Beams In Inverse Kinematics Research Articles

Three-body optical potentials in (d,p) reactions and their influence on indirect study of stellar nucleosynthesis

Model uncertainties arising due to suppression of target excitations in the description of deuteron scattering and resulting in a modification of the two-body interactions in a three-body system are investigated for several $(d,p)$ reactions serving as indirect tools for studying the astrophysical $(p,\ensuremath{\gamma})$ reactions relevant to $rp$ process. The three-body nature of the deuteron-target potential is treated within the adiabatic distorted-wave approximation (ADWA) which relies on a dominant contribution from the components of the three-body deuteron-target wave function with small $n\text{\ensuremath{-}}p$ separations. This results in a simple prescription for treating the explicit energy dependence of two-body optical potentials in a three-body system requiring nucleon optical potentials to be evaluated at a shifted energy with respect to the standard value of half the deuteron incident energy. In addition, the ADWA allows for leading-order multiple-scattering effects to be estimated, which leads to a simple renormalization of the adiabatic potential's imaginary part by a factor of two. These effects are assessed using both nonlocal and local optical potential systematics for $^{26}\mathrm{Al}$, $^{30}\mathrm{P}$, $^{34}\mathrm{Cl}$, and $^{56}\mathrm{Ni}$ targets at a deuteron incident energy of 12 MeV, which is typical for experiments with radioactive beams in inverse kinematics. The model uncertainties induced by the three-body nature of deuteron-target scattering are found to be within $40%$ both in the main peak of angular distributions and in total $(d,p)$ cross sections. At higher deuteron energies, around 60 MeV, model uncertainties can reach 100% in the total cross sections. A few examples of application to astrophysically interesting proton resonances in $^{27}\mathrm{Si}$ and $^{57}\mathrm{Cu}$ obtained using $(d,p)$ reactions and mirror symmetry are given.

A High-Precision Tracking Algorithm for Mass Reconstruction of Heavy-Ion Fragments in the R3B Experiment at FAIR

The multi-purpose R3B (Reactions with Relativistic Radioactive Beams) setup at the future FAIR facility in Darmstadt will be used for various experiments with exotic beams in inverse kinematics. In front and after the reaction target a combination of detectors serves for particle identification and momentum measurements. In order to perform a high-precision charge identification of heavy-ion fragments and achieve a momentum resolution of 10-3 following is required: a time of flight (ToF) measurement with up to 15 ps accuracy, position determination on the order of less than 0.5 mm and a dedicated algorithm for the heavy-ion tracking in highly non-homogeneous dipole field. With these constraints a tracking package is being developed and tested within the R3B software framework, this package has to go into production in fall of 2018. An iterative approach has been chosen for simultaneous track finding and fitting. The design and concept of the package are introduced in this paper, also the tests and the resolution measured with simulated data are presented.

Quasifree ( p,pN ) scattering of light neutron-rich nuclei near N=14

Background: For many years, quasifree scattering reactions in direct kinematics have been extensively used to study the structure of stable nuclei, demonstrating the potential of this approach. The (RB)-B-3 collaboration has performed a pilot experiment to study quasifree scattering reactions in inverse kinematics for a stable C-12 beam. The results from that experiment constitute the first quasifree scattering results in inverse and complete kinematics. This technique has lately been extended to exotic beams to investigate the evolution of shell structure, which has attracted much interest due to changes in shell structure if the number of protons or neutrons is varied. Purpose: In this work we investigate for the first time the quasifree scattering reactions (p, pn) and (p, 2p) simultaneously for the same projectile in inverse and complete kinematics for radioactive beams with the aim to study the evolution of single-particle properties from N = 14 to N = 15. Method: The structure of the projectiles O-23, O-22, and N-21 has been studied simultaneously via (p, pn) and (p, 2p) quasifree knockout reactions in complete inverse kinematics, allowing the investigation of proton and neutron structure at the same time. The experimental data were collected at the (RB)-B-3-LAND setup at GSI at beam energies of around 400 MeV/u. Two key observables have been studied to shed light on the structure of those nuclei: the inclusive cross sections and the corresponding momentum distributions. Conclusions: The knockout reactions (p, pn) and (p, 2p) with radioactive beams in inverse kinematics have provided important and complementary information for the study of shell evolution and structure. For the (p, pn) channels, indications of a change in the structure of these nuclei moving from N = 14 to N = 15 have been observed, i.e., from the 0d(5/2) shell to the 1s(1/2). This supports previous observations of a subshell closure at N = 14 for neutron-rich oxygen isotopes and its weakening for the nitrogen isotopes.

RESONEUT: A detector system for spectroscopy with (d,n) reactions in inverse kinematics

The resoneut detector setup is described, which was developed for resonance spectroscopy using (d,n) reactions with radioactive beams in inverse kinematics and at energies around the Coulomb barrier. The goal of experiments with this setup is to determine the spectrum and proton-transfer strengths of the low-lying resonances, which have an impact on astrophysical reaction rates. The setup is optimized for l=0 proton transfers in inverse kinematics, for which most neutrons are emitted at backward angles with energies in the 80–300 keV range. The detector system is comprised of 9 p-terphenyl scintillators as neutron detectors, two annular silicon-strip detectors for light charged particles, one position-resolving gas ionization chamber for heavy ion detection, and a barrel of NaI-detectors for the detection of γ-rays. The detector commissioning and performance characteristics are described with an emphasis on the neutron-detector components.

Collective 2+ 1 excitations in 206Po and 208,210Rn

In the present study, $B(E2; 2^{+}_{1}\rightarrow 0^{+}_{1})$ values have been measured in the 208,210Rn and 206Po nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics at CERN-ISOLDE. These nuclei have been proposed to lie in, or at the boundary of the region where the seniority scheme should persist. However, contributions from collective excitations are likely to be present when moving away from the N=126 closed shell. Such an effect is confirmed by the observed increased collectivity of the $2^{+}_{1}\rightarrow 0^{+}_{1}$ transitions. Experimental results have been interpreted with the aid of theoretical studies carried out within the BCS-based QRPA framework.

First measurement of isoscalar giant resonances in a stored-beam experiment

Abstract A new technique developed for measuring nuclear reactions at low momentum transfer with stored beams in inverse kinematics was successfully used to study isoscalar giant resonances. The experiment was carried out at the experimental heavy-ion storage ring (ESR) at the GSI facility using a stored 58 Ni beam at 100 MeV/u and an internal helium gas-jet target. In these measurements, inelastically scattered α -recoils at very forward center-of-mass angles ( θ cm ≤ 1.5 ° ) were detected with a dedicated setup, including ultra-high vacuum compatible detectors. Experimental results indicate a dominant contribution of the isoscalar giant monopole resonance at this very forward angular range. It was found that the monopole contribution exhausts 79 − 11 + 12 % of the energy-weighted sum rule (EWSR), which agrees with measurements performed in normal kinematics. This opens up the opportunity to investigate the giant resonances in a large domain of unstable and exotic nuclei in the near future. It is a fundamental milestone towards new nuclear reaction studies with stored ion beams.

The EXL project, recent results and future perspectives

The investigation of light-ion induced reactions with exotic beams in inverse kinematics gives access to a broad range of nuclear structure information in the region far off stability. The future FAIR facility, currently under construction at Darmstadt, will provide new opportunities for studying exotic nuclei. The physics program of the EXL project planned as a part of NUclear STructure, Astrophysics and Reactions at FAIR is outlined. It is proposed as a universal high-precision detector setup surrounding the internal target of the storage ring accompanied by a heavy-ion tagging ring detector and a detector for fast protons and neutrons. Possible realization of the setup is briefly discussed. Earlier feasibility studies with stable stored beams and intensive R&D towards the detectors capable of working in ultra-high vacuum conditions helped preparing the final design of the experimental setup. Results of scattering experiments with the stable ions and a very first reaction experiment performed with radioactive ions in the experimental storage ring (ESR) are presented. Future perspectives of the EXL project with a prototype-setup at the ESR and a possible larger-scale setup are also described.

Cluster-transfer reactions with radioactive beams: A spectroscopic tool for neutron-rich nuclei

AnexploratoryexperimentperformedatREX-ISOLDEtoinvestigatecluster-transferreactionswithradioactive beams in inverse kinematics is presented. The aim of the experiment was to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The reactions 7 Li( 98 Rb,αxn) and 7 Li( 98 Rb,txn) were studied through particle-γ coincidence measurements, and the results are presented in terms of the observed excitation energies and spins. Moreover, the reaction mechanism is qualitatively discussed as a transfer of a clusterlike particle within a distorted-wave Born approximation framework. The results indicate that cluster-transfer reactions can be described well as a direct process and that they can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins.

MINOS: A vertex tracker coupled to a thick liquid-hydrogen target for in-beam spectroscopy of exotic nuclei

MINOS is a new apparatus dedicated to in-beam nuclear structure experiments with low-intensity exotic beams in inverse kinematics at intermediate energies above 150MeV/nucleon. The device is composed of a thick liquid-hydrogen target coupled to a compact time projection chamber (TPC) serving as a vertex tracker. Either used for in-beam gamma spectroscopy of bound excited states or invariant-mass spectroscopy of unbound states, MINOS aims at improving the luminosity by a very significant factor compared to standard solid-target material experiments while improving experimental resolutions.

Magnetic moments of 21+states in124,126,128Sn

The $g$ factors of the first-excited states of stable ${}^{124}$Sn and radioactive ${}^{126,128}$Sn were measured by the recoil-in-vacuum method with comparatively high precision. The experiments were performed at the Holifield Radioactive Ion Beam Facility by Coulomb exciting $\ensuremath{\sim}3$ MeV/u beams in inverse kinematics on carbon and titanium targets. The results for ${}^{124}$Sn and ${}^{126}$Sn are in excellent agreement with recent shell-model calculations. For ${}^{128}$Sn the experiment suggests an increase in the magnitude of $g({2}_{1}^{+})$, as predicted by some models. The present results provide a sensitive probe of the valence orbitals that contribute to the ${2}_{1}^{+}$ wave functions as the double-shell closure at ${}^{132}$Sn is approached.

Anti-analog giant dipole resonances and the neutron skin of nuclei

We examine a method to determine the neutron-skin thickness of nuclei using data on the charge-exchange anti-analog giant dipole resonance (AGDR). Calculations performed using the relativistic proton–neutron quasiparticle random-phase approximation (pn-RQRPA) reproduce the isotopic trend of the excitation energies of the AGDR, as well as that of the spin-flip giant dipole resonances (IVSGDR), in comparison to available data for the even–even isotopes 112–124Sn. It is shown that the excitation energies of the AGDR, obtained using a set of density-dependent effective interactions which span a range of the symmetry energy at saturation density, supplemented with the experimental values, provide a stringent constraint on value of the neutron-skin thickness. For 124Sn, in particular, we determine the value ΔRpn=0.21±0.05 fm. The result of the present study shows that a measurement of the excitation energy of the AGDR in (p,n) reactions using rare-isotope beams in inverse kinematics, provides a valuable method for the determination of neutron-skin thickness in exotic nuclei.

Coulomb excitation of re-accelerated208Rn and206Po beams

In the present study, B( E2; 2(+)-> 0(+) ) values have been measured in the Rn-208 and Po-206 nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics at CERN-ISOLDE. The resulting B(E2; 2(+)-> 0(+)) in 208Rn is similar to 0.08 e(2)b(2). These nuclei lie in, or at the boundary of the region where seniority scheme should persist. However, contributions from collective excitations may be present when moving away from the N = 126 shell closure. To date, surprisingly little is known of the transition probabilities between the low-spin states in this region.

Towards 26Na via (d,p) with SHARC and TIGRESS and a novel zero-degree detector

Nucleon transfer experiments have in recent years begun to be exploited in the study of nuclei far from stability, using radioactive beams in inverse kinematics. New techniques are still being developed in order to perform these experiments. The present experiment is designed to study the odd-odd nucleus 26Na which has a high density of states and therefore requires gamma-ray detection to distinguish between them. The experiment employed an intense beam of up to 3×107 pps of 25Na at 5.0 MeV/nucleon from the ISAC-II facility at triumf. The new silicon array SHARC was used for the first time and was coupled to the segmented clover gamma-ray array TIGRESS. A novel thin plastic scintillator detector was employed at zero degrees to identify and reject reactions occurring on the carbon component of the (CD)2 target. The efficiency of the background rejection using this detector is described with respect to the proton and gamma-ray spectra from the (d,p) reaction.

Neutron spectroscopic factors ofAr34andAr46from(p,d)transfer reactions

Single-neutron-transfer measurements using ($p$,$d$) reactions have been performed at 33 MeV per nucleon with proton-rich $^{34}\mathrm{Ar}$ and neutron-rich $^{46}\mathrm{Ar}$ beams in inverse kinematics. The extracted spectroscopic factors are compared to the large-basis shell-model calculations. Relatively weak quenching of the spectroscopic factors is observed between $^{34}\mathrm{Ar}$ and $^{46}\mathrm{Ar}$. The experimental results suggest that neutron correlations have a weak dependence on the asymmetry of the nucleus over this isotopic region. The present results are consistent with the systematics established from extensive studies of spectroscopic factors and dispersive optical-model analyses of $^{40\ensuremath{-}49}\mathrm{Ca}$ isotopes. They are, however, inconsistent with the trends obtained in knockout-reaction measurements.

First feasibility experiment for the EXL project with prototype detectors at the ESR storage ring

The investigation of light-ion reactions with exotic beams in inverse kinematics gives access to a comprehensive range of nuclear structure information in the region far off stability. The future FAIR facility at GSI will provide new opportunities to extend and advance these investigations. The present paper will focus on the results of the first feasibility experiment for the EXL project in which we used a stored 136Xe beam with E = 350 MeV/nucleon interacting with an internal hydrogen gas-jet target at the ESR storage ring of GSI. In this experiment we made use of at least one element of every detector part of the future experimental setup. Selected results from this measurement will be presented.

First Experiment with HELIOS: The Structure ofB13

A first experiment is reported that makes use of a new kind of spectrometer uniquely suited to the study of reactions with radioactive beams in inverse kinematics, the helical orbit spectrometer, HELIOS. The properties of some low-lying states in the neutron-rich N=8 nucleus 13B were studied with good resolution. From the measured angular distributions of the (d,p) reaction and the relative spectroscopic factors, spin and configuration assignments of the first- and third-excited states of this nucleus can be constrained.

TIARA: A large solid angle silicon array for direct reaction studies with radioactive beams

A compact, quasi- 4 π position sensitive silicon array, TIARA, designed to study direct reactions induced by radioactive beams in inverse kinematics is described here. The Transfer and Inelastic All-angle Reaction Array (TIARA) consists of 8 resistive charge division detectors forming an octagonal barrel around the target and a set of double-sided silicon-strip annular detectors positioned at each end of the barrel. The detector was coupled to the γ -ray array EXOGAM and the spectrometer VAMOS at the GANIL Laboratory to demonstrate the potential of such an apparatus with radioactive beams. The N ( d , p ) 14 N 15 reaction, well known in direct kinematics, has been carried out in inverse kinematics for that purpose. The observation of the N 15 ground state and excited states at 7.16 and 7.86 MeV is presented here as well as the comparison of the measured proton angular distributions with DWBA calculations. Transferred l-values are in very good agreement with both theoretical calculations and previous experimental results obtained in direct kinematics.

New shell model calculations forAr40based on recentg-factor and lifetime measurements

We have redetermined the $g$ factor and the lifetime of the ${2}_{1}^{+}$ state in $^{40}\mathrm{Ar}$ by applying the technique of \ensuremath{\alpha} transfer from a carbon target to $^{36}\mathrm{S}$ beams in inverse kinematics combined with transient magnetic fields. In addition, the lifetimes of the ${4}_{1}^{+}$ and the ${2}_{2}^{+}$ states in $^{40}\mathrm{Ar}$ have been remeasured using the Doppler-shift-attenuation method (DSAM). Additional experimental details of the \ensuremath{\alpha}-transfer measurements are provided. The results are discussed within the framework of new large-scale shell model calculations with both free and effective nucleon $g$ factors.

First g-factor measurements on semi-magic 36S and their implications for the rigidity of the [formula omitted] shell closure

The g-factor of the very short-lived (τ=0.12(1) ps) 21+ state at 3.290 MeV in 36S, g(21+)=+1.3(5), has been determined for the first time by utilizing the Coulomb excitation of 36S beams in inverse kinematics combined with the transient field technique. In addition, for the 31− state (with τ=0.9(1) ps) at 4.192 MeV, a value of g(31−)=+0.8(5) was obtained. In the same experiment, the g-factor of the 21+ state in 40Ar has been remeasured using the α-transfer reaction on the same carbon target. Lifetimes of several excited states in both 36S and 40Ar were also redetermined using the Doppler-shift-attenuation method. The new experimental g-factors and deduced B(E2) values were compared with results of shell-model calculations with the WBT effective interaction and the sdfp shell model space. Comparisons with previous results for 32,34,38,40S and 36,38,40Ar shed light on how the properties of the Ar and S isotopes change as the N=20 shell closure is approached, crossed, and left behind.

Low-level structure of 52Ti based on g factor and lifetime measurements

The g factors of the 21+ and 41+ states in radioactive 52Ti (T1/2=1.7m) have been measured for the first time using the technique of α transfer to 48Ca beams in inverse kinematics, in combination with transient magnetic fields. In addition, employing the Doppler-shift-attenuation method, the lifetime of the 21+ state has been re-determined with much higher precision while the lifetime values of the 41+ and the 23+ states were obtained for the first time. The B(E2) and g factor results were compared with the results obtained within the framework of full fp spherical shell model calculations using several recent effective interactions commonly utilized in this mass region. The two measured g factors were accounted for by none of the calculations except for the FPD6 calculation with modified input single-particle energies. The new data were also discussed in relation to the neighbouring isotopes, 48,50Ti, isotones, 50,52,54Cr, and the magic N=28 shell closure. Our calculations generally reproduce well the trends of the data in terms of their dependence on neutron number.