed using a 22-MeV polarized deuteron beam, a Q3D magnetic spectrograph, and a cathode-strip focal-plane detector to analyze outgoing tritons at nine angles between ${10}^{\ensuremath{\circ}}$ and ${60}^{\ensuremath{\circ}}$. Angular distributions and vector analyzing powers were obtained for all 162 observed states in ${}^{63}$Zn, including 125 newly observed levels, up to an excitation energy of 4.8 MeV. Spectroscopic factors are extracted and compared to several shell-model predictions, and implications for the ISB calculations are discussed.

Limited asymmetry dependence of correlations from single nucleon transfer.

Single nucleon pickup reactions were performed with a 18.1 MeV/nucleon (14)O beam on a deuterium target. Within the coupled reaction channel framework, the measured cross sections were compared to theoretical predictions and analyzed using both phenomenological and microscopic overlap functions. The missing strength due to correlations does not show significant dependence on the nucleon separation energy asymmetry over a wide range of 37 MeV, in contrast with nucleon removal data analyzed within the sudden-eikonal formalism.

Study of 0+States at iThemba LABS

An initial series of experiments utilising the (3 He,n) reactions have been carried out at iThemba LABS. These are complimentary to transfer reactions such as (t,p) stripping or (p,t) pick-up reactions measurements using magnetic spectrometers. However, in the past, (3 He,n) measurements have suffered from ambiguities due to the low energy resolution inbuilt into the time-of-flight techniques used. By combining neutron detection techniques with the AFRODITE γ -ray array, it has been shown that very good energy resolutions can be achieved. This enables the relative strengths of two proton stripping to excited states, separated by only a few keV, to be accurately measured. This technique has been applied to first excited 02 + states and, in particular to those uniquely seen in double β -decay.

Momentum dependence of spin polarization for beta emitting nuclei produced through charge exchange reaction at intermediate energy

In order to investigate the polarization process in charge exchange reactions, we observed the momentum and angular distribution as well as the nuclear polarization of a proton-rich beta-emitting nucleus, 28P (I π = 3 + , T1/2 = 270 msec), produced through the reaction 28Si+ 9Be at E = 100 MeV/u, by selecting the momentum and the ejection angle. An analysis by using double Gaussian functions resolved the observed momentum distribution into two reaction components, nucleon knockout and pick-up abrasion reactions, as suggested in a previous study. The behavior of the observed angular distribution and nuclear polarization implies the influence of those two components. The momentum dependence of the observed nuclear polarization of 28P could be consistently reproduced by a simple model, in which two reaction components are considered. The present study also shows that the charge exchange reaction at intermediate energy is a useful method to produce polarized beta-emitting nuclei, especially for proton-rich nuclei.

Probing the states of nucleons in exotic nuclei

Many of the most exotic neutron-proton asymmetric nuclei are produced in relatively small numbers in high-energy fragmentation reactions. They are produced as fast secondary beams with energies of 100 MeV per nucleon or more. Developments made and recent results that both exploit and assess fast one- and two-nucleon removal reactions from such secondary beams are reviewed. This includes very recent work that interfaces the sudden, eikonal reaction models used with more ab-initio nuclear structure inputs. The potential use of neutron pick-up reactions to study particle-like states in exotic nuclei is also outlined.

Measurement and model analysis of(n,xα)cross sections for Cr, Fe,59Co, and58,60Ni from threshold energy to 150 MeV

Neutron reactions that produce $\ensuremath{\alpha}$ particles have been investigated experimentally and analyzed by reaction model calculations for incident neutron energies from threshold to 150 MeV on elemental chromium and iron. The cross sections were measured at the Los Alamos Neutron Science Center by direct observation of $\ensuremath{\alpha}$ particles. Previous data on isotopes ${}^{59}$Co and ${}^{58,60}$Ni were also included in the analysis. The model calculations are made for both statistical decay and pre-equilibrium processes. This study particularly focuses on the pre-equilibrium cluster emission, which is described by the clustering exciton model of Iwamoto and Harada. We calculate the $\ensuremath{\alpha}$-particle formation factors numerically without any of the approximations that appeared in the original model. The model parameter $\ensuremath{\Delta}R$, the nuclear surface area where the pickup reaction may occur, is determined by fitting the calculated $\ensuremath{\alpha}$-particle energy spectra to experimental data. The calculated $\ensuremath{\alpha}$-particle-production cross sections agree well with the measured data, except for the Cr case. With a simple sensitivity study for the level density parameters, it is reported that relatively small changes in the level density parameters improve the reproduction of experimental data significantly. Our realistic model calculations for the pre-equilibrium process shed light on uncertainties in the nuclear level densities in statistical decay calculation.

Intermediate-energy inverse-kinematics one-proton pickup reactions on neutron-deficientfp-shell nuclei

Background: Thick-target-induced nucleon-adding transfer reactions onto energetic rare-isotope beams are an emerging spectroscopic tool. Their sensitivity to single-particle structure complements one-nucleon removal reaction capabilities in the quest to reveal the evolution of nuclear shell structure in very exotic nuclei. Purpose: To add intermediate-energy, carbon-target-induced one-proton pickup reactions to the arsenal of $\gamma$-ray tagged direct reactions applicable in the regime of low beam intensities and to apply these for the first time to $fp$-shell nuclei. Methods: Inclusive and partial cross sections were measured for the $\nuc{12}{C}(\nuc{48}{Cr},\nuc{49}{Mn}+\gamma)$X and $\nuc{12}{C}(\nuc{50}{Fe},\nuc{51}{Co}+\gamma)$X proton pickup reactions at 56.7 and 61.2 MeV/nucleon, respectively, using coincident particle-$\gamma$ spectroscopy at the NSCL. The results are compared to reaction theory calculations using $fp$-shell-model nuclear structure input. For comparison with our previous work, the same reactions were measured on \nuc{9}{Be} targets. Results: The measured partial cross sections confirm the specific population pattern predicted by theory, with pickup into high-$\ell$ orbitals being strongly favored; driven by linear and angular momentum matching. Conclusion: Carbon target-induced pickup reactions are well-suited, in the regime of modest beam intensity, to study the evolution of nuclear structure, with specific sensitivities that are well described by theory.

Origins of dipole resonance strength fragmentation in calcium and titanium isotopes

Theoretical description of dipole resonances in 46 Ti, 48 Ti, 50 Ti, 48 Ca, 40 Ca was performed. The distribution of the “hole” among the states of final nuclei was taken into account using information on pick-up reactions. The obtained results are in reasonable agreement with experimental data.

Incident-energy dependence of the analyzing power in the58Ni(p,3He)56Co reaction between 80 and 120 MeV

This project looks at the angular distributions of the differential cross sections and analyzing powers of a few low lying states of 56 Co in the reaction 58 Ni(p, 3 He) 56 Co at three different incident energies between 80 and 120 MeV. The measurements are compared with zero-range distorted-wave Born approximation (DWBA) calculations in which we assume a simple direct two-nucleon pickup process. Earlier inclusive (p, 3 He) reaction studies on similar targets were successfully treated in terms of a statistical pre-equilibrium multistep formalism, in which the final stage of the reaction involved a deuteron pickup, described by means of the DWBA. The analyzing power was shown to be rather sensitive to the contributions of the different order steps. However some features observed in the analyzing powers of these inclusive studies, though reproduced by the theory, are not fully understood. We therefore investigate the ability of the DWBA model to describe the (p, 3 He) pickup reaction to discrete states at different incident energies using a high resolution spectrometer.

Formation of heavy-meson bound states by two-nucleon pick-up reactions

We develop a model to evaluate the formation rate of the heavy mesic nuclei in the two nucleon pick-up reactions, and apply it to the $^6$Li target cases for the formation of heavy meson-$\alpha$ bound states, as examples. The existence of the quasi-deuteron in the target nucleus is assumed in this model. It is found that the mesic nuclei formation in the recoilless kinematics is possible even for heavier mesons than nucleon in the two nucleon pick-up reactions. We find the formation rate of the meson-$\alpha$ bound states can be around half of the elementary cross sections at the recoilless kinematics with small distortions.

Microscopic description of E1 resonance in 48Ca

The cross sections of photoneutron and photoproton disintegration of the 48Ca nucleus are obtained on the basis of the particle-core coupling version of the multiparticle shell model using the spectroscopy data on direct pickup reactions.