abstract

Since 1957, astrophysics and nuclear physics have been working together to understand the evolution and nucleosynthesis of stars in our Galaxy. Today, this collaboration appears renewed by the investigation of exotic phenomena observed by the multi-messenger astronomy. However, important and challenging puzzles remain to be solved also in classical nuclear astrophysics. This paper deals with three case studies in which the solution to stellar physics problems is found in the nuclear physics of the studied environments. In particular, the influence of the \(^{12}\mathrm {C}+{^{12}\mathrm {C}}\) fusion rate on the exploitability of supernova progenitors is discussed along with how the \(^{17}\mathrm {O}+p\) reaction rate can help establish the stellar origin of certain dusts, and how precise data on \(\beta \)-decay in stellar plasmas are crucial to understand the neutron capture nucleosynthesis.

abstract

Nuclear reactions among charged particles in stars take place at energies generally well below the Coulomb barrier, so its penetration factor exponentially suppresses the cross section down to values as small as few nanobarns or picobarns. Reaching astrophysical energies opens new challenges and calls for new approaches. In this work, the scope of nuclear astrophysics will be introduced and how experiments are usually conducted will be discussed. In particular, we will focus on the use of indirect methods as complementary approaches to direct measurements, introducing the asymptotic normalisation coefficient (ANC) technique and the Trojan Horse Method (THM), used to deduce the cross sections of reactions with photons and charged particles in the exit channel, respectively, with no need for extrapolation. Recent results of the application of the two methods will be exposed: the \(^6\mathrm {Li}({^3\mathrm {He}},d)^7\mathrm {Be}\) measurement used to deduced the ANCs of the \(^3\mathrm {He}+{^4\mathrm {He}}\to {^7\mathrm {Be}}\) and \(p+{^6\mathrm {Li}}\to {^7\mathrm {Be}}\) channels and the corresponding radiative capture cross sections. Then, the THM measurement of the \(^{27}\mathrm {Al}(p,\alpha )^{24}\mathrm {Mg}\) cross section through the \(^2\mathrm {H}(^{27}\mathrm {Al},\alpha {^{24}\mathrm {Mg}})n\) reaction will be reviewed, as well as the \(^{12}\mathrm {C}+{^{12}\mathrm {C}}\) fusion reaction cross section using \(^{14}\)N to transfer \(^{12}\)C and induce the reaction of astrophysical importance down to astrophysical energies. The indirect measurements made it possible to assess the occurrence of several resonances that are responsible for significant changes in the reaction rate at relevant temperatures.

abstract

The low-lying electric dipole strength in \(^{111-113,116-122,124}\)Sn was extracted with the Oslo method to systematically investigate the pygmy dipole resonance (PDR) and its evolution in Sn isotopes. The nuclear level densities (NLD) and the \(\gamma \)-ray strength functions (GSF) obtained from the Oslo data were used as inputs in the TALYS reaction code to produce radiative neutron-capture cross sections, Maxwellian-averaged cross sections, and rates relevant for the heavy-element nucleosynthesis. Despite a relatively small observed impact of the PDR, the experimentally extracted \(^{121,123}\)Sn(\(n,\gamma \)) \(^{122,124}\)Sn cross sections provide a notable reduction of a currently available theoretical uncertainty for the abundances of Sb isotopes in the i-process simulations.

abstract

We developed a self-consistent finite temperature relativistic quasiparticle random phase approximation (FT-RQRPA) to investigate the behavior of electromagnetic transitions at finite temperature in even–even nuclei. Our investigation focuses on the isotopic chain of \(^{40-60}\)Ca, exploring the behavior of electric dipole (E1) and magnetic dipole (M1) transitions within a temperature range from \(T= 0\) to 2 MeV. The analysis reveals that E1 giant resonance is moderately modified with temperature increase, and new low-energy transitions appear at higher temperatures, making a pronounced impact, particularly in neutron-rich nuclei. This emergence is attributed to the unblocking of transitions above the Fermi level due to thermal effects on single-particle states. Similarly, for M1 transitions, an interesting result is obtained for \(^{40,60}\)Ca nuclei at higher temperatures, i.e. , the appearance of M1 transitions, which are forbidden at zero temperature due to fully occupied (or fully vacant) spin–orbit partner states. Furthermore, for Ca isotopes, we observe a shift in M1 strength peaks towards lower energies, primarily attributed to the reduction of spin–orbit splitting energies and residual interactions. The significant temperature dependence observed in the E1 and M1 responses emphasizes their potential importance in the modeling of photon strength functions and their applications in nuclear reaction studies relevant to astrophysics.

abstract

We discuss the GUDE functionals which consist of pion exchanges derived from chiral effective field theory and a Skyrme-like part. Certain pion terms lead to significant improvements in the description of ground-state energies, indicating they might be useful ingredients for true ab initio energy density functionals. In addition, we present estimates of the statistical parameter uncertainties of the GUDE functionals.

abstract

Recently, \(B\)(E2,\(0^+_1 \rightarrow 2^+_1)\) transition strength has been measured in \(^{36}\)Ca and \(^{38}\)Ca. Surprisingly, the measured value in \(^{36}\)Ca: \(B\)(E2\(\uparrow ) = 131(20)\) \(e^2\)fm\(^4\), is significantly larger than in \(^{38}\)Ca, where \(B\)(E2\(\uparrow ) = 101(11)\) \(e^2\)fm\(^4\), whereas an opposite tendency of \(B\)(E2) values is seen in the mirror nuclei \(^{36}\)S and \(^{38}\)Ar. The resonance \(2^+_1\) in \(^{36}\)Ca lies 465 keV above the proton emission threshold and its description requires inclusion of the coupling to the continuum. In this work, we analyze \(B\)(E2\(\uparrow )\) values in \(^{36}\)Ca, \(^{36}\)S, \(^{38}\)Ca, and \(^{38}\)Ar using the real-energy continuum shell model, the so-called shell model embedded in the continuum, in the \((1s_{1/2}\, 0d_{3/2}\, 0f_{7/2}\, 1p_{3/2})\) model space with the monopole adjusted effective interaction ZBM-IO.

abstract

An iterative adiabatic time-dependent Hartree–Fock–Bogoliubov (ATDHFB) method is developed within the framework of the Skyrme density functional theory. The ATDHFB equation is solved iteratively to avoid explicitly calculating the stability matrix. The contribution of the time-odd mean fields to the ATDHF(B) moment of inertia is incorporated self-consistently, and the results are verified by comparing them with the dynamical cranking predictions. The inertia mass tensor is calculated with the density-derivative term evaluated by numerical differentiation.

abstract

Our recent fully self-consistent model, that starts from QRPA on top of Skyrme–Hartree–Fock–Bogoliubov (SHFB) and includes the coupling between quasiparticles and vibrations, is discussed. We highlight the significant improvement of the results with respect to simple QRPA, and we focus on the sensitivity to the choice of a specific Skyrme functional.

abstract

The neutrinoless double-beta decay (\(0\nu \beta \beta \)) nuclear matrix elements (NMEs) cannot be directly deduced from any experimental data, and their reliable calculation remains a significant challenge for the nuclear physics community. Advanced nuclear structure approaches have been developed and applied to evaluate nuclear transitions of experimental interest. However, the calculated values of \(0\nu \beta \beta \) NMEs still vary widely among different methods, affecting predictions of decay rates and constraints on various lepton violation parameters. The two-neutrino double-beta (\(2\nu \beta \beta \)) decay, which has been experimentally confirmed for eleven isotopes, plays a crucial role in testing nuclear structure models. In this context, we present the modified formalism of the Second Tamm–Dancoff Approximation (STDA) for the calculation of double-beta decay transitions. For \(2\nu \beta \beta \) of \({^{48}}\)Ca, the corresponding NMEs are calculated within the STDA, and their dependence on relevant nuclear structure parameters is investigated. Our findings indicate that a significant quenching of the axial-vector coupling constant is necessary to accurately reproduce the half-life of \(2\nu \beta \beta \) decay.

abstract

A new virtual access facility Theo4Exp provides a variety of computer codes for nuclear structure and reactions, accessible to researchers worldwide. The use of these codes is made simple by the adoption of clear interfaces and the implementation of graphical tools. Results can be easily transmitted, exchanged and compared. The EURO-LABS project, funded within the EC Horizon Europe program, has provided the appropriate framework and dedicated personnel to create this service.

abstract

The generation of angular momentum in the primary fission fragments is discussed on the basis of the nucleon exchange transport treatment. Such an analysis leads to the expectation that the wriggling mode (in which the fragments have mutually parallel spins that are perpendicular to the fission direction) is fully populated, while twisting (where the fragments spins are opposite along the fission direction) is unlikely to play a major role; bending (where the fragments have mutually antiparallel spins that are perpendicular to the fission direction) probably has some presence which increases with mass asymmetry and with lower fragment kinetic energies. It is also briefly discussed how measurements of collective E2 photons may reveal the relative presence of the various dinuclear spin modes.

abstract

This work presents the preliminary fragment distributions produced through transfer-induced fission with a \(^{232}\)Th beam, which has been accelerated for the first time at GANIL on a \(^{12}\)C target. The experimental setup is described, as well as a newly implemented technique based on Machine Learning aiming at improving the resolution. The fragment mass and charge distributions for fission of \(^{244}\)Cm and \(^{234}\)U at different excitation energies are shown to illustrate the capability of the setup and quality of the results.

abstract

The founding of an anomaly by A. Krasznahorkay and collaborators in the Internal Pair Creation (IPC) in \(^8\)Be triggered the worldwide effort to investigate this phenomenon. At the Laboratori Nazionali di Lengnaro (LNL-INFN), a new \( e^+e^-\) pair spectrometer was built, and the first experimental campaign was performed in 2023 and 2024. This work describes the methodology implemented to analyze the data collected, including the energy reconstruction of the \(e^+e^-\) and the relative angle at which they were emitted.

abstract

A new electron–positron pair spectrometer has been designed and constructed for the simultaneous measurement of the energy and angular correlations of \(e^+e^-\) pairs from internal pair creation processes (IPC) of energetic nuclear transitions. Experiments were carried out to validate the performance of the spectrometer using the \(e^+e^-\) pairs from M1 transitions in the \(^7\)Li(\(p,\gamma )^8\)Be and an E0 transition in the \(^{19}\)F(\(p,\alpha ,e^+e^-)^{16}\)O reaction. Comparison with Geant4 Monte Carlo simulations demonstrates that the angular correlations of \(e^+e^-\) pairs can be determined with sufficient resolution and efficiency between a correlation angle of \(40^\circ \) and \(180^\circ \) degrees.

abstract

The reduction of the experimental spectroscopic factors when compared to shell model calculations and its dependence on the binding energy asymmetry has puzzled researchers for more than a decade. As it is understood, short-range correlations among nucleons play an important role in this quenching. To shed more light on this topic, an experiment was performed at GANIL to determine the reduction factor \({R}_{\mathrm {S}}\) in \(^{10}\mathrm {Be}(d,t)^9\mathrm {Be}\), \(^{10}\mathrm {Be}(d,{^3\mathrm {He}})^9\mathrm {Li}\), and \(^{12}\mathrm {Be}(d,{^3\mathrm {He}})^{11}\mathrm {Li}\) pick-up reactions. This work reports on the preliminary spectroscopic factors that will be used to extract \({R}_{\mathrm {S}}\), as well as a comparison and reanalysis of previous datasets for pick-up on \(^{10}\)Be. An agreement between our results and previously published data has been found, along with strong indications of a reduction factor in line with available systematics.

abstract

This paper reports on new \(B\)(E2) values for \(^{36}\)Si and \(^{38}\)Si obtained by Coulomb excitation at GANIL during the LISE 2022 campaign. The results agree well with shell model calculations and confirm the increase in proton and neutron excitations in the neutron-rich Si isotopes towards \(N=28\). The experiment was performed in a “brochette” mode together with the ACTAR TPC to measure simultaneously inelastic proton scattering.

abstract

Data on the structure of sulphur isotopes close to the neutron drip-line are rather scarce. The excited states of the very neutron-rich \(^{46}\)S and \(^{47}\)S nuclei have been investigated by in-beam gamma-ray spectroscopy at the Radioactive Isotope Beam Factory at the RIKEN Nishina Center. After multi-nucleon knockout reactions on the liquid-hydrogen MINOS target, the \(2^{+}_{1}\rightarrow 0^{+}_{1}\) gamma transition of \(^{46}\)S, already reported in literature, has been confirmed. Additionally, two new gamma rays have been assigned to this isotope and one gamma line has been observed in \(^{47}\)S.

abstract

Four neutron capture experiments were carried out at the Institut Laue–Langevin (ILL), Grenoble, with the FIPPS \(\gamma \)-ray spectrometer, with the aim of performing a complete low-spin spectroscopy study of \(^{42,43,44,45}\)Ca isotopes. The goal of the project is to investigate the structure of Ca isotopes in the \(A\sim 40\)–48 mass region, focusing in particular on shape coexistence phenomena. Preliminary results on \(^{42}\)Ca are discussed here, for which more than 10 new levels and 100 new transitions were found. Angular correlation analysis was also carried out based on newly found transitions, in order to pin down the spin-parity values for a number of new levels.

abstract

Using the high flux of fast neutron beam provided at the Neutrons For Science (NFS) facility of GANIL-SPIRAL2, high-resolution \(\gamma \)-ray spectroscopy of nuclei produced in the (\(n,xn\)) reactions is performed with the EXOGAM HPGe array. The nuclei produced by the (\(n,2n\)) and (\(n,3n\)) channels of \(^{58}\)Ni are re-examined through prompt \(\gamma \)-ray spectroscopy in coincidence with fast neutrons to provide a comprehensive and possibly new description of its level schemes and excitation functions.

abstract

A novel combination of two CD-shaped double-sided silicon strip detectors (DSSD) with Gammasphere, Microball, Neutron Shell, and Fragment Mass Analyzer has been exploited at the Argonne Tandem Linac Accelerator System (ATLAS) facility at the Argonne National Laboratory during an experimental campaign aiming to study proton-unbound states in odd-\(Z\), \(N\lt Z\) nuclei beyond \(^{56}\)Ni. The addition of the highly-pixelated DSSDs to the setup has improved its sensitivity and selectivity for in-beam proton–\(\gamma \) coincidence spectroscopy. Proton tracking capabilities of the DSSD system have been utilized for the first time to follow the beam-spot location on the target, which refines the computation of recoil vectors and thus proton-line energy resolution. Moreover, the high granularity of the DSSD system made it sensitive to unambiguously distinguish evaporated deuterons from evaporated protons. This enables unprecedented deuteron–\(\gamma \) coincidence studies along the \(N=Z\) line.

abstract

A high-statistics \(\beta \)-decay experiment was conducted at the TRIUMF-ISAC facility using the \(8\pi \) \(\gamma \)-ray spectrometer and its ancillary detectors to study the low-spin structure of \(^{98}\)Zr. The analysis of \(\gamma \)–\(\gamma \) and \(e^-\)–\(\gamma \) coincidence data is presented. New measurements of \(\gamma \)-ray branching ratios and mixing ratios are reported for four \(J^{\pi } = 2^+\) states located above 2 MeV excitation energy in \(^{98}\)Zr. Based on these measurements, ratios of \(B\)(E2) values for transitions to lower-lying levels are determined, highlighting the preferential decay paths of these \(2^+\) states.

abstract

We have used the recoil distance Doppler-shift method to measure lifetimes of excited states in \(^{108}\mathrm {Ru}\), \(^{110}\mathrm {Ru}\), and \(^{112}\mathrm {Ru}\). Excited states in these nuclei were populated by fusion–fission reactions between a \(^{238}\)U beam and a \(^{9}\)Be target in an experiment at GANIL. Fission fragments were identified event by event in the VAMOS++ spectrometer, while \(\gamma \)-rays were detected by the Advanced Gamma Tracking Array (AGATA). The lifetimes in the ground state band are consistent with rotational structures and constant \(B\)(E2) values indicate that the deformation does not change significantly across the chain of studied ruthenium nuclei. Preliminary results for lifetimes of states in the \(\gamma \)-band indicate a well deformed triaxial shape with a \(\gamma \) parameter close to \(30^{\circ }\) in \(^{110}\mathrm {Ru}\), with a slight change towards oblate deformation in \(^{112}\mathrm {Ru}\).

abstract

The structure of the low-lying quadrupole bands in \(^{180}\)Hf and \(^{182}\)W is investigated with the use of a microscopically derived IBM-1 Hamiltonian. For each isotope, a potential energy curve is constructed from self-consistent mean-field calculations, employing a Skyrme energy density functional. The fermionic potential energy curve is subsequently mapped onto the corresponding bosonic one, thus leading to the derivation of the IBM-1 Hamiltonian parameters. These parameters are then used as inputs for the calculation of energy spectra and \(B\)(E2) transition strengths for the ground state and \(\gamma \) bands in the examined isotopes. The results are compared to experimental data, showing an overall good agreement. Potential future applications of this mapping method are also discussed.

abstract

In May 2022 at the GSI Darmstadt, Germany, a \(^{208}\)Pb beam at 1 GeV/\(u\) was used to populate neutron-rich fragmentation products at \(N\approx 126\). Fragmentation products were separated and implanted in AIDA Si stoppers, surrounded by eight newly developed DEGAS and two EUROBALL high-purity Ge detectors. Delayed \(\gamma \) emissions revealed isomeric decays in \(^{204}\)Pt, confirming previous findings. An isomeric half-life of \(160 \pm 30\) ns was measured for the \(10^+\) state, and a combined half-life of \(7.9 \pm 1.3\) \(\mu \)s for the \(5^-\) and \(7^-\) states. Additionally, approximately three times more \(^{203}\)Ir events were detected than in 2006, suggesting new insights into the most neutron-rich \(N=126\) nucleus studied so far. Studying these nuclei enhances understanding of nuclear structure and nuclear shell models, and supports refining r-process path predictions for astrophysical isotopes.

abstract

Fission shape isomers (SI) are poorly understood metastable states characterized by a second super-deformed potential energy minimum coexisting with normally-deformed states in the low-spin regime. Although many such isomers have been observed in the actinide region, our understanding of the states of the second minimum remains very limited. For most SIs, the only available information is their half-life, determined via their exclusive decay mode, delayed fission. However, the interesting possibility of a competing branch of \(\gamma \)-back decay towards normally-deformed states opens up as the number of protons decreases and the fission barrier becomes harder to penetrate, uranium isotopes being the heaviest candidates. In this context, two experiments were performed to study \(^{236f}\)U using the nu-Ball2/PARIS spectrometer at the ALTO facility of IJCLab. The nu-Ball2 setup consists of 24 High Purity Germanium (HPGe) Clovers and 64 phoswiches (LaBr\(_3\)/NaI) from the PARIS Collaboration are added to cover more than 90% of the total solid angle. Additionally, a Double-sided Silicon Stripped Detector (DSSD) was used to measure the energy of outgoing light-charged particles. The state-of-the-art fully digital FASTER electronics allowed triggerless data acquisition at high data rates. The selectivity of this setup enabled us to probe rare decays with sub-microbarn cross sections.

abstract

A campaign of Coulomb-excitation experiments to study the electromagnetic structure of \(^{110}\)Cd was performed using beams of \(^{14}\)N, \(^{32}\)S, and \(^{60}\)Ni. The use of various reaction partners enables disentangling the contributions of individual electromagnetic matrix elements involved in the excitation process, yielding, among others, a precise determination of the lifetime of the 2\(^+_2\) state in \(^{110}\)Cd.

abstract

Multinucleon transfer reactions were employed in a series of experiments at Legnaro National Laboratories of INFN and at the Tandem Laboratory of the Horia Hulubei National Institute in Bucharest. The main aim was to investigate the shape coexistence phenomenon in even–even Sn isotopes, with mass \(A=112\)–118, through lifetime measurements of excited \(0^+\) states. Recent Monte Carlo Shell Model (MCSM) calculations predict, in fact, the appearance of well-separated secondary minima in the potential energy surfaces of these Sn isotopes, corresponding to deformed, prolate configurations. In this contribution, details on the analysis procedure and preliminary results are discussed.

abstract

Recent SuperHeavy Element (SHE) discoveries involve only a few events. The assignment of their mass and charge relies on calculations of the excitation function for the reaction and the measurement of their alpha decay, with cross-bombardments as a consistency check. However, a systematic and undetected charged particle evaporation channel would change the assignment. So, while the elements with atomic numbers \(Z=113\), 115, 117, and 118 complete the seventh row of the periodic table of the chemical elements, there is no direct proof of their atomic number, \(Z\). X-rays are a fingerprint of the atomic number of a nucleus since the X-ray energy is proportional to the atomic charge \(Z\). Our objective is to improve the detection efficiency by a factor of ten at L X-ray energies and the intrinsic resolution by a factor of twenty compared to the current performance of SIRIUS. The proposed detection system will be capable of unambiguously identifying the atomic number of the newly discovered superheavy elements through L X-ray measurements.

abstract

We show that a vibrational interpretation and good U(5) symmetry are maintained for the majority of low-lying normal states in \(^{110,112,114,116}\)Cd isotopes, consistent with the empirical data. The observed deviations from this paradigm are properly treated by an interacting boson model Hamiltonian which breaks the U(5) symmetry in selected non-yrast states, while securing a weak mixing with coexisting SO(6)-like intruder states. The results demonstrate the relevance of the U(5) partial dynamical symmetry notion to this series of isotopes.

abstract

Besides the level scheme, absolute transition strengths between excited states yield fundamental information on nuclear structure and can be determined from level lifetimes. The recoil distance Doppler-shift (RDDS) technique is very valuable for the measurement of lifetimes in the picosecond range. During the last years, our group constructed several very compact plunger devices for RDDS experiments with \(\gamma \)-ray spectrometers coupled to charged particle detector arrays situated in the target chamber, and with dedicated setups for multinucleon transfer reactions where the plunger must be placed at the grazing angle of the reaction. Recent investigations have addressed the evolution of nuclear structure in neutron-deficient nuclei in the \(A=170\) mass region from yrast \(B\)(E2) values and are discussed in this article. For these investigations very small \(B_{4/2} = B(\mathrm {E2};4_1^+ \to 2_1^+)/B(\mathrm {E2};2_1^+ \to 0_1^+)\) ratios are of particular interest, which cannot be explained with standard collective models and which are not expected from the actual level schemes nor this far from closed shells. Here, we present our new work on \(^{168}\)W, \(^{172}\)Pt, and \(^{176}\)Pt, focus on this \(B\)(E2) anomaly, and include \(B\)(E2) values between higher yrast states for which experimental data have been sparse.

abstract

The investigation of pygmy dipole strength (PDS) provides crucial insights into low-energy dipole excitations that occur in neutron-rich nuclei and are also predicted in proton-rich systems. These excitations represent a unique mode of soft excitation predominantly driven by complex interplay of transitions involving weakly-bound neutrons but also with some proton contributions. Over the past years, diverse theoretical approaches ranging from macroscopic models to the shell model and nuclear energy density functional (EDF) theories have been employed to explore the characteristics and fragmentation of PDS. These studies have uncovered its dependence on the neutron excess and relationships with the key nuclear properties such as the symmetry energy and neutron skin thickness. The advances in theoretical understanding of PDS provided valuable guidance for experimental studies of exotic nuclei. This paper reviews major theoretical findings on PDS, emphasizing their relevance to nuclear structure and their implications for astrophysical phenomena.

abstract

In this contribution, we discuss selected results of calculations of E1 dipole response of \(sd\)-shell nuclei within the Configuration Interaction Shell Model framework. Systematic calculations within this approach were performed to provide results of interest for the PANDORA Collaboration and to deepen our understanding of the low-lying dipole strength in neutron-rich nuclei.

abstract

The high-energy \(\gamma \) rays from the Giant Dipole Resonance (GDR) decay of \(^{56,60,62}\mathrm {Ni}^{*}\) nuclei at finite temperature between approximately 1.5 and 2 MeV, produced in the \(^{32,34,36}\mathrm {S}+{^{24,26}\mathrm {Mg}}\) reactions at bombarding energies between 78 and 90 MeV, were measured. The experiment was then analyzed with a statistical model using a Monte Carlo approach. Some evidence is found within the analysis on the presence of an extra yield on the tail of the Giant Dipole Resonance which may be attributed to a Pygmy Dipole Resonance in an excited nucleus.

abstract

Measurements of the \(\gamma \) decay from states above the neutron threshold in \(^{120}\)Sn, \(^{62}\)Ni, and \(^{58}\)Ni were performed at the Cyclotron Centre Bronowice (CCB) in Kraków, Poland. The experiment on \(^{120}\)Sn aims to study the Isoscalar Giant Quadrupole Resonance (ISGQR): data on \(\gamma \) decay of the ISGQR are, in fact, scarce and refer to \(^{208}\)Pb only. To better understand this phenomenon, we chose to investigate another nucleus in a different mass region. The experiment on \(^{62}\)Ni and \(^{58}\)Ni, instead, is devoted to the investigation of the low-energy part of the E1 response, denoted as Pygmy Dipole Resonance (PDR), to better understand the systematic dependence on neutron excess in nickel isotopes. It is part of a campaign on PDR, including various complementary measurements carried out at different facilities. The paper will describe the performances and characteristics of the experimental setup together with the first near-line results for both experiments.

abstract

The Pygmy Dipole Resonance is an exotic excitation mode whose microscopic nature is not yet fully understood. By using different probes in inelastic scattering reactions, it is possible to obtain complementary information on the character of excited structures. For this reason, the very first study of the Pygmy Dipole Resonance using a neutron probe has been performed. The experiment, focused on the \(^{140}\)Ce nucleus, took place in 2022 at the NFS facility at GANIL-SPIRAL2. The PARIS and MONSTER arrays were used for the \(\gamma \)-ray and scattered neutron detection, respectively. As the first step of the analysis, the elastic and inelastic scattering channels on a \(^{\mathrm {nat}}\)C target were investigated with a focus on the well-known first \(2^+\) excited state of \(^{12}\)C. The obtained results validate the analysis procedure, which will be applied to investigate the Pygmy Dipole Resonance in \(^{140}\)Ce.

abstract

The ELIGANT instrumentation at ELI-NP is one of the main sets of instruments designed and constructed over the last decade for photonuclear physics around and above the neutron separation threshold developed for the \(\gamma \)-ray beams. The main goals of these setups include photo-neutron cross-sections and evaluation of \(\gamma \)-ray strength in the giant dipole resonance and pygmy dipole resonance regions. In this contribution, we will give an overview of the current status of ELI-NP, the Gamma Above Neutron Threshold programme in general, the scientific goals of giant dipole resonances, and \(\gamma \)-ray strength functions both at ELI-NP and within the role of complementary measurements.

abstract

Light-by-light scattering is a relatively new area of experimental physics. Our recent, theoretical research shows that studying two-photon measurements in regions with lower transverse momentum (\(p_{\mathrm {t},\gamma }\)) and invariant mass (\(M_{\gamma \gamma }\)) allows us to observe not only the main contribution of photon scattering, known as fermionic loops but also mechanisms like the VDM-Regge (double-photon hadronic fluctuation). In addition, diphoton measurements at low diphoton masses are crucial for studies of light-meson resonance contributions in \(\gamma \gamma \to \gamma \gamma \) scattering. We also focus on the interference between different contributions. For future experiments with the ALICE FoCal and ALICE-3 detectors, we have calculated background contamination and have explored possibilities to minimize their impact.

abstract

We explore extensively new, and also long-standing, but still unsolved, nuclear structure problems by using beyond-mean-field model, Subtracted Second Random Phase Approximation (SSRPA). Firstly, the similarity between the subtraction method of SSRPA and Lee–Suzuki similarity transformation is pointed out to get the physical background of the SSRPA model. Secondly, we study the spin–isospin and electric excitations including the couplings to two-particle–two-hole states and the tensor correlations. Our results give a new insight into the quenching the of Gamow–Teller (GT) sum rule strengths without introducing any adjustable parameters in the self-consistent microscopic calculations. We further apply the SSRPA model to the \(\beta \) decay half-lives of four semi-magic and magic nuclei, \(^{34}\rm Si\), \(^{68,78}\rm Ni\), and \(^{132}\rm Sn\). The inclusion of the two-particle–two-hole (\(2p\)–\(2h\)) configurations shifts low-lying GT states downwards. It leads to an increase of the \(\beta \) decay phase space, which ensures the half-lives of the four nuclei are finite and reduces the \(\beta \) decay half-lives dramatically. The effect of tensor interaction on the \(\beta \) decay half-life in the SSRPA model is also pointed out to change largely the half-lives by about one to two orders of magnitude with respect to the ones obtained without tensor force. The magnetic dipole transitions are also studied in the SSRPA model.

abstract

In recent years, several cases of nuclei presenting the so-called “\(B_{4/2}\) anomaly” have been observed in the neutron-deficient region close to \(Z=50\) and \(Z=82\). In the last region, the osmium isotopic chain is of particular interest, as three consecutive isotopes, \(^{168,169,170}\)Os, have shown the presence of this peculiar phenomenon. An experiment aimed at extending the study to \(^{167}\)Os was performed at the Accelerator Laboratory of the University of Jyväskylä, using a beam of \(^{78}\)Kr at 360 MeV impinging on a \(^{92}\)Mo target. Lifetimes of several low-lying states were measured using the Recoil-Distance Doppler Shift method. The preliminary analysis and the study of the influence of unobserved feeders are discussed.

abstract

Multiple chiral doublet bands with two different quasiparticle configurations have been identified in the negative-parity band structure of the \(^{104}\)Rh nucleus. Besides the previously reported chiral doublet, which belongs to the \({\pi }(1g_{9/2})^{-1}{\otimes }{\nu } (1h_{11/2})^1\) configuration, a new chiral-candidate band pair has been observed. Comparison of the experimental data with detailed theoretical calculations suggests that the newly observed band pair is also a chiral doublet based on the \(\pi (1g_{9/2})^{-1}\otimes \nu (1g_{7/2})^{-2}(1h_{11/2})^1\) configuration.

abstract

The level scheme of the neutron-rich \(^{87}\)Se isotope has been extended up to 2397 keV excitation energy. The isotope of interest was produced in a neutron-induced fission reaction of a \(^{235}\)U target at the Institut Laue-Langevin in Grenoble. During the analysis, six new gamma transitions were identified by employing multifold gamma-ray coincidence relationships, measured with the FIPPS array. Based on the gamma angular correlations technique, tentative spin-parity assignments have been proposed for the low-lying levels.

abstract

The integration of the modernized Recoil Filter Detector with the EAGLE gamma-ray spectrometer at the Heavy Ion Laboratory of the University of Warsaw (HIL UW) offers new opportunities to advance spectroscopic studies of deformed medium-mass nuclei at high spins. This setup is designed to improve sensitivity to gamma rays with high energies, which are typically subject to significant Doppler broadening due to the high recoil velocities of the emitting nuclei. Additionally, the upgraded system will enable the investigation of shape transitions in octupole-deformed thorium nuclei, where gamma-ray spectra are dominated by a significant background from competing processes, such as Coulomb excitation and prompt fission.

abstract

The generator coordinate method (GCM) is a well-known method to describe nuclear collective motions. In this method, one needs to specify a priori the relevant collective degrees of freedom as input of the method, based on empirical and/or phenomenological assumptions. Recently, we extended the GCM to include simultaneous optimization of both the basis Slater determinants and the weight factors based on the variational principle. This extension allows for the automatic optimization of the collective subspace. In this study, we apply the extended GCM to analyze \(^{20}\)Ne using the Skyrme interaction. We demonstrate that the optimized basis states correspond to excited states along a collective path, in contrast to the conventional GCM, which typically superposes only local ground states. We further calculate the low-lying excited states with the angular momentum projection and discuss the capabilities of the extended method.

abstract

In ultraperipheral heavy-ion collisions (UPCs) at the Large Hadron Collider (LHC), Pb nuclei are excited through interactions induced by strong electromagnetic fields. The expected excitation energy could reach hundreds MeV, which leads to the subsequent emission of various particles, including neutrons, protons, and alpha particles. To accurately describe deexcitation of nuclei, we have developed two novel approaches. The first method utilizes the Heavy Ion Phase Space Exploration (HIPSE) model to simulate pre-equilibrium emissions and to estimate the excitation energy of the remaining nucleus. Our second approach introduces a new technique for modeling the excitation energy of the nucleus. This method consists of a two-component function to represent the excitation energy distribution more precisely, accounting for the energy loss due to the interaction between photons and the quasi-deuteron. Both of these modeling techniques are integrated with the results produced by the GEMINI++ generator, which implements the Hauser–Feshbach formalism to simulate the statistical decay of excited nuclei. The alternative calculations are done with the EMPIRE platform. Using these approaches, we obtained the cross sections for the emission of neutrons, protons, and alpha particles resulting from UPC at the LHC. Our results were compared with the experimental data of the ALICE group on neutron and proton multiplicities.

abstract

The complete fusion (CF), incomplete fusion (ICF), and neutron transfer (\(1n\) stripping, \(2n\) stripping, and \(1n\) pickup) cross sections for the \(^{7}\mathrm {Li}+{^{205}\mathrm {Tl}}\) system were measured at energies around the Coulomb barrier by the online \(\gamma \)‑ray detection technique. The measured CF cross sections were found to be suppressed at above-barrier energies compared to the one-dimensional barrier penetration model (1DBPM) as well as coupled channel (CC) calculations. However, measured CF cross sections at below-barrier energies are found to be enhanced compared to 1DBPM and are in reasonable agreement with the CC calculations. The suppression observed in CF cross sections at above-barrier energies is found to be commensurate with the measured total ICF cross sections. Among ICF cross sections, \(t\)-capture is found to be dominant over \(\alpha \)-capture at all the measured energies. It is also observed that ICF is dominant at below-barrier, while CF dominates at above-barrier energies. Measured neutron transfer cross sections were compared with coupled reaction channel (CRC) calculations and found to be in agreement. The cumulative sum of all measured observables CF, ICF, and neutron transfer cross sections was found to agree with the estimated reaction cross sections.