Nuclear Structure Studies Research Articles

Nuclear physics with TriSol at Notre Dame’s Nuclear Science Laboratory

The detailed study of radioactive nuclei has resulted in opportunities for addressing many open questions in low-energy nuclear physics. For over three decades, the TwinSol separator at the University of Notre Dame has produced high-quality in-flight radioactive beams at low-energy for light isotopes that have been used in experiments aimed at nuclear structure, astrophysics, and fundamental symmetries studies. We have recently upgraded the TwinSol separator by adding additional elements: a dipole magnet, and a third solenoid. This new TriSol separator will improve the quality and purity of future radioactive beams. This improvement will enable the use of heavier beams and address beam contamination that has hindered past experiments. The current status of TriSol and its science program will be presented along with the role the TriSol program plays in the current landscape of nuclear physics user facilities. The TriSol program includes plans for studies of 11C(p, p)11C reaction for investigating the nature of the first stars, 14O(α, p)17F and its influence on reaction networks in X-ray bursts, the measurement of fusion reactions on Ne isotopes important for pycnonuclear reactions, precision half-life measurements for fundamental symmetries studies, and the use of TriSol as a magnetic spectrometer.

Nuclear structure advancements with multi-nucleon transfer reactions

Multi-Nucleon Transfer (MNT) reactions have been used for decades as a reaction mechanism, in order to populate excited states in nuclei far from stability and to perform nuclear structure studies. Nevertheless, the development of set-ups involving high acceptance tracking magnetic spectrometers (mainly existing in Europe), coupled with the Advanced GAmma Tracking Array (AGATA) opens new possibilities, especially if they are used in conjunction with high-intensity stable beams or ISOL RIBs. In this article, we will discuss the capabilities of such set-ups aiming at different goals, including complete information in high-resolution spectroscopy as well as lifetime measurements.

Methods for systematic study of nuclear structure in high-energy collisions

Methods for systematic study of nuclear structure in high-energy collisions

AGATA: performance of $$\gamma $$-ray tracking and associated algorithms

AGATA is a modern $$\gamma $$ -ray spectrometer for in-beam nuclear structure studies, based on $$\gamma $$ -ray tracking. Since more than a decade, it has been operated performing experimental physics campaigns in different international laboratories (LNL, GSI, GANIL). This paper reviews the obtained results concerning the performances of $$\gamma $$ -ray tracking in AGATA and associated algorithms. We discuss $$\gamma $$ -ray tracking and algorithms developed for AGATA. Then, we present performance results in terms of efficiency and peak-to-total for AGATA. The importance of the high effective angular resolution of $$\gamma $$ -ray tracking arrays is emphasised, e.g. with respect to Doppler correction. Finally, we briefly touch upon the subject of $$\gamma $$ -ray imaging and its connection to $$\gamma $$ -ray tracking.

Production and anisotropic flow of thermal photons in collisions of α -clustered carbon with heavy nuclei at relativistic energies

The presence of $\ensuremath{\alpha}$-clustered structure in the light nuclei produces different exotic shapes in nuclear structure studies at low energies. Recent phenomenological studies suggest that collision of heavy nuclei with $\ensuremath{\alpha}$-clustered carbon ($^{12}\mathrm{C}$) at relativistic energies can lead to large initial state anisotropies. This is expected to impact the final momentum anisotropies of the produced particles significantly. The emission of electromagnetic radiations is considered to be more sensitive to the initial state compared to hadronic observables and thus photon observables are expected to be affected by the initial clustered structure profoundly. In this work we estimate the production and anisotropic flow of photons from most-central collisions of triangular $\ensuremath{\alpha}$-clustered carbon and gold at $\sqrt{{s}_{NN}}=200$ GeV using an event-by-event hydrodynamic framework and compare the results with those obtained from unclustered carbon and gold collisions. We show that the thermal photon ${v}_{3}$ for most central collisions is significantly large for the clustered case compared to the case with unclustered carbon, whereas the elliptic flow parameter does not show much difference for the two cases. In addition, the ratio of anisotropic flow coefficients is found to be a potential observable to constrain the initial state produced in relativistic heavy-ion collisions and also to know more about the $\ensuremath{\alpha}$-clustered structure in carbon nucleus.

Transformation of ICEBall to fIREBall for conversion electron spectroscopy

Conversion electron spectroscopy is a valuable tool in nuclear structure studies, but the complex spectra resulting from the high density of levels in the spectra of heavy nuclei make it difficult to extract the most beneficial information from singles measurements. This work reports on the transformation of ICEBall, which was a mini-orange spectrometer that was used in coincidence with various Germanium detector arrays, to the improved fInternal conveRsion Electron Ball (fIREBall) spectrometer for the improved measurements of E0 transitions and conversion electron coefficients. A combination of FreeCAD, COMSOL, and Geant4 simulations were implemented to optimize the geometries for the magnet filters used in the spectrometer to significantly improve the efficiency of electron collection in the energy range of interest 200 keV-1 MeV. The array of six mini-orange Si(Li) detectors are to be replaced with six new, thicker Si(Li) detectors. Experimental tests reported here show a peak improvement in absolute efficiency from 2.8% to 5.3% for the 482 keV K electron line in 207Bi for a single magnet filter and detector pair.

Foreword

These Proceedings contain invited and contributed papers presented in the 13th International Seminar on Nuclear Physics held in Sant’Angelo d’Ischia from May 15 to May 20, 2022. This Seminar is part of a series of topical meetings started in Sorrento in 1986 on the initiative of Aldo Covello and continued regularly with meetings taking place every two or three years in the Naples area.The main aim of the Seminar, entitled “Perspectives and Challenges in Nuclear Structure after 70 Years of Shell Model”, was to focus on the progress made in recent years in the nuclear structure field from both theoretical and experimental points of view as well as on the role that nuclear structure plays in the context of fundamental physics. The specific topics covered during the conference represent the main lines of investigation in this field:• Advanced methods for nuclear structure• Nuclear structure studies through RIB experiments• Nuclear structure & fundamental physics• Special topicsThere were about 70 participants, which should be considered a great success despite the 30% reduction compared to the previous editions. The 13th Seminar, was, in fact, one of the first in-person meetings after the break due to the Covid-19 pandemic, which hampered, together with the Russia attack in Ukraine, participation from countries outside Europe. It is worth mentioning that six young international researchers between participants benefited from the financial support provided by the “Young Investigator Training Program 2019” funded by ACRI (organization of Foundations of banking origin and Savings Banks), which also allowed them to carry out one-month research activity at Italian Institutions.The Seminar started with a session in memory of Aldo Covello, who passed away on March 31, 2020. Friends and colleagues, as Luigi Coraggio, Giacomo de Angelis, Francesco Iachello, Nicola Lo Iudice, highlighted his human qualities and scientific achievements. A comprehensive overview of the Seminar topics was given in the following sessions through about 60 general talks and more specialized contributions. We had also the opportunity to celebrate Francesco Iachello’s 80th birthday with a special session on Wednesday, before Banquet.The present volume contains 31 manuscripts. All these manuscripts have been peer reviewed. We would like to thank all the colleagues who have acted as referees to assess the suitability of the various articles for publication in Journal of Physics: Conference Series. We are confident that the high quality of all papers contained in these Proceedings will be appreciated by the nuclear physics community.List of Local Organizing Committee, International Advisory Committee, Sponsors of The Seminar are available in this pdf.

Nuclear structure studies in mirror nuclei

The nuclear structure of the A=31 and A=47 mirror couples produced by two fusion evaporation reactions has been elaborated, utilizing the Doppler-shift attenuation method. Excited states in 31P and 31S were populated using the 1p and 1n exit channels, respectively, of the reaction 20Ne + 12C, while in 47Cr and 47V couple excited states were populated based on 28Si + 28Si reaction, as products of 2αn and 2αp exit channels. The A=31 mirror couple was studied utilizing Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro with GASP multidetector array and for A=47 one - with the EUROBALL array using XTU Tandem also in Legnaro. In both cases the lifetime measurements in mirror couples at the same experiment open possibilities for investigations of isospin symmetry. Determined B(E1) strengths in the mirror nuclei 31P and 31S allow to extract the isoscalar component, which can reach up to 24% of the isovector one. The B(E1) values can be modeled by the Equation of motion method. In the case of A=47 mirror couple, the quadrupole moments can be described by shell-model calculations.

What can we learn from experiments with high-brilliance gamma beams?

An overview of the main directions of present-day studies with quasimonochromatic γ beams is presented with an emphasis on the research opportunities which will be provided to the users at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) facility at Magurele near Bucharest. Experiments with γ beams at the extremes of high temperature and high neutron-to-proton ratios will be discussed. The opportunities for nuclear structure studies with γ rays with orbital angular momentum (OAM) are outlined and a few selected physics problems and classes of experiments, related to, e.g., changes of photonuclear cross sections in reactions with OAM photons, as well as the possibility to address nuclear excitations with higher multipolarity are discussed. The perspectives for studies of exotic nuclei within the Gamma Factory experiment at CERN are discussed, too.

Catalytic site mutations confer multiple states of G protein activation.

Heterotrimeric guanine nucleotide-binding proteins (G proteins) that function as molecular switches for cellular growth and metabolism are activated by GTP and inactivated by GTP hydrolysis. In uveal melanoma, a conserved glutamine residue critical for GTP hydrolysis in the G protein α subunit is often mutated in Gαq or Gα11 to either leucine or proline. In contrast, other glutamine mutations or mutations in other Gα subtypes are rare. To uncover the mechanism of the genetic selection and the functional role of this glutamine residue, we analyzed all possible substitutions of this residue in multiple Gα isoforms. Through cell-based measurements of activity, we showed that some mutants were further activated and inactivated by G protein-coupled receptors. Through biochemical, molecular dynamics, and nuclear magnetic resonance-based structural studies, we showed that the Gα mutants were functionally distinct and conformationally diverse, despite their shared inability to hydrolyze GTP. Thus, the catalytic glutamine residue contributes to functions beyond GTP hydrolysis, and these functions include subtype-specific, allosteric modulation of receptor-mediated subunit dissociation. We conclude that G proteins do not function as simple on-off switches. Rather, signaling emerges from an ensemble of active states, a subset of which are favored in disease and may be uniquely responsive to receptor-directed ligands.

Nuclear Structure Investigations of Even–Even Hf Isotopes

The mass region of rare-earth nuclei in the nuclear chart is riddled with well-deformed nuclei, exhibiting rotational properties and many interesting nuclear structure-related phenomena. The scarcity of experimental data as the neutron number increases and the exotic phenomena such as shape coexistence, which are strongly connected with the underlying symmetries of the Hamiltonian and are predicted to take place in this region, make this mass region a fertile ground for experimental and theoretical studies of nuclear structure. In this work, we investigate the structure of the even–even 162–184Hf (hafnium) isotopes through a calculation of various observables such as B(E2;01+→21+) reduced transition matrix elements and quadrupole moments. Six different nuclear models are employed in the calculations of the observables for these nuclei, the shapes of which deviate from spherical symmetry, and as such, are characterized by Hamiltonians, which break the rotational invariance of the exact nuclear many-body Hamiltonian. The results of the present study are expected to establish some concrete guidelines for current and future experimental endeavors. Along these lines, the results for the 162–180Hf isotopes are compared with existing experimental data where available, showing an overall good agreement.

Fermi operator expansion method for nuclei and inhomogeneous matter with a nuclear energy density functional

The nuclear energy density functional method at finite temperature is a useful tool for studies of nuclear structure at high excitation, and also for researches of nuclear matter involved in explosive stellar phenomena and neutron stars. However, its unrestricted calculation requires large computational costs for the three-dimensional coordinate-space solvers, especially for the Hamiltonian matrix diagonalization and (or) the Gram-Schmidt orthonormalization of the single-particle wave functions. We test numerical performance of the Fermi operator expansion method, that requires neither the diagonalization nor the Gram-Schmidt orthonormalization, for finite nuclei and inhomogeneous nuclear matter. The method is applied to isolated finite N=Z nuclei and to non-uniform symmetric nuclear matter at finite temperature, which turns out be very effective with the three-dimensional coordinate-space representation, especially at high temperature. The Fermi operator expansion method is a useful tool for studies of various nuclear phases at finite temperature with the energy density functional calculations. The method is suitable for massively parallel computing with distributed memory. Furthermore, when the space size is large, the calculation may benefit from its order-N scaling property.

Calculation of the electromagnetic moments and electroexcitation form factors for some boron isotopes using shell model with skyrme interaction

The magnetic dipole and electric quadrupole moments for some Boron isotopes were calculated using the shell model taking into account the effect of the two-body effective interactions and the single-particle potentials. These isotopes are; (8 5)B(2 +), (1 50)B(3 +), (1 51)B((3/2)−), ( 1 52)B(1 +) and (1 53)B((3/2)−). Also, the elastic and inelastic longitudinal and transverse electron scattering form factors are calculated for 10B and 11B, for which there are available experimental data. The one-body transition density matrix elements (OBDM) were calculated using the two-body effective interactions; PWT, PEWT, PKUO and CKIHE, which are carried out in the p-shell model space. Skyrme interaction was implemented to generate the single-particle matrix elements with Hartree-Fock approximation and compared with those of harmonic-oscillator and Wood-Saxon potentials. All the evaluated results were compared with available experimental data. The present work has led us to conclude that the shell model calculations with Skyrme type interaction give a good tool for nuclear structure studies. All signs for the experimental electromagnetic moments data are reproduced correctly. The longitudinal and transverse form factors for positive and negative parity states are fairly well reproduced when using a suitable model space.

Nuclear astrophysics studies with γ-ray beams: What do we expect to learn from them?

An overview of the main directions of present-day studies with quasimonochromatic γ beams is discussed with an emphasis on the research opportunities which will be offered at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) facility at Magurele near Bucharest in Romania. Experiments with γ beams at the extremes of high temperatures are outlined, with an emphasis on prospective studies related to nuclear astrophysics and astroparticle physics. Some of the experimental setups for nuclear structure, reaction, and astrophysics studies, which are available at ELI-NP, are described.

Nuclear reaction and structure studies using experimental facilities at Inter-University Accelerator Centre (IUAC)

Nuclear reaction and structure studies using experimental facilities at Inter-University Accelerator Centre (IUAC)

Dissipative Reactions with Intermediate-Energy Beams: A Novel Approach to Populate Complex-Structure States in Rare Isotopes.

A novel pathway for the formation of multiparticle-multihole excited states in rare isotopes is reported from highly energy- and momentum-dissipative inelastic-scattering events measured in reactions of an intermediate-energy beam of ^{38}Ca on a Be target. The negative-parity, complex-structure final states in ^{38}Ca are observed following the in-beam γ-ray spectroscopy of events in the ^{9}Be(^{38}Ca,^{38}Ca+γ)X reaction in which the scattered projectile loses longitudinal momentum of order Δp_{||}=700 MeV/c. The characteristics of the observed final states are discussed and found to be consistent with the formation of excited states involving the rearrangement of multiple nucleons in a single, highly energetic projectile-target collision. Unlike the far-less-dissipative, surface-grazing reactions usually exploited for the in-beam γ-ray spectroscopy of rare isotopes, these more energetic collisions appear to offer a practical pathway to nuclear-structure studies of more complex multiparticle configurations in rare isotopes-final states conventionally thought to be out of reach with high-luminosity fast-beam-induced reactions.

Nucleon momentum distributions from inclusive electron scattering with superscaling analysis

Nucleon momentum distributions are crucial windows to probe nuclear structures. They provide valuable information not only on mean-field structures but also on short-range correlations. The $y$ scaling analysis generally serves as a tool to extract the nucleon momentum distribution from inclusive quasielastic electron cross sections. In this paper, we report new nucleon momentum distributions for deuteron, ${}^{3,4}\mathrm{He}$, $^{9}\mathrm{Be}$, and $^{12}\mathrm{C}$, extracted, based on ${\ensuremath{\psi}}^{\ensuremath{'}}$ scaling, directly from the latest high-precision experimental data. It is found that, for deuteron, ${}^{3,4}\mathrm{He}$, $^{9}\mathrm{Be}$, and $^{12}\mathrm{C}$, the ${\ensuremath{\psi}}^{\ensuremath{'}}$-scaling method provides reasonable results in agreement with state-of-the-art ab initio calculations up to 3.5 ${\mathrm{fm}}^{\ensuremath{-}1}$. These new nucleon momentum distributions can be helpful references for future studies of nuclear structures.

Production of polarized particle beams via ultraintense laser pulses

High-energy spin-polarized electron, positron, and $$\gamma$$ -photon beams have many significant applications in the study of material properties, nuclear structure, particle physics, and high-energy astrophysics. Thus, efficient production of such polarized beams attracts a broad spectrum of research interests. This is driven mainly by the rapid advancements in ultrashort and ultraintense laser technology. Currently, available laser pulses can achieve peak intensities in the range of $$10^{22}$$ – $$10^{23}$$ $$\hbox {Wcm}^{-2}$$ , with pulse durations of tens of femtoseconds. The dynamics of particles in laser fields of the available intensities is dominated by quantum electrodynamics (QED) and the interaction mechanisms have reached regimes spanned by nonlinear multiphoton absorption (strong-field QED processes). In strong-field QED processes, the scattering cross-sections obviously depend on the spin and polarization of the particles, and the spin-dependent photon emission and the radiation-reaction effects can be utilized to produce the polarized particles. An ultraintense laser-driven polarized particle source possesses the advantages of high brilliance and compactness, which could open the way for the unexplored aspects in a range of researches. In this work, we briefly review the seminal conclusions from the study of the polarization effects in strong-field QED processes, as well as the progress made by recent proposals for production of the polarized particles by laser–beam or laser–plasma interactions.

SO(3) quadratures in angular-momentum projection

While the angular-momentum projection is a common tool for theoretical nuclear structure studies, a large amount of computations are required particularly for triaxially deformed states. In the present work, we clarify the conditions of the exactness of quadratures in the projection method. For efficient computation, the Lebedev quadrature and spherical t-design are introduced to the angular-momentum projection. The accuracy of the quadratures is discussed in comparison with the conventional Gauss-Legendre and trapezoidal quadratures. We found that the Lebedev quadrature is the most efficient among them and the necessary number of sampling points for the quadrature, which is often proportional to the computation time, is reduced by a factor 2/3 in comparison with the conventional method.

Symplectic effective field theory for nuclear structure studies

A symplectic effective field theory that unveils the observed emergence of symplectic symmetry in atomic nuclei is advanced. Specifically, starting from a simple extension of the harmonic-oscillator Lagrangian, an effective field theory applied against symplectic basis states is shown to yield a Hamiltonian system with one fitted parameter. The scale of the system can be determined self-consistently as the ratio of the average volume of a nucleus assumed to be spherical to its volume as determined by the average number of oscillator quanta, which is stretched by the fact that the plane-wave solution satisfies the equations of motion at every order without the need for perturbative corrections. As an application of the theory, results for $^{20}\mathrm{Ne}$, $^{22}\mathrm{Ne}$, and $^{22}\mathrm{Mg}$ are presented that yield energy spectra, $B(E2)$ values, and matter radii in good agreement with experimentally measured results.