- FAIR GSI Meeting
- FAIR GSI Meeting - numbered
- Indico style
- Indico style - inline minutes
- Indico style - numbered
- Indico style - numbered + minutes
- Indico Weeks View
The 12th international conference on Direct Reactions with Exotic Beams (DREB2024) will be held in Wiesbaden, Germany, from June 24th to 28th, 2024. This DREB conference is part of the biennial series, which began in 1999 at MSU, East Lansing, at the initiative of physicists working in the field from
MSU, IPN-Orsay, and FSU. The following meetings were held at Orsay (2001), Guildford (2003), East Lansing (2005), Wako (2007), Tallahassee (2009), Pisa (2012), Darmstadt (2014), Halifax (2016), Matsue (2018), and Santiago de Compostela (2022).
The scientific program will be devoted to the latest experimental and theoretical research and developments in nuclear reactions with exotic nuclei. The topics will include the following subjects relevant to direct reactions:
In keeping the tradition of this conference series, the meeting will be of a relatively informal character:
no proceedings will be published. The program of the meeting will consist of contributed presentations
and posters to be selected based on the submitted abstracts, in addition to keynote opening talks. The
conference program will focus on new results, in particular presentations of yet unpublished results. We
strongly encourage students and other junior researchers to participate.
The conference is hosted jointly by GSI/FAIR and the TU Darmstadt.
Single-nucleon knockout reactions at intermediate energies with
In this work, we study the interaction of the core (the residual nucleus after the removal of the nucleon) due to its final-state interaction with the knocked-out nucleon after it has been removed from the projectile. This interaction can lead to the core being excited to energies above its breakup threshold, which leads to its destruction and therefore, a reduction in the knockout cross section, which requires the survival of the core. We describe these effects via an eikonal description of the reaction, where the destruction of the core is modelled via an effective density, which is reduced in the nuclear interior, so that deeply-bound nucleons are more affected by core destruction. We find a significant reduction in the isospin-asymmetry dependence of the ``quenching'' factors [3] when considering the core destruction effect, which points to this reaction mechanism being fundamental for the correct description of the single-nucleon knockout process.
Systematic studies of nuclei along isotopic chains have revealed unexpected trends that challenge our understanding of nuclear structure. For two decades, nuclear physicists have grappled with the asymmetry dependence of the ratio R between the spectroscopic factors extracted experiments and that predicted by the nuclear shell model. Surprisingly, the strong asymmetry dependence of these strengths and their extreme values for highly asymmetric nuclei inferred from knockout reaction measurements on a target nucleus are not consistent with what is extracted from electron-induced, transfer, and quasi-free reaction data [1]. In this talk, I will present the first consistent analysis of one-nucleon transfer and one-nucleon knockout data, in which theoretical uncertainties associated with the nucleon-nucleus effective interactions considered in the reaction models are quantified using a Bayesian analysis [2]. Our results demonstrate that, taking into account these uncertainties, (i) transfer and knockout reactions lead to a consistent picture for the removal of a loosely-bound nucleon and (ii) there is still some tension between the strengths extracted from transfer and knockout data on deeply-bound nuclei. The uncertainties obtained in this work represent a lower bound and are already significantly larger than the original estimates.
[1] Aumann et al. Prog. Part. Nucl. Phys. 118, 103847 (2021)
[2] Hebborn, Nunes, and Lovell, Phys. Rev. Lett. 131, 212503 (2023).
*This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under the FRIB Theory Alliance Award No. DE-SC0013617, under Work Proposals no. SCW0498 and DE-SC0021422. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344 and by Los Alamos National Laboratory under Contract 89233218CNA000001.
The dynamics of quantum few- and many-body systems is often modeled with local interaction models, mainly due to simplicity, though more microscopic or fundamental approaches yield nonlocal interactions. For few-cluster nuclear reactions the interactions usually are given in the local form of real binding and complex optical potentials. We made a two-fold extension of that standard dynamics by developing a new nonlocal form of binding and optical potentials and simultaneously including the excitation of the nuclear core. Exact three-body Faddeev-type equations in momentum-space are solved for the description of nucleon transfer reactions (d,p) and (p,d) and deuteron inelastic scattering (d,d'). Example results for 10Be and 24Mg nuclei demonstrate a good reproduction of the experimental data and an improved consistency between the two-body (elastic and inelastic nucleon-nucleus scattering) and three-body description [1,2].
The description is being extended to nucleon knockout reactions with simultaneous excitation of the core into states absent in the initial nucleus, and thereby beyond the reach of the DWIA. Examples are 12C(p,2p)11B reactions leading to high-spin 5/2- or 7/2- states of 11B.
The ISOLDE Solenoidal Spectrometer (ISS) specialises in the study of direct reactions in inverse kinematics. The ISS was fully commissioned in 2021 with a new silicon detector array and has since undergone three successful physics campaigns. This talk will give an overview of the technical capabilities of ISS, as well as present recent measurements taken using the device. These focus on the single-particle properties of a variety of nuclear systems probed using the single-neutron adding
Direct reactions are fundamental tools to investigate the structure of exotic nuclei. Studies of nuclei far away from stability are usually performed with secondary radioactive beams, that suffer from low intensities and need to be compensated with thick targets and high efficient detection systems to increase luminosity. Active targets are invaluable devices that, among other important features, allow to reconstruct the reaction in three dimensions without loss of resolution.
The ACtive TArget and Time Projection Chamber (ACTAR TPC) detector [1-3] has been developed at GANIL to cover a broad physics programme. The device was commissioned in 2018 showing an excellent performance of the detector [4]. Since then, several experiments have been performed at GANIL. In this talk, We will present the recent results from the first transfer campaign. The main goal of the experiment was the study of the spin-orbit splitting between the proton 0p3/2-0p1/2 orbitals. The reaction
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[5] J. Lois-Fuentes Ph.D. USC (2023)
The exponential decay of unstable states is one of the most pervasive and most studied phenomena in microscopic physics, yet its quantum-mechanical theory remains obscure in many ways. The exponential decay is not a trivial consequence of quantum dynamics; rather, it emerges from a complex equilibrium involving a resonant state with a decaying amplitude and a rotating phase, balanced by the effects of outgoing radiation.
Crucial to our understanding are the early and late-time dynamics, particularly in the context of weakly bound nuclear states in exotic nuclei. Unlike their bound counterparts, these states retain a 'memory' of their formation and background components, a history that manifests in their non-exponential decay dynamics. This memory aspect opens a window into the nuanced transient stages between different decay regimes, often marked by interference among various contributions. These interferences manifest as oscillations in the decay curve and correlations in the decay products, offering rich insights into the decay process.
Our presentation will focus on the latest research efforts aimed at unraveling these complex phenomena. We will explore innovative methodologies and experimental approaches to observe and interpret these dynamics in nuclei. The insights gained promise to enhance our understanding of quantum decay dynamics and its application in nuclear physics.
Neutron-rich nuclei provide important insights to nuclear forces and to the nuclear equation of state. Advances in ab initio methods combined with new opportunities with rare isotope beams enable unique explorations of their properties based on nuclear forces applicable over the entire nuclear chart. In this Letter, we develop novel chiral low-resolution interactions that accurately describe bulk properties from
Theory for knockout reactions
Knockout reactions with protons or light nuclei at intermediate energies have been used for many years as a tool to extract information of stable and exotic nuclei, e.g., single-particle structure, short-range correlations or cluster formation. They are often described theoretically in an eikonal approach that was applied rather successfully in the analysis. However, secondary processes might affect the cross sections, e.g., a knocked-out nucleon can destroy the core or target. There are different, but conflicting suggestions to include such effects, see, e.g., [1,2], and also the importance of the separation-energy is discussed [3]. In this contribution, the basic features of an alternative approach are presented that will be realized in a new reaction code. It relies on a statistical simulation of the reaction process that uses a modified eikonal approach in combination with single-particle wave functions from a mean-field model of the participating nuclei.
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[2] M. Gomez-Ramos, J. Gomez-Camacho, and A.M. Moro, Phys. Lett. B 847 (2023) 138284
[3] C. Hebborn and P. Capel, Phys. Lett. B 848 (2024) 138413
The development of radioactive-ion beams in the mid-80s has enabled the exploration of the nuclear chart far from stability. This technical breakthrough has led to the discovery of nuclear structures unobserved at the bottom of the valley of stability: shell inversion, halo nuclei etc. [1] At the heart of these discoveries are nuclear reactions used to probe the structure of short-lived nuclei. Breakup reactions, inclusive or exclusive, have been extensively used to study the single-particle structure of nuclei far from stability [2]. In particular, spectroscopic factors have been systematically inferred from knockout reactions on light targets, viz.
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The proton-induced
In this contribution, from a reaction theory point of view, I will present the recent progress in the
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While the independent particle picture that nucleons (protons and neutrons) move almost independently inside nuclei is well established, it is also known that several nucleons form a cluster and behave as a single entity in them. Nuclear clustering is a phenomenon that breaks the uniformity of nuclei and can be a key to elucidating the mechanism of alpha decay, determining the equation-of-state of neutron stars, etc. Therefore, experimental and theoretical studies have been intensively conducted [1] to answer such questions as ''What kind of clusters can exist?'' ''What kind of motion do they have in nuclei?'' ''Are they universal on the nuclear chart?'' and ''What mechanism does nuclear clustering realize?''
The proton-induced knockout reaction is one of the experimental methods to observe the presence of clusters and their motion in nuclei [2-9]. In this reaction, a proton collides with a nucleus at an energy of several hundred MeV per nucleon and knocks out a particle from the nucleus. The advantage of using this reaction is that because the incident energy is high, the proton does not perturb the nucleus very much, and we can approximately describe the reaction as the scattering of the proton and the cluster [10]. It allows us to extract information about the cluster in the nucleus with a relatively small uncertainty than other nuclear reactions.
From experimental data of knockout reactions, we can determine the orbital on which the cluster moved, i.e., the radial quantum number
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The signature of the coexistence between single-particle, cluster and collective degrees of freedom of nuclei in reactions is a timely issue.
These rich aspects of the nuclear structure have been standardly described by simple shell models, cluster and collective structure models respectively.
Ultimately, the complexity associated to the coexistence traces back to the bare NN and NNN interactions which induce important NN correlations in nuclear medium, such as short ranged and tensor ones.
We shall reveal recent insights on aspects of many body degrees of freedom in the reaction mechanism for nucleon knockout from a stable/exotic projectile in the collision with a proton target.
We shall present a comprehensive analysis of (p,pN) reactions in inverse kinematics at around 400 MeV/A covering the mass range
Lithium, Beryllium, Carbon and Boron isotopes [1,2]. Total cross sections are calculated using
the many-body {\it ab initio} Quantum Monte Carlo fully correlated wave functions generated with the NN Argonne V18 and the NNN Urbana X (AV18+UX) potentials [3]
and merged into the Faddeev/Alt-Grassberger-Sandhas (F-AGS) [4] reaction formalism, which allows a consistent and simultaneous treatment of all channels, providing an exact solution of the three-body scattering problem for an assumed three-body Hamiltonian. A comparison with available data measured at GSI [5] will be shown.
Additionally, we shall present kinematically semi-inclusive and fully exclusive cross sections for {
[6]. We use a generalized F-AGS with channel coupling,
where the fragment excited states are generated from a rotational model.
The results will be compared with available data measured at the IUCF
where the
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The intrinsic view of quadrupole deformed nuclear rotors is
still prevalent in the community. In it, the shape is characterised by the
about the existence of "rigid" triaxial nuclei, i.e. having a well
defined value of
that are physically relevant in the laboratory frame are the
Kumar invariants Q
can be deduced. We have been able to compute recently, without any
approximation, the higher order invariants (up to Q
possible to evaluate the variances of
are that
1
I will touch upon as well some issues related to the extraction of these
shape parameters by means of ultra relativistic heavy ion collisions.
The
This work was supported by the US Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. This material is based upon work supported by NSF’s National Superconducting Cyclotron Laboratory which is a major facility fully funded by the National Science Foundation under award PHY-1565546; the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357 (Argonne) and under Award Number DE-SC0014552 (UConn); the Spanish Ministerio de Economia y Competitividad through the Programmes "Ramon y Cajal" with the grant number RYC2019-028438-I; the U.K. Science and Technology Facilities Council (Grant No. ST/P004423/1); and the International Technology Center Pacific (ITC-PAC) under Contract No. FA520919PA138. SOLARIS is funded by the DOE Office of Science under the FRIB Cooperative Agreement DE-SC0000661.
Since advent of the RIBF, the NaI(Tl) based scintillation array DALI2+ [1] has been the workhorse for in-beam
HYPATIA is envisaged to be employed at different experimental stations of the upgraded RIBF and its magnetic spectrometers (ZeroDegree, SAMURAI, SHARAQ), each having different performance requirements and constraints. Key experiments to be carried out in the future at the RIBF at intermediate energies involve inelastic scattering on high-Z targets to induce Coulomb excitation, as well as inelastic scattering and quasi-free (p,2p) and (p,pn) reactions on liquid hydrogen.
In my presentation, I will provide an overview of the HYPATIA project, including how well its performance compares to other existing and planned
of the first excited 2
[1] S. Takeuchi et al., NIMA 763, (596) 2014.
Halo nuclei have been a prolific field of Nuclear Physics since its discovery together with the dawn of radioactive beam facilities. The halo is formed by one or two weakly bound nucleons, usually neutrons, orbiting around the rest of nucleons that conforms a compact core. In the case of neutron halo, all the charge is inside core, and, so, a cornerstone in the study of neutron halo is the Dipole Electric Transition Probability, B(E1).
Such B(E1) distribution is usually obtained by performing Coulomb-dominated break-up reactions assuming that, under certain conditions, break-up is only due to dipole Coulomb excitation. Being also 11Be one of the most explored one-neutron halo and usually a benchmark for different models and theories, it is remarkable the fact that two different sets of 11Be on 208Pb data [1,2] led to apparently incompatible B(E1) distributions.
In this contribution we will show how an extension of the Continuum-Discretaized Coupled-Channels method, capable to introduce core excitations (XCDCC) can be used to study Coulomb break-up in order to extract the B(E1). We will discuss a recently proposed procedure which has been able to obtain compatible B(E1) from both data, giving an end to this long-standing discrepancy [3]. Finally, we will apply the same procedure to other cases of interest such us 15C and 19C.
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[3] A.M.Moro, J.A.Lay, and J.Gómez Camacho, Phys. Lett. B 811, 135959 (2020)
The Gamow-Teller Giant Resonance in
The (p,n) charge-exchange reactions in inverse kinematics, coupled with the missing-mass technique, serve as powerful tools for investigating the Gamow-Teller Giant Resonance in radioactive isotopes across a broad excitation energy range (up to 50 MeV), without being constrained by the Q-value limitations of β decay [1]. In our previous work on
The β decay of
In this talk, the results of our completed analysis will be presented. Deduced double differential cross-section up to about 40 MeV, including the Gamow-Teller (GT) Giant Resonance region in
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The
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02- 06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility.
The rapid (r) neutron-capture process produces half the elements heavier than iron and is located on the neutron-rich side of the nuclear chart. Promising site candidates such as core-collapse supernovae (CCSNe) and neutron star mergers still show large discrepancies between observed and calculated abundances. The calculations mostly rely on theoretical neutron-capture cross sections which depend on two reaction processes: direct radiative capture and compound nuclear (CN) mechanism. Neutron capture on 130Sn strongly influences final abundances around the second and third r-process peaks, however, the CN mechanism lacks empirical data.
Turning attention to the neutron-deficient side of the nuclear chart, light nuclei in this region may be produced in the neutrino-induced rapid-proton capture (νp) process, proposed to occur in the innermost ejecta of CCSNe. This is a promising solution to synthesize isotopes not adequately produced in the proton capture (p) process (occurring within the O/Ne layer of CCSNe), particularly 92,94Mo and 94,96Ru. The 56Ni(n,p)56Co reaction is a crucial branching point between the vp- and p- processes and thus governs the abundances of heavier elements, however, its cross section lacks measurement.
To address these knowledge gaps of the 130Sn(n,γ) and 56Ni(n,p) reactions, the surrogate technique was employed using (d,p) transfer reactions on 130Sn and 56Ni, respectively. This experiment campaign was led by the SAKURA collaboration using the BigRIPS-OEDO beamline housed at RIBF in RIKEN, Japan. The heavy radioactive ion beams were produced and separated by the BigRIPS accelerator. Using OEDO the 130Sn (56Ni) beam was decelerated to ~ 22 (15) MeV/u and focused onto a CD2 solid target, thus populating excited states under inverse kinematics. Light charged particles were detected at backward lab angles using the TiNA array. Heavy reaction products were momentum-analyzed at forward angles by the SHARAQ spectrometer and identified using the Bρ-dE-range technique. This approach has a distinct advantage whereby the gamma-emission probabilities of compound nuclear states may be determined with no gamma-ray detection necessary. In this talk, the experimental procedure and preliminary results are presented, with an emphasis on the capabilities of OEDO.
The development of collectivity along the N = Z is one of the subjects that has
recently attracted great experimental efforts. In particular, heavy N=Z nuclei
in the mass region A=80 are expected to be some of the most deformed ground
states which have been found [1] in mid-mass nuclei, typically 8p−8h, 12p−12h
for e.g. the cases of 76Sr, 80Zr. This strong enhancement of collectivity with respect to lighter N=Z nuclei has its origin in cross shell excitations across the N=40 shell gap to g9/2, d5/2 and s1/2 which are intruder quadrupole partners generating deformations. These structures can be interpreted in terms of algebraic Nilsson-SU3 self-consistent model to describe the intruder relative evolution in the vicinity of 80Zr [2]. In this presentation, we will expose some of the latest developments in microscopic nuclear structure calculations for exotic nuclei far from stabilitity at the N=Z [3]. The new theoretical calculations for the very region of 80Zr will be presented for the first time within the interacting shell model framework using an enlarged model space outside a 56 Ni core comprising the pseudo-SU3 p3/2f5/2p1/2 and quasi-SU3g9/2d5/2s1/2 orbitals for both protons and neutrons. We will present and compare results from both exact Shell Model diagonalization [4] and our newly developed DNO Shell Model approach employing beyond mean field techniques [5]. These theoretical calculations allow a very good description of the rapid transition (A=60−100) from spherical to deformed structures which can be intepreted in terms of “simple” many particles - many holes configurations. The whole Island of Collectivity in the region and sudden shape change recently observed between 84Mo and 86Mo is interpreted as an effect on the N = 50 gap induced by the addition of the two neutrons, a fingerprint of three-body forces.
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Phys. 77, 427 (2005).
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Super-radiance was first studied by Dicke [1] within the context of coherence effects in spontaneous radiation processes. Since then, the phenomenon has been referenced in many areas of modern science, among them: quantum optics, condensed matter, biophysics, and nuclear physics (See the reviews in Refs. [2,3]).
In atomic nuclei, seen as a complex open quantum many-body system, the effect arises from the coupling to continuum states that can be treated in terms of a non-hermitian hamiltonian (non-hermitian super-radiance). Increasing coupling to the continuum leads to the separation of long-lived and short-lived (super-radiant) resonance states.
In a recent Nature physics communications [3], Volya and collaborators reported strong evidence for the phenomenon in alpha cluster decays of mirror nuclei 18O and 18Ne. The authors state that “these findings may be the clearest manifestation of the super-radiance in nuclear physics to date.”
In this work we study the effect of continuum coupling on two-neutron transfer reactions such as (t,p). Following the framework discussed in Ref. [3], we consider the simple case of a two-level model to obtain two-neutron transfer amplitudes (TNAs). Our results show a clear transition between the normal and super-radiance regimes, which is marked by a sharp reduction of the ground-state to ground-state transition strength, being now shared between the long-lived and super-radiant resonance states.
Some examples of possible experimental studies, where the effect could be observed, will be discussed.
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[3] I. Rotter, J.P. Bird, Rep. Prog. Phys. 78, 114001 (2015)
[4] A. Volya, M. Barbui, V. Z. Goldberg, and G. V. Rogachev, Nature Comm. Physics 5:322 (2022)
The Active Target Time Projection Chamber (AT-TPC) has been used in experiments aimed at the exploration of structural effects in radioactive nuclei using one step reactions such as transfer or elastic and inelastic scattering. When used as a solenoidal spectrometer by placing it inside a magnetic field, the AT-TPC allows to perform this type of measurement in inverse kinematics with much reduced beam intensities, down to 100 particles per second, while preserving a good resolution and a wide range of angular coverage. This presentation will showcase the performance of this detector, based on recent results obtained on nuclei in the beryllium to carbon region using pure proton, deuterium and alpha targets. Highlights will include results on resonances in
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02- 06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility and used resources of the Facility for Rare Isotope Beams (FRIB) Operations, which is a DOE Office of Science User Facility under Award Number DE-SC0023633.
Several properties of atomic nuclei are known to be sensitive to the neutron-to-proton (isospin) asymmetry. In particular, the evolution of the single-particle strength as a function of isospin has been the subject of experimental and theoretical debate.
Quasi-free scattering (QFS) reaction is an established method to probe the structure of atomic nuclei. This reaction in inverse kinematics using radioactive-ion beams at relativistic energies has been successfully employed as an effective tool to study very exotic nuclei with high luminosity. Recent studies [1, 2] reported on the evolution of the proton single-particle strength as a function of isospin asymmetry using (p,2p) QFS reactions along the Oxygen isotopic chain and found a weak or no dependence. The reduction of the single-particle strength has been attributed to nucleon-nucleon correlations and a recent phenomenological study [3] has quantified the long and short-range part of these correlations and their dependency with isospin. The QFS result is at variance with nucleon-removal reactions with heavy targets [4] where they report a single-particle strength is strongly correlated with isospin.
To shed light on this puzzle, we performed a systematic study of (p,2p) and (p,pn) cross sections along the calcium isotopic chain (from 39Ca to 50Ca) at 500 MeV/nucleon using proton and carbon targets. The experiment was performed with the large acceptance spectrometer GLAD with the R3B setup at GSI-FAIR. The difference in reactions with the targets and the identification of reactions with recoil protons are investigated. The results of the analysis and comparison to the theoretical calculations will be discussed in this contribution.
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Astrophysical objects such as neutron star formation and structure and supernovae explosion, as well as nuclei properties and structure are described using the equation of state of nuclear matter. However, the coefficients of the equation state describing the nuclear matter with a huge charge asymmetry, notably the symmetry energy, is lacking constraints [1,2].
When a medium-to-heavy neutron-rich nuclei near the neutron drip-line is submitted to an external electric field, its response is concentrated in the Giant Dipole Resonance (GDR) and particularly in its low lying part, referred as the Pygmy Dipole Resonance (PDR). The electric dipole polarizability aD, which represents the inversely energy-weighted sum of dipole strength, allow to quantify this response.
Neutron skin presents a strong correlation to symmetry energy and can be constrained through the use of aD [3,4], and theoretical calculation has shown that the PDR strength has a rapid increase with the neutron number number in the range 15 < N ≤ 16, 28 < N ≤ 34, and 50 < N ≤ 56 [5]. In this context, both 50Ca and 52Ca, who respectively have 30 and 32 neutrons, has been a subject to experimental investigation: they were produced in flight at RIBF – RIKEN and they have been submitted to coulomb excitation using a 208Pb target in order to probe the neutron number dependence of PDR. We will present preliminary results for 50Ca.
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Neutron-rich calcium isotopes show interesting features exhibiting non-canonical neutron shell closures at N=32 and N=34, while their charge radii [1] show a sharp increase after N=28 which is not reproduced by microscopic theories. Matter radii [2] from interaction cross-section measurements indicate that the increase in size of neutron-rich calcium isotopes is mainly due to neutrons and that a core swelling mechanism is at play [3].
Recently, the proton-induced neutron knockout reaction on
This analysis was extended to
The nucleon knockout direct reaction proves to be a valuable tool, sensitive to the size of the single-particle orbitals - a quantity that has not been deeply explored so far for exotic beams.
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The neutron-deficient calcium isotopes have attracted considerable attention recently. Present studies are divided over the amount of proton pf-shell occupancy, ranging from an intact
Two-neutron removal, a direct reaction sensitive to the single-particle configurations and couplings of the removed neutrons in the projectile wave function, from
The results yield conclusive evidence for the need of sizeable proton cross-shell excitations into the pf shell already for the
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Neutron-rich Ca isotopes towards neutron number N = 34 are pivotal for exploring the evolution of the fp-shell orbitals [1]. Beyond the N = 28 shell gap at 48Ca, new magic numbers at N = 32 and 34 were established through spectroscopy of low-lying states [2] and mass measurements [3]. Most recently, the spatial extension of the 1f7/2 and 2p3/2 neutron orbitals was determined via a one-neutron knockout reaction from 52Ca [4], while the single-particle 2p1/2 , 1f5/2 and 1g9/2 orbitals defining the shell gaps at N = 32, 34 remain to be established experimentally. The 50Ca(d, p)51Ca transfer reaction presents itself as well suited-method to access spectroscopic factors in the fp-shell, where the angular distribution of the reaction products allow for deduction of the angular momentum transfer.
In Decemeber of 2022 the SHARAQ12 experiment was performed at the RIKEN Nishina Center, aiming to study the single-particle structure of 51Ca via the (d, p) reaction using a 50Ca secondary beam. The secondary beam was produced at the BigRIPS separator and then degraded to approximately 15 MeV/nucleon at the OEDO [5] beamline. Beam-tracking has been performed with the recently developed Strip-Readout PPAC detectors [6], recoiling protons coming from the interaction of the beam with the secondary target of CD2 (260 μg/cm2) have been identified with the detector setup TINA2 [7], while the heavy recoils have been identified at the QQD SHARAQ spectrometer. In this contribution, I will present the experiment, current status of the analysis, and the implications on the structure of neutron-rich Ca isotopes.
The direct reaction theory widely used to study single-particle spectroscopic strength in nucleon transfer experiments is based on a Hamiltonian with two-nucleon interactions only. We point out that in reactions where three-body effects are important, for example, such as
We study the effects of the
Relativistic Coulomb excitation in inverse kinematics can be utilized to study the electric dipole response of projectile neutron-rich nuclei. In such conditions, collective excitations arise where neutron and proton densities of the excited nucleus are displaced with respect to each other. Additionally, access to greater isospin asymmetries on the neutron-rich side of the nuclide chart provide a suitable environment to probe the symmetry energy, a crucial yet still fairly unknown ingredient of the nuclear equation of state.
In Ref. [1] a novel approach to constrain the slope of the symmetry energy
This approach was further examined in the experiment carried out using the large acceptance spectrometer R
[1] A. Horvat, Doctoral thesis, Technische Universität Darmstadt (2019).
[2] R
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The Sn isotopes, containing the longest chain of isotopes between two doubly-magic nuclei, offer a fundamental testing ground for nuclear theories. Between the
An experiment to measure for the first time the
An anomaly in the energy differences of mirror nuclei and isobaric analogue states (IAS), not yet well understood from a microscopic point of view, was found more than 50 years ago and is called the Okamoto-Nolen-Schiffer (ONS) anomaly. A systematic study from light to heavy nuclei within the framework of the independent-particle model found that the theoretical values of the energy difference underestimate always the experimental values by 3–9%.
A possible main source to cure the gap is the charge symmetry breaking (CSB) nuclear interaction. However, both the magnitude and the sign of the parameters in CSB interactions have not been well determined from phenomenological studie.
The aim of this study is to provide a quantum chromodynamics (QCD)-based understanding of CSB by making a quantitative link between the Skyrme-type CSB interactions and the CSB effect due to the u-d quark mass difference in QCD. A novel approach is proposed to link the CSB nuclear interaction and the low-energy constants in QCD and the density dependence of chiral condensation of q ̄q pair in the nuclear medium for the first time.
The resulting QCD- based CSB interaction is applied to resolve the ONS anomaly: the numerical results for the mirror nuclei (A = 16±1 and A = 40±1 with the isosymmetric core N = Z = A/2) with the two Skyrme EDFs show good agreement with experimental data both in sign and magnitude within the theoretical error bars. Other several possible effects on ONS anomaly were also considered in the study. Major theoretical uncertainty of the final results originates from the low-energy constants of QCD. Increasing the accuracy of these constants from the experimental data or from the lattice QCD simulations will be instrumental. The QCD-based CSB interaction discussed here would have strong impact on isospin symmetry breaking phenomena such as IAS, the super-allowed β decay in the context of Cabibbo-Kobayashi-Maskawa unitary matrix, and the mass predictions of isobar and isotriplet nuclei near the proton drip line.
Further extension of QCD-based isospin breaking forces (IBS) including the charge invariance breaking (CIB) will be discussed in the study of IAS and also hypernuclei.
The s-wave neutron-nucleus scattering length
However, in
We have determined this essential observable by using a series of nuclear reactions leading to the
The (
The deuteron elastic and inelastic scattering reactions of
This material is based upon work supported by NSF’s National Superconducting Cyclotron Laboratory which is a major facility fully funded by the National Science Foundation under award PHY-1565546; the U.S.\ Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357 (Argonne). SOLARIS is funded by the DOE Office of Science under the FRIB Cooperative Agreement DE-SC0000661.
Nuclei that present a three-body character have attracted special interest over the past few decades. Of particular relevance is the case of Borromean two-neutron halo nuclei, e.g., 6He, 11Li or 14Be, which exhibit exotic features in nuclear collisions [1]. The correlations between the valence neutrons, often described in terms of pairing, are known to play a fundamental role in shaping the properties of these systems [2,3]. The evolution of these correlations beyond the driplines gives rise to two-neutron emitters, e.g., 13Li, 16Be or 26O [4]. Since they have a marked core+N+N character, three-body models are a natural choice to analyze their structure and processes involving them [5, 6]. The description of the continuum in three-body nuclei, however, is not an easy task. In Ref. [7] we proposed a method to characterize few-body resonances from the time evolution of the lowest eigenstates of a resonant operator in a discrete basis, with the aim of studying the population of these systems in knockout reactions. The relative-energy distributions in their decay can be computed by solving an inhomogeneus equation with a source term involving the resonance eigenstate [8]. The method has been applied to 16Be [9] and 13Li [10], showing signatures of direct two-neutron decay, and in good agreement with recent experimental observations. These unpublished results will be presented, together with prospects for future developments and applications.
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[8] J. Casal and J. Gómez-Camacho, in preparation (2024).
[9] B. Monteagudo et al., submitted for publication (2024).
[10] P. André et al., submitted for publication (2024).
In order to constrain the largely unknown multi-neutron interactions, it is necessary to measure the relevant observables sensitive to them. One such property is the possible existence of narrow resonances related to multi-neutron cluster structures and correlations
With the aim of systematically studying such resonances and characterizing the corresponding nn-relative system, an experiment was performed at the R
In this communication the results of the nn-relative energies for selected isotopes in the "cocktail" beam will be discussed along with relevant spectroscopic information. The discussion will include the analysis of the
Unbound states in the neutron-rich
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02- 06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility and used resources of the Facility for Rare Isotope Beams (FRIB) Operations, which is a DOE Office of Science User Facility under Award Number DE-SC0023633.
Nuclear resonant states far from the stability line provide a stringent test of nuclear forces at extreme isospin asymmetry. In this talk, I will report on the low-lying resonant states of extremely neutron-rich
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[5] Y. Kubota et al., Phys. Rev. Lett. 125, 252501 (2020).
The ratio method [1-3] is a novel method to extract important structural information of halo nuclei, such as binding energies and ANCs (Asymptotic Normalizing Coefficients). It is based on the Recoil Excitation Breakup (REB) model [4], which predicts that the uncertainty of halo structures related to the reaction dynamics is strongly reduced by taking the ratio of angular distributions for breakup and scattering. Accordingly, this new reaction observable exhibits a largely improved accuracy compared to traditional methods, such as Coulomb breakup. We will present the first experimental test of the method for the 11Be + 12C collision at Elab=20 MeV/u. The experiment was performed at the Texas A&M University cyclotron. Angular differential cross sections for elastic and inclusive neutron breakup cross sections were measured with a Si + phoswich detector array, BlueSTEAl [5], at CM angles =10-30 deg. The measured cross sections were well-reproduced by theory calculations using CDCC and Dynamical Eikonal Approximation (DEA) [6]. The ratio of the inclusive breakup to elastic cross section demonstrates the validity of the new method. Further calculations have shown that it is independent of optical potentials used to describe the projectile-target interaction and is sensitive to the halo structure. We have extended our analysis to available 11Be + 208Pb data, confirming that the ratio method works well both for nuclear-dominated and Coulomb-dominated reactions. This augurs well for our plan to extract structure information of further exotic halo nuclei (e.g., A=20-40). In this contribution, we will present the research results above and discuss our future plans to apply the ratio method with exotic beams at FRIB.
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*The work at Brookhaven National Laboratory was sponsored by the Office of Nuclear Physics, Office of Science of the U.S. Department of Energy under Contract No.DE-AC02-98CH10886 with Brookhaven Science Associates, LLC.
The latest generation of radioactive ion beam facilities provides unparalleled access to neutron-rich unstable isotopes. One of the areas of active investigation is the study of the shell evolution near the neutron magic numbers N=20 [1-4] and N=28 [5-6] for such unstable nuclei. The nuclei near these magic numbers display exotic structural features such as dampening of shell gaps, formation of halos, and deformed structures.
Recently, the 29F system, a light neutron-rich N=20 isotone, was identified as the heaviest two-neutron Borromean-halo nucleus found till date [1-4]. Motivated by this observation, it is interesting to explore the “N=28” shell closure for nuclei with a small proton number as well, to see whether we can find similar Borromean structure formation.
In this talk, I will compare and contrast the shell evolution across the neutron magic numbers N=20 and 28 within a three-body (core+N+N) framework based on the hyperspherical-harmonics formalism by using an analytical-transformed harmonic-oscillator basis. New three-body results will be presented for the ground state structural properties of putative two-neutron Borromean halos in Na and Mg isotopes with N=28 [7].
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[3] J. Casal, J. Singh, et al., PRC 102, 064627 (2020).
[4] L. Fortunato, et al., Commun. Phys. 3, 132 (2020).
[5] D. S. Ahn, et al., PRL 129, 212502 (2022).
[6] K.Y. Zhang, et al., PRC 107, L041303 (2023).
[7] Jagjit Singh et al., arXiv:2401.05160 [nucl-th] (2024).
The large branching ratio observed in the
branching ratio populating it. Since then, there were several experiments that reported the observation of such an elusive resonance. While there is a widespread agreement on the existence of this resonance, from both theoretical and experimental stand points, there are still many open questions around its nature. One of the main challenges lies in the description of the complex structure of
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02- 06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility and used resources of the Facility for Rare Isotope Beams (FRIB) Operations, which is a DOE Office of Science User Facility under Award Number DE-SC0023633. This work has received financial support from Xunta de Galicia (CIGUS Network of Research Centers) and from the Spanish Ministerio de Economía y Competitividad through the Programmes “Ramón y Cajal” with the Grant No. RYC2019-028438-I.
One and two proton removal from neutron-rich medium-mass nuclei are commonly used to populate different final states in a nucleus of interest. (p,2p) and (p,3p) knockout reactions have been investigated in inverse kinematics within the first two SEASTAR campaigns that took place at RIBF in RIKEN, Japan [1]. These studies have been extended to the third SEASTAR campaign where medium-mass radioactive nuclei in the region of 54Ca were sent at about 270 MeV/nucleon onto a 15 cm long liquid hydrogen target surrounded by the MINOS time-projection chamber. MINOS enabled to track the angular distribution of the knocked out protons. (p,2p) and (p,3p) cross sections have been obtained and compared to theoretical reaction models. In particular, the difference in sensitivity of (p,2p) and (p,3p) to the population of individual final states in the same nucleus will be discussed.
References:
[1] A. Frotscher et al., Phys. Rev. Lett. 125, 012591 (2020)
Constructing effective interactions (`optical potentials’) between a proton or neutron and a nucleus for computing elastic scattering has a long tradition. A renewed interest in considering this challenging task stems from the possibility of combining today’s ab inito structure work with elastic scattering from light up to medium-heavy nuclei using the framework of the spectator expansion of multiple scattering theory to compute its leading order term consistently. The calculation of the effective interaction in leading order in the spectator expansion relies on two basic input quantities, which are the fully off-shell nucleon-nucleon (NN) amplitudes in their Wolfenstein representation and the translationally invariant non-local scalar and spin-projected density matrices of the target nucleus.
For light nuclei (up to
Calculations of elastic scattering observables, namely differential cross sections and spin observables, for proton scattering for nuclei with 0+ ground states from Carbon to Calcium in the energy range from 65 to 200 MeV will be presented and compared to experimental data.
The SCRIT (Self-Confining RI Ion Target) electron scattering facility [1] was constructed at RIKEN in Japan to enable electron scattering from short-lived unstable nuclei. Electron scattering is a powerful tool for exploring the structure of atomic nuclei because of the well-understood mechanism of electromagnetic interaction. However, its application to short-lived unstable nuclei has been challenging because of the difficulty in preparing thick targets, even though there has been a long-standing desire to investigate exotic features of unstable nuclei using electron scattering [2].
Recently, we achieved a milestone by realizing the world's first electron scattering from online-produced unstable nuclei,
In this contribution, we will present recent progress and prospects of the SCRIT electron scattering facility and discuss several topics also that may be only feasible in the future using the SCRIT method.
References:
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[2] T. Suda and H. Simon, Prog. Part. Nucl. Phys. 96, 1 (2017)
[3] T. Ohnishi et al., Nucl. Instr. Meth. B541 (2023) 380-384
[4] K. Tsukada et al., Phys. Rev. Lett. 131 (2023) 092502
The equation of state of nuclear matter(EOS), which describes the macroscopic properties of nuclei, is essential not only to describe the structure and collisions of nuclei but also to understand the astrophysical problems, such as the mechanism of supernova explosions and the structure of neutron stars. Since nuclear matter is composed of two Fermi particles, protons and neutrons, the equation of state has a term that depends on the density difference between the two, which is called the symmetry energy. From previous studies, it is known that the first-order density dependence of the symmetry energy is closely related to the thickness of the neutron skin [1].
In this study, interaction cross sections
In the neutron-rich region of Ni isotopes, the present
In this presentation, we’ll report the matter radii and charge radii derived from the experimental cross sections using Glauber calculations. Also, in the region where the charge radii are known, from A = 58 to 70, we’ll discuss the neutron skin thickness of Ni isotopes, which is obtained by the present data combined with known charge radii. On the other hand, in the neutron-rich region with A
References
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The experimental evidence points to the existence, at short distances, of strongly correlated neutron-proton pairs much like they are in the deuteron or in free scattering processes. As it moves through the nuclear medium, a “bare” nucleon in the presence of the nucleon-nucleon interaction becomes “dressed” in a quasi-deuteron cloud [1], about 20% of the time. A phenomenological analysis of the quenching of spectroscopic factors [2] and recent data from Jefferson Lab [3] point to an isospin dependence of the independent-particle model content in a dressed nucleon. It is expected that this dependence should also be reflected in the dressed amplitude and thus, in the virtual quasi-deuteron content in the ground state.
Following from the qualitative arguments above, quasi-free scattering (QFS) of deuterons for which the fast reaction time
In this contribution, we will discuss these ideas within a single-j approximation and put forward an experimental case that can serve as a template to test the above conjecture, i.e., measuring the (p,pd) QFS cross-section for knocking out a deuteron in
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*This work was supported by the Royal Society, UK STFC, and the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy
The isospin character of the p-n pair and n-n pair at medium relative momentum has been observed in comparison with A=6 nuclei, 6Li, and 6He. We have measured the 6Li(p,dp) and 6He(p,dn) cross sections for the neutron pick-up domain with 70A MeV incident heavy ion on the solid hydrogen target[1] via inverse kinematics at RIPS facility in RIKEN. All the reaction products at forward angles, including recoiled nucleons N [p or n], were measured by plastic scintillator telescopes and identified unambiguously. The momentum transfer covers up to 1.0 fm-1 through a wide angular coverage, thus picking up the high-momentum neutrons correlated with protons in nuclei. In the (p,dp) reaction, we observed a strong population of deuteron-like states d+4He in 6Li but a weak population of neutron pairs ’n-n’+4He in 6He.
The data were compared with plane-wave and distorted-wave impulse approximation (DWIA) calculations with realistic elastic d(p,p)d and charge exchange reaction ’n-n’(p,n)d cross sections with the common procedure, which was successfully applied to the 16O(p,dp)[2]. The calculations with assumed spectroscopic amplitudes from theoretical estimation based on a three-body model[3] fairly reproduce the observed ratio of cross sections between 6Li and 6He. It indicates that the present DWIA framework works well at medium relative momenta. The observed strong isospin dependence in the NN pair indicates the presence of NN correlation in A=6 nuclei. In this talk, we will present new results of the experiment with 6Li(p,dp)4He and 6He(p,dn)4He and discuss the applied detailed reaction analysis.
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Unlike standard like-particle pairing (neutron-neutron, proton-proton) that only exists in the T=1 channel, proton-neutron pairing can exist in both T=1 and T=0 channels. The consequences of this coexistence are not yet fully understood, but could explain phenomena such as the overbinding of self-conjugate nuclei.
Proton-neutron pairing can be studied by spectroscopy as in ref. [1], or by transfer reactions, as in ref. [2] , since the two-nucleon transfer reaction cross-section is expected to be enhanced by pairing. The relative proton-neutron pairing strengths between T=1 and T=0 channels can be accessed by measuring transfer cross-sections to the low-lying (J=0
As pairing is a collective effect, it is expected to be stronger in the middle of high j orbitals. The f
The experiment to measure the two-nucleon transfer reaction
I will present preliminary cross-sections and angular distributions for the low-lying states of
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The formation of short-range correlated nucleon-nucleon pairs (SRCs), primarily composed of neutron-proton pairs [1], appears to be a universal feature in atomic nuclei [2]. Interestingly, measurements in electron scattering indicate that protons become significantly more correlated in asymmetric nuclei as a function of neutron excess. This has potential implications for the description of cold dense nuclear matter as for neutron stars. However, available data are limited to stable nuclei which have maximum neutron excess of ~1.6 and, at the same time as they become more neutron-rich, they also become more heavy. To overcome these limitations, we performed a pilot experiment at the R³B setup at GSI-FAIR [3] as part of the FAIR Phase-0 experimental program to measure SRC in the most neutron-rich nucleus yet,
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[3]https://www.gsi.de/work/forschung/nustarenna/nustarenna_divisions/kernreaktionen/activities/r3b.