A systematic analysis of the relationship between spontaneous fission and alpha-decay half-lives is performed for actinides and superheavy nuclei in the ground state. The ratio of logarithmic half-lives exhibits regular trends with nuclear mass and charge numbers, showing almost constant behavior at fixed neutron excess. Based on these systematics, a new semiempirical formula is proposed that relates spontaneous fission half-lives to alpha-decay half-lives and neutron excess. The formula contains only three fitted parameters and provides a unified description for nuclei of different parities without introducing separate hindrance factors. It reproduces experimental spontaneous fission half-lives with a mean absolute deviation of 0.94 orders of magnitude for the dataset of 78 nuclei. A detailed comparison of the predicted half-lives calculated using microscopic-macroscopic and self-consistent microscopic models, more complex empirical parametrizations, and the new formula is presented. The formula can be used to predict spontaneous fission half-lives and validate experimental data, and it provides a criterion to determine the dominant decay mode (alpha decay or spontaneous fission). The existence of a fundamental relationship between spontaneous fission and alpha-decay processes is discussed.
Potential energy surfaces of superheavy nuclei are investigated within the multidimensionally constrained relativistic mean-field model. The results are analyzed using the Strutinsky shell-correction method, with particular emphasis on 296Lv and isotopic chains of Z = 114 and Z = 120. The analysis reveals that triaxial degrees of freedom substantially reduce the barrier height along the triaxial fission pathway compared to the axial fission path in 296Lv. A steplike behavior emerges in proton shell corrections for Z = 114 isotopes, contrasting with the smoother patterns observed in Z = 120 isotopes, is attributed to the differences in the ground-state deformations. The observed correlation between fission-barrier maxima and shell-correction minima points to the shell closures at neutron numbers N = 172 and N = 184 at Z = 114 and 120.
We develop a self-consistent relativistic second random-phase approximation (RSRPA) based on a covariant energy density functional with density-dependent point-coupling interaction. The formalism extends the conventional simple configuration space composed of particle-hole transitions by including two-particle-two-hole (2p-2h) configurations through a generalized Thouless ansatz and a time-dependent variational principle. To ensure consistency with the underlying mean-field ground state and avoid the double counting of correlations, we implement the subtraction method, in which the static contribution is removed from the residual interaction. The first applications of the RSRPA include studies of isoscalar and isovector giant monopole (ISGMR and IVGMR) and quadrupole resonances (ISGQR and IVGQR) in 16O, which demonstrate the importance of 2p-2h couplings to describe the fragmentation of the transition strength and the stabilizing role of the subtraction method.
Background: With the recent progress in lifetime measurements, there has been strong experimental and theoretical interest in studying the evolution of the collectivity in the long Te isotopic chain. Purpose: The purpose of the present work is to investigate the structure of low-lying excited states in even-even Te nuclei as well as the nu h11/2 band in the odd-mass systems within the interacting boson model framework. Methods: A new open-source Python package is developed to evaluate the eigenvalues and eigenfunctions of a Hamiltonian which contains both the standard nd and essential for triaxial deformation and mixed symmetry effects. Results: Systematic calculations of low-spin yrast and nonyrast states in even-even 108-124Te and odd-even 109-125Te nuclei have been carried out using the newly developed Python package and compared with the neighboring Cd isotopes. From the resulting eigenfunctions, the reduced transition probabilities B(E2) are calculated and compared to adopted values. Due to the vibrational-like structure of the spectra of the Te nuclei, the Hamiltonian is dominated by the vibrational term, which is reflected in the B(E2) values. This alone does not explain the low B4/2 ratios observed in some Te nuclei. However, it is demonstrated via the contour plot that the B4/2 ratios can be highly sensitive to the higher-order terms of the Hamiltonian within specific parameter domains. Conclusions: We demonstrate that inclusion of higher-order interactions can provide a possible explanation of the anomaly observed in certain Te isotopes. The results highlight both the importance of extended IBM Hamiltonians and the utility of pyIBM as a modern computational tool for collective nuclear structure studies. Q & centerdot; Q terms as well as higher-order terms which could be studies
Background: Dynamical effects associated with the fusion of mass-symmetric systems remain a central topic of research in nuclear reaction studies. Over the past few decades, measurements of light-particle evaporation spectra and their deviations from standard statistical model predictions have been extensively employed to investigate these effects. Such indirect probes have indicated the presence of fusion hindrance, attributed to the non-fusion of higher angular momentum (l) states in fusion of symmetric systems. Further, more recent investigations have suggested that similar effects may also manifest in asymmetric systems particularly at higher values of excitation energies. Since the suppression of fusion at higher angular momenta suggests a corresponding reduction in the fusion cross sections for such systems, the measurement of fusion cross sections or spin distributions would give better insight into the possible fusion hindrance. However, such anomalies have not yet been explored using these probes. Purpose: Fusion cross sections have been used as a probe to investigate the influence of entrance-channel mass asymmetry on fusion dynamics, as well as to examine the possible suppression of fusion for higher angular momentum and the deviations of light-particle evaporation spectra from the standard statistical model predictions. Method: Evaporation-residue (ER) excitation function measurements have been carried out for the reactions 16O +64Zn and 32S +48Ti, both leading to the formation of the 80Sr compound nucleus. The experiments were performed using the Heavy Ion Reaction Analyzer spectrometer. The experimentally obtained fusion cross sections were compared with each other as well as with the predictions from time-dependent Hartree-Fock (TDHF) calculations. Furthermore, the measured fusion cross sections have been employed to interpret the light-particle evaporation spectra for these systems, as reported in the literature. Results: The experimentally obtained fusion cross sections for both systems show good agreement with each other on a reduced scale, and the measured data are reasonably well reproduced by TDHF calculations. The present investigation rules out the possibility of non-fusion of higher angular momentum (l) states in symmetric systems, contrary to earlier reports in the literature. However, the fusion timescales extracted from the TDHF calculations indicate a delay in the fusion process for both symmetric and asymmetric systems, suggesting the presence of dynamical effects. Conclusions: The measured ER cross sections in the spanned energy region are insensitive to dynamical effects. However, the delay in the fusion timescales as predicted by TDHF calculations indicates a possible existence of fusion hindrance. To explore the fusion hindrance for such systems, it may be important to measure the spin distribution of the populated compound nucleus at high excitation energies.
Low-energy dipole excitations in 166Er were investigated via nuclear resonance fluorescence using a quasimonoenergetic, linearly polarized photon beam produced at the High Intensity gamma-ray Source (HI gamma S) facility at Duke University. The parity of the excited states was determined from the azimuthal asymmetry in the intensities of resonantly scattered gamma rays with respect to the polarization plane of the incident beam. Electric and magnetic dipole strengths were extracted for excitation energies between 2.2 and 3.5 MeV. The results are interpreted in terms of the nuclear scissors mode by comparing with large-scale shell-model calculations based on the Quasiparticle Vacua Shell Model. In addition, the characteristics of the E1 excitations are examined in comparison with those of neighboring rare-earth nuclei to explore their relations to collective two-phonon excitations of octupole and gamma modes.
We investigate the production and suppression of short-lived K*(892) resonances in p+p and Ar+Sc collisions at CERN-SPS energies (root sNN = 8.8, 11.9, and 16.8 GeV) using the Ultrarelativistic Quantum Molecular dynamics (UrQMD) model. We present multiplicities, rapidity, and transverse momentum distributions, and analyze the K*/K yield ratios as a function of energy and centrality. We further estimate the time interval between chemical and kinetic freezeout using the experimental method. A detailed comparison with recent NA61/SHINE data demonstrates that the UrQMD model captures the essential features of resonance dynamics, although the very strong resonance suppression in central collisions observed in the data cannot be quantitatively reproduced.
Two isomers with K pi = 19/2+ at 1876 keV with a half-life of 21(1) ns, and K pi = 23/2- at 2159 keV with a half-life of 93(6) ns have been identified in 173W, the lightest tungsten isotope to exhibit this phenomenon. An unusually high number of 13 branches have been established in the decay of the K pi = 23/2- isomer. This decay is associated with transitions involving significantly higher degrees of K forbiddenness and is in sharp contrast with the usual preferential deexcitation through branches, which are less forbidden, as is evident for the K pi = 19/2+ state in 173W. The inclusion of K-mixing effects, arising from band crossings in the sequences to which decays with larger degrees of K forbiddenness are observed, can qualitatively account for this contrasting behavior. These results provide a striking illustration of the competition between K conservation and K mixing in the decay of such isomers.
The level structure of 209Po has been studied by in-beam gamma-ray spectroscopy with the 209Bi(6Li, alpha 2n)209Po reaction at beam energies of 28, 30, 34 MeV. The level scheme of 209Po is expanded by the gamma-gamma coincidence measurement, where 27 new transitions and 23 new levels are observed. The lifetimes of 13/2-, 17/2-, and 23/2+ states are obtained and are consistent with the previous work, while the one of the 13/2+ state is measured for the first time. A configuration-interaction-shell-model calculation is performed, and its results are compared with the experimental results for 209Po, with an emphasis on the coupling between the single valence neutron hole and the even-even core of 210Po. A systematic comparison of the 13/2+ state in N = 125 chain is also studied in the current work.
The intruder bands in Sn isotopes, built on the 2p-2h excitation across the Z = 50 proton shell gap, are well-known examples of shape coexistence near the neutron mid-shell region. Spectroscopic signatures for shape coexistence include enhanced E0 transitions between the 0+ band heads. However, the underlying shape coexistence and mixing has been unclear because lifetime information for the excited 0+ states was incomplete in 118Sn. We thus present here the first measurement of the 0+3 lifetime in 118Sn using the fast-timing technique following thermal-neutron capture. The observed enhancement in rho 2(E 0; 0+3 -> 0+2 ) of 150(30) milliunits provides compelling indications for multiple shape coexistence in 118Sn. Additionally, three distinct shapes in 116,118,120Sn naturally emerged in theoretical calculations based on the quantum-number-projected generator coordinate method employing a relativistic energy density functional.
Isomers have long been known to be important for astrophysical nucleosynthesis processes, yet they are often neglected in network calculations due to computational limitations or lack of data. "Astromers" are astrophysically metastable nuclear states that can greatly impact nucleosynthesis pathways. In this work we show that astromers further impact the time-dependent electromagnetic signal during heavy element nucleosynthesis. In an experiment performed at the National Superconducting Cyclotron Laboratory, three 9-decaying states of 70Cu (6-ground state, and two isomeric states: 3-and 1+) were produced. 9-feeding values were extracted from experimental spectra and compared to shell-model and QRPA + PVC calculations. Average y-ray energies from the 9-decay events were incorporated into simulations of heavy element nucleosynthesis and were found to exhibit different energy release profiles over time, which may impact, in aggregate, time-dependent observable signals.
High-precision lifetime measurements of the 4+1 and 6+1 states in 92Mo and 94Ru are performed following the 36Ar + 64Zn fusion-evaporation reaction, employing a novel delayed-gated LaBr3 triple-gamma coincidence method. The lifetime of 4+1 is determined to be 33(5) ps for 92Mo and 70(4) ps for 94Ru, respectively. Our data confirm the anomalous enhancement of B(E 2; 4+-* 2+) in 94Ru versus previously known suppression in 96Pd. Shell-model calculation in the f5 pg9 model space with the monopole-based universal interaction demonstrates that rescaling off-diagonal two-body matrix elements reproduces all the B(E 2; 4+-* 2+) strengths without perturbing the others such as B(E 2; 6+-* 4+) and B(E 2; 8+-* 6+), identifying the significant influence of cross-orbital off-diagonal matrix elements on B(E2) strengths as well as the underlying partial seniority symmetry breaking.
This paper presents the first measurement of the angle between different jet axes (denoted as Delta R-axis) in Pb-Pb collisions. The measurement is carried out in the 0-10% most-central events at root s(NN) = 5.02 TeV. Jets are assembled by clustering charged particles at midrapidity using the anti-kT algorithm with resolution parameters R = 0.2 and 0.4 and transverse momenta in the intervals 40 < p(T)(ch jet) < 140 GeV/c and 80 < p(T)(ch jet) < 140 GeV/c, respectively. Measurements at these low transverse momenta enhance the sensitivity to quark-gluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP suggests that the observed narrowing of the Pb-Pb distribution relative to pp can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements disfavor intrajet p(T) broadening as implemented in a simple model calculation with the Baier-Dokshitzer-Mueller-Peigne-Schiff formalism for energy loss in the QGP. The comparison of Pb-Pb and pp collisions shows sensitivity to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss.
This paper presents the first measurements of the azimuthal anisotropy coefficients vn, which quantify the nth-order Fourier modulation of charged-particle azimuthal distributions, for n = 2-4 in root s(NN) = 5.36 TeV O-16+ O-16 and Ne-20+ Ne-20 collisions recorded with the ATLAS detector at the CERN Large Hadron Collider in 2025. The v(n) coefficients are measured as a function of transverse momentum (p(T)), collision centrality, and event multiplicity. They are extracted using two complementary methods: two-particle correlations with a template-fit subtraction of short-range nonflow contributions, and four-particle subevent cumulants, which intrinsically suppress nonflow effects and provide sensitivity to flow fluctuations. The results show a clear hierarchy v(2) > v(3) > v(4) and a nonmonotonic dependence on p(T), reaching a maximum around 2 GeV, consistent with trends observed in heavy-ion collisions. Detailed comparisons between the two collision systems reveal an enhanced v(2) in central Ne-20+ Ne-20 collisions, consistent with theory expectations based on the predicted prolate deformation of neon nuclei, in contrast to the slightly tetrahedral structure predicted for oxygen. The four-particle cumulant results highlight strong event-by-event fluctuations and provide the greatest sensitivity to nuclear shape effects. These measurements can place new constraints on the initial geometry and the hydrodynamic response in light-ion collisions, offering valuable input for models of nuclear structure.
Background: The development of GenIV nuclear reactors will take advantage of fast neutrons. They will necessitate nuclear data of low uncertainties over a wide range of neutron energies, notably above 1 MeV. As far as 235U is concerned, current experimental data on average prompt neutron multiplicities (vprompt) of qualified uncertainties show some discrepancies and do not always cover the full incoming neutron energy range of interest. Purpose: Measure the average prompt neutron multiplicity in the 235U(n, f) reaction as a function of incoming neutron energy between 1 and 700 MeV. Methods: The double time-of-flight technique was used at the Los Alamos Neutron Science Center to measure incoming and prompt fission neutron energies. The data were measured relative to the very well-known 252Cf(sf) prompt fission neutron spectrum (PFNS) and vprompt Cf. The integral over the reconstructed PFNS energy and angle distributions in the 235U(n, f ) reaction provided vprompt. Results: vprompt was obtained between 1 and 700 MeV with uncertainties below 0.5% above neutron incoming energies of 3 MeV. There are discrepancies between the data and the evaluations JEFF 4.0, ENDF/B-VIII.1, and Conclusions: The results are the most precise measurements of vprompt in the 235U(n, f ) reaction so far and cover well the region of interest for nuclear applications between 1 and 25 MeV. In addition, the data are precise enough to highlight the impact of second-chance fission on the increase rate of vprompt as a function of the incoming neutron energy.
We report high-statistics measurements of fifth- and sixth-order factorial cumulants and cumulant ratios of (net-)proton multiplicity distributions in Au + Au collisions at root s(NN) = 7.7-27 GeV, using data from the STAR experiment collected during the Beam Energy Scan Phase II at RHIC. Protons and antiprotons are identified at midrapidity (vertical bar y vertical bar < 0.5) with transverse momentum 0.4 < p(T) < 2.0 GeV/c. The proton factorial cumulants kappa(4), kappa(5), and kappa(6) increase with order but exhibit no sign alternation within current uncertainties, offering no evidence for a two-component structure in the proton multiplicity distribution, as might be expected near a first-order phase transition. The cumulant ratios C-5/C-1 and C-6/C-2 fluctuate around zero in collisions at 0-40% centrality. The results are consistent with both the negative predictions from lattice QCD and the positive trends obtained from the ultrarelativistic quantum molecular dynamics (UrQMD) model. At root s(NN) greater than or similar to 27 GeV, the C-4/C-2 and C-5/C-1 results are compatible with predictions from lattice QCD, functional renormalization group (FRG), and hadron resonance gas (HRG) models, while UrQMD describes the data better at lower energies. These measurements place constraints on baryon number fluctuations and offer valuable insights into the QCD phase structure.
The kinetic-to-hydrodynamic crossover in the quark-gluon plasma is conventionally diagnosed by scale ratios such as the Knudsen and inverse Reynolds numbers, which are not metrical on the space of distributions. I equip the Denicol-Niemi-Moln & auml;r-Rischke (DNMR) 14-moment manifold with the Fisher-Rao metric-the local Hessian of the Kullback-Leibler divergence-and study the resulting Riemannian geometry for conformal Bjorken flow in the relaxation-time approximation. The equilibrium Fisher metric fixes the shear viscosity as eta = 4P tau R/5, identifying near-equilibrium transport as an equilibrium statistical quantity. The full geodesic distance exceeds its linearized approximation by 15-35% at moderate shear, quantifying where Navier-Stokes-type expansions under-resolve the state-space distance. The equilibrium Fisher-Rao Ricci scalar of the five-dimensional shear sector is computed exactly within the truncation to be R = -5/21; the negative sign identifies the equilibrium statistical manifold as locally hyperbolic in the Riemannian-geometry sense, which on a statistical model corresponds to diverging geodesic deviation between nearby moment states-a geometric statement about the truncated exponential family, not a prediction for physical relaxation rates. All results are obtained within the DNMR 14-moment truncation for conformal Bjorken flow; the equilibrium relations are closure independent within the truncation, and finite-shear quantities are properties of the Jaynes maximum-entropy completion.
In the context of the ongoing PUMA experiment (CERN), which investigates antiproton annihilation on atomic nuclei, we study the energy shifts and widths of hydrogenic states in the p & strns; + 3H and p & strns; + 3He systems by performing ab initio calculations. The scattering lengths and scattering volumes are first determined by solving the Faddeev-Yakubovsky equations in configuration space. The level shifts and widths of the corresponding p & strns; 3H and p & strns; 3He hydrogen-like states are then obtained using the Trueman formula. A pronounced model dependence associated with the nucleon-antinucleon interaction is observed for certain states. Finally, annihilation densities are computed from the four-body wave functions. Comparison with the nuclear density distributions indicates that the antiproton-nucleus annihilation is predominantly peripheral.
Based on the generalized reduced R-matrix theory, the R-matrix analysis code (RAC) program is employed to analyze all reaction channels associated with the 7Be system. The present calculations provide reliable evaluation data, which shows overall good agreement with available experimental measurements. Benefiting from the multichannel and multienergy fitting procedure, the resulting evaluation is internally self-consistent. The uncertainties of the evaluated cross sections and the covariance matrix are determined using the generalized least-squares method with rigorous uncertainty propagation theory. Compared with existing evaluated nuclear data libraries, the present evaluations are the most comprehensive for the 7Be system, effectively supplementing gaps in current evaluations. For the 6Li(p, 3He)4He reaction, the RAC analysis indicates that the resonance at Ep approximate to 1.8 MeV is predominantly associated with the 5/2-state of 7Be compound nucleus. In addition, the astrophysical S factor for the 3He(4He, gamma) 7Be reaction is calculated based on the present evaluation and the S34(0) is determined as 0.563+0.022-0.022 keV b . These results are significant for future updates of evaluated nuclear data libraries and have important implications for nuclear astrophysics and the nucleosynthesis studies. The present analysis also highlights the limitations of existing experimental data for the 7Be system and the need for further high-precision measurements.
