Low-energy Nuclear Physics Research Articles

Data reduction for low energy nuclear physics experiments using data frames

Low energy nuclear physics experiments are transitioning towards fully digital data acquisition systems. Realizing the gains in flexibility afforded by these systems relies on equally flexible data reduction techniques. In this paper, methods utilizing data frames and in-memory techniques to work with data, including data from self-triggering, digital data acquisition systems, are discussed within the context of a Python package, sauce. It is shown that data frame operations can encompass common analysis needs and allow interactive data analysis. Two event building techniques, dubbed referenced and referenceless event building, are shown to provide a means to transform raw list mode data into correlated multi-detector events. These techniques are demonstrated in the analysis of two example data sets.

Codebase release 2.0 for sauce

Low energy nuclear physics experiments are transitioning towards fully digital data acquisition systems. Realizing the gains in flexibility afforded by these systems relies on equally flexible data reduction techniques. In this paper, methods utilizing data frames and in-memory techniques to work with data, including data from self-triggering, digital data acquisition systems, are discussed within the context of a Python package, sauce. It is shown that data frame operations can encompass common analysis needs and allow interactive data analysis. Two event building techniques, dubbed referenced and referenceless event building, are shown to provide a means to transform raw list mode data into correlated multi-detector events. These techniques are demonstrated in the analysis of two example data sets.

Tracking Detectors in Low-Energy Nuclear Physics: An Overview

Advances in accelerator technology have enabled the use of exotic and intense radioactive ion beams. Enhancements to tracking detectors are necessary to accommodate increased particle rates. Recent advancements in digital electronics have led to the construction or planning of next-generation detectors. To conduct kinematically complete measurements, it is essential to track and detect all particles produced as a result of the reaction. Furthermore, the need for high-precision physics experiments has led to significant developments in the detector field. In recent years, highly efficient and highly granular tracking detectors have been developed. These detectors significantly enhance the physics programme at dedicated facilities. An overview of charged-particle tracking detectors in low-energy nuclear physics will be given.

Short-range expansion for the quantum many-body problem

In this work we derive a systematic short-range expansion of the many-body wave function. At leading order, the wave function is factorized to a zero-energy s-wave correlated pair and spectator particles, while terms that include energy derivatives and larger orbital angular momentum two-body functions appear at subleading orders. The validity of the expansion is tested for the two-body case, as well as the many-body case, where infinite neutron matter is considered. An accurate and consistent description of both coordinate-space two-body densities and the one-body momentum distribution is obtained. These results show the possibility to utilize such an expansion for describing different observables in strongly-interacting many-body systems, including nuclear, atomic and condensed-matter systems. This work also opens the path for a systematic description of large momentum transfer reactions in nuclear systems sensitive to short-range correlations, provides a link between such experiments and low-energy nuclear physics, and motivates measurement of new observables in these experiments.

Nuclear-matter saturation and symmetry energy within Δ -full chiral effective field theory

Nuclear saturation and the symmetry energy are key properties of low-energy nuclear physics that depend on fine details of the nuclear interaction. The equation of state around saturation is also an important anchor for extrapolations to higher densities and studies of neutron stars. Here we develop a unified statistical framework that uses realistic nuclear forces to link the theoretical modeling of finite nuclei and infinite nuclear matter. We construct fast and accurate emulators for nuclear-matter observables and employ an iterative history-matching approach to explore and reduce the enormous parameter domain of Δ-full chiral interactions. We perform rigorous uncertainty quantification and find that model calibration including O16 observables gives saturation predictions that are more precise than those that only use few-body data. Published by the American Physical Society 2024

α-Particle Transport Test of Korea Broad Acceptance Recoil Spectrometer and Apparatus at RAON

KoBRA of RAON has been prepared for various low energy nuclear physics studies such as nuclear structure, reactions, and astrophysics. An α-particle transport test was performed using a standard α-source of 241Am so as to examine the design parameters. The position distribution of the α-particles was measured with a PPAC at the dispersive and achromatic focal planes, and compared with that of a lise ++ Monte Carlo calculation. The results are consistent with each other, confirming a few design parameters. We report on the preliminary results of the α-particle transport test for KoBRA.

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.

Storage, accumulation and deceleration of secondary beams for nuclear astrophysics

Low-energy investigations on rare ion beams are often limited by the available intensity and purity of the ion species in focus. Here, we present the first application of a technique that combines in-flight production at relativistic energies with subsequent secondary beam storage, accumulation and finally deceleration to the energy of interest. Using the FRS and ESR facilities at GSI, this scheme was pioneered to provide a secondary beam of 118Te52+ for the measurement of nuclear proton-capture at energies of 6 and 7 MeV/u. The technique provided stored beam intensities of about 106 ions at high purity and brilliance, representing a major step towards low-energy nuclear physics studies using rare ion beams.

Wave-function-based emulation for nucleon-nucleon scattering in momentum space

Emulators for low-energy nuclear physics can provide fast & accurate predictions of bound-state and scattering observables for applications that require repeated calculations with different parameters, such as Bayesian uncertainty quantification. In this paper, we extend a scattering emulator based on the Kohn variational principle (KVP) to momentum space (including coupled channels) with arbitrary boundary conditions, which enable the mitigation of spurious singularities known as Kohn anomalies. We test it on a modern chiral nucleon-nucleon (NN) interaction, including emulation of the coupled channels. We provide comparisons between a Lippmann-Schwinger equation emulator and our KVP momentum-space emulator for a representative set of neutron-proton (np) scattering observables, and also introduce a quasi-spline-based approach for the KVP-based emulator. Our findings show that while there are some trade-offs between accuracy and speed, all three emulators perform well. Self-contained Jupyter notebooks that generate the results and figures in this paper are publicly available.

Recent progress in the construction of KoBRA for low-energy nuclear physics experiments

A multi-purpose experimental instrument, called as KoBRA (Korea Broad acceptance Recoil spectrometer and Apparatus), has been constructed for low-energy nuclear physics experiments at RAON (Rare Isotope Accelerator complex for ON-line experiments), and is being prepared in order to produce rare isotope beams at an energy of about 20 MeV/nucleon during the first beam commissioning phase. A test was performed to measure the positions of 4He ions at the dispersive and achromatic foci of KoBRA using an 241Am α-source placed at the production target position, so as to examine the momentum dispersion and ion beam transport. We report on the results of the test and the detailed design of KoBRA including ion optics, together with the status of detectors for particle identification of rare isotopes.

Quantum information in nucleon-nucleon scattering

Nucleon-nucleon scattering is a fundamental process in low-energy nuclear physics. Although its spin correlations have been studied intensively, few works take the perspective of quantum information science. In this work, I explore the quantum information aspects of spin correlations in the partially polarized neutron-proton scattering in the $S$ wave. It is found that the spin mutual information, entanglement and discord of the out-states, when averaged over the possible in-states, all vary in a similar way with respect to the relative momentum. The novel connection between emergent symmetry and spin entanglement found by a previous study [Phys. Rev. Lett. 122, 102001 (2019)] could then be extended naturally to spin correlations beyond entanglement.

Low-energy nuclear physics and global neutron star properties

We address the question of the role of low-energy nuclear physics data in constraining neutron star global properties, e.g., masses, radii, angular momentum, and tidal deformability, in the absence of a phase transition in dense matter. To do so, we assess the capacity of 415 relativistic mean field and nonrelativistic Skyrme-type interactions to reproduce the ground state binding energies, the charge radii, and the giant monopole resonances of a set of spherical nuclei. The interactions are classified according to their ability to describe these characteristics, and we show that a tight correlation between the symmetry energy and its slope is obtained provided that $N=Z$ and $N\ensuremath{\ne}Z$ nuclei are described with the same accuracy (mainly driven by the charge radius data). By additionally imposing the constraints from isobaric analog states and neutron skin radius in $^{208}\mathrm{Pb}$, we obtain the following estimates: ${E}_{\mathrm{sym},2}=31.8\ifmmode\pm\else\textpm\fi{}0.7$ MeV and ${L}_{\mathrm{sym},2}=58.1\ifmmode\pm\else\textpm\fi{}9.0$ MeV. We then analyze predictions of neutron star properties and we find that the $1.4{M}_{\ensuremath{\bigodot}}$ neutron star (NS) radius lies between 12 and 14 km for the ``better'' nuclear interactions. We show that (i) the better reproduction of low-energy nuclear physics data by the nuclear models only weakly impacts the global properties of canonical mass neutron stars and (ii) the experimental constraint on the symmetry energy is the most effective one for reducing the uncertainties in NS matter. However, since the density region where constraints are required are well above densities in finite nuclei, the largest uncertainty originates from the density dependence of the energy density functional (EDF), which remains largely unknown.

BUQEYE guide to projection-based emulators in nuclear physics

The BUQEYE collaboration (Bayesian Uncertainty Quantification: Errors in Your effective field theory) presents a pedagogical introduction to projection-based, reduced-order emulators for applications in low-energy nuclear physics. The term emulator refers here to a fast surrogate model capable of reliably approximating high-fidelity models. As the general tools employed by these emulators are not yet well-known in the nuclear physics community, we discuss variational and Galerkin projection methods, emphasize the benefits of offline-online decompositions, and explore how these concepts lead to emulators for bound and scattering systems that enable fast and accurate calculations using many different model parameter sets. We also point to future extensions and applications of these emulators for nuclear physics, guided by the mature field of model (order) reduction. All examples discussed here and more are available as interactive, open-source Python code so that practitioners can readily adapt projection-based emulators for their own work.

Outlook on software framework in low and intermediate energy nuclear physics

Over the past decades nuclear physics experiments have seen a drastic increase in complexity. With the arrival of second generation radioactive ion beam facilities all over the world, the run for exploring more and more exotic nuclei is raging. The low intensity of RI-beams requires more complex setup, larger solid angle coverage and detection of a wider variety of charged and neutral particles. Design, construction and operation of a variety of complex instruments used in such experiments require many software developments. The short lifetime of experimental setups and multiple combinations of instruments demand a strong methodology. As the community is shifting to this new paradigm, the quest for the optimum framework is becoming central in the field. In this outlook we will introduce the specificity of the nuclear physics community, technical needs of such frameworks, and give an overview of the existing ones, with an emphasize on the difficult balance between computing performances, versatility and integration with other frameworks.

Nuclear structure data obtained by the (nth,2γ) reaction

The determination of nuclear structure parameters such as gamma transitions, level scheme, nuclear level density and radiative strength functions is one of the most important tasks in low-energy nuclear physics. The two-step gamma cascades method based on detection of gamma coincidences following neutron capture, ie. the (n,2γ) reaction has been proven to give spectroscopic data and data concerning level density and radiative strength function. This method allows for the study of the dynamics of interaction and inter-transition between Fermi-and Bose-states of the nucleus near the neutron binding energy. There is an essential difference between these intranuclear processes from those in classical and high-temperature superfluidity, which is determined by a shape of the investigated nucleus, the nucleon parity in it, existence of nucleons of different types (protons and neutrons) etc. Two-step gamma cascades technique has so far been successfully applied for 45 nuclei in the mass region 28<A<200. Brief description of the method will be included here with examples from the recent research

Gamma-ray track reconstruction using graph neural networks

Since the advent of the new generation of germanium detector arrays for low-energy nuclear physics experiments utilizing gamma-ray tracking, the challenges associated with track-reconstruction methods have been extensively studied. In the present work an approach based on recent developments in machine learning was used to address the problem. Here, a graph neural network was constructed and trained on data simulated in Geant4 in order to attempt track reconstruction of gamma rays below 1 MeV in a spherical shell geometry of pure germanium. Using a thick-shell geometry, and simulated data without energy- and position uncertainties the network achieved a reconstruction rate above 80% for complete tracks, and a combined peak-to-total value of 85% for energy spectra with four discrete peaks. For data with added noise, i.e. finite resolution in interaction-point position and energy, the corresponding peak-to-total ratio dropped to 74%. The track reconstruction was stable across multiplicities 1–10 but showed an increased error frequency in the energy range between 50 keV and 250 keV. To specifically study the complication of gamma tracks lost by out-scattering from the detector volume, a thin-shell (9 cm thickness) geometry was used together with a modified version of the GNN framework. By letting the GNN code identify and discriminate the out-scatter events, an improvement of the P/T value from 66% to 75% was found for the packed, noisy data. For the sake of comparison the new GNN model with existing gamma-ray tracking methods, a separate instance of the network was trained on slightly higher energies (up to 1.5 MeV) and multiplicities (up to 15) to evaluate 1.332 MeV photon cascade data in terms of P/T and photo-peak efficiency. The results for this GNN data set, with P/T values at 85% for single tracks and 74% for multiplicity 15, show clear promise when compared to the existing tracking methods.

Nuclear properties with semilocal momentum-space regularized chiral interactions beyond N2LO

We present a comprehensive investigation of few-nucleon systems as well as light and medium-mass nuclei up to $A=48$ using the current Low Energy Nuclear Physics International Collaboration two-nucleon interactions in combination with the third-order (${\mathrm{N}}^{2}\mathrm{LO}$) three-nucleon forces. To address the systematic overbinding of nuclei starting from $A\ensuremath{\approx}10$ found in our earlier study utilizing the ${\mathrm{N}}^{2}\mathrm{LO}$ two- and three-nucleon forces, we take into account higher-order corrections to the two-nucleon potentials up through fifth order in chiral effective field theory. The resulting Hamiltonian can be completely determined using the $A=3$ binding energies and selected nucleon-deuteron cross sections as input. It is then shown to predict other nucleon-deuteron scattering observables and spectra of light $p$-shell nuclei, for which a detailed correlated truncation error analysis is performed, in agreement with experimental data. Moreover, the predicted ground state energies of nuclei in the oxygen isotopic chain from $^{14}\mathrm{O}$ to $^{26}\mathrm{O}$ as well as $^{40}\mathrm{Ca}$ and $^{48}\mathrm{Ca}$ show a remarkably good agreement with experimental values, given that the Hamiltonian is fixed completely from the $A\ensuremath{\le}3$ data, once the fourth-order (${\mathrm{N}}^{3}\mathrm{LO}$) corrections to the two-nucleon interactions are taken into account. On the other hand, the charge radii are found to be underpredicted by $\ensuremath{\approx}10%$ for the oxygen isotopes and by almost $20%$ for $^{40}\mathrm{Ca}$ and $^{48}\mathrm{Ca}$.

Nuclear Forces for Precision Nuclear Physics: A Collection of Perspectives

This is a collection of perspective pieces contributed by the participants of the Institute of Nuclear Theory's Program on Nuclear Physics for Precision Nuclear Physics which was held virtually from April 19 to May 7, 2021. The collection represents the reflections of a vibrant and engaged community of researchers on the status of theoretical research in low-energy nuclear physics, the challenges ahead, and new ideas and strategies to make progress in nuclear structure and reaction physics, effective field theory, lattice QCD, quantum information, and quantum computing. The contributed pieces solely reflect the perspectives of the respective authors and do not represent the viewpoints of the Institute for Nuclear theory or the organizers of the program.

Numerical Studies on Primary Ionization in TPC

Identification followed by directionality measurement using reconstruction of tracks is very crucial for studying the reaction vertex kinematics. In the field of low-energy nuclear physics, Active-Target Time Projection Chambers (AT-TPCs) can be used to study the nuclear reaction kinematics through tracking of the reaction products which is important for cross-section measurement. Ions produced in primary ionization by any charged particle along their track in the active gas volume of TPC can be utilized for track reconstruction with position-sensitive electron collection system placed inside an electric field. The TPC gas volume acts as the tracker of the reaction products and the target for the reaction with the incoming projectile simultaneously which is advantageous to conventional detector arrays. In this context, the design of the electric field in the drift volume of the TPC is an important criterion for precise tracking as the tracking capability of the TPC is strongly governed by the homogeneity of the electric field. Due to the lesser mobility of positive ions produced in primary ionization, their accumulation in the drift volume can distort the local electric field. In low-energy nuclear physics, this effect may be substantial due to the significant amount of ionization produced by the low-energy projectile and reaction products. Here we report the spatial information of primary space charges produced by cosmic muon and alpha particle obtained with geant4 [1] and Heed [2] simulation packages. We have used photo absorption and ionization physics lists in geant4 for the simulation and compared the results with that of the Heed. The simulation results for the change in pressure of gas volume will be reported. These results can be used for finding the distortion of the electric field due to the space charge in the drift region of the TPC which can be helpful for designing an AT-TPC for low-energy nuclear reaction experiments.

Development of Micro-Pattern Gaseous Detectors for Nuclear Reaction Studies

One of the frontiers of today’s nuclear physics research is the synthesis of Super Heavy Elements (SHE). Fusion-fission dynamics, namely the competition between quasi fission and fusion is one of the key challenges to optimize the SHE. To have an insight into the dynamics, one requires the study of fission fragment mass and angular distribution near barrier energies for heavy-ion induced fission reactions. Recent successful installation of linear accelerators in India offers a unique opportunity to study the dynamics of nuclear reactions and formation process of SHE. For the effective utilization of these current, as well as upcoming facilities, development of novel detectors to study reaction dynamics, formation process of SHE with heavier projectiles and higher beam energies is needed. Gaseous detectors have undergone a rapid improvement in terms of spatial, temporal and energy resolution, rate capability, radiation hardness, ion feedback etc., ushering in a new genre of micro-structured devices based on semi-conductor technology, commonly known as Micro-Pattern Gaseous Detectors (MPGDs). Although many of the MPGD structures were primarily developed for high-rate tracking of charged particles in high energy physics experiments, stability of operation, simplicity of construction and relatively low cost make these detectors suitable for other applications, such as low-energy nuclear physics experiments. The present activities encompass a detailed evaluation of the operational conditions of Micromesh-Multi Wire and THGEM-Multi Wire hybrid detector operated in low-pressure isobutane gas with a view to optimizing their use in the detection of charged particles and fission fragments.