The European Physical Journal A最新文献

This work presents an alternative methodology for computing potentials matrix elements within the Lagrange-mesh method in momentum space. The proposed approach extends the range of treatable potentials to include previously inaccessible cases, such as the Coulomb and linear interactions. It enables, in particular, an efficient and accurate treatment of the Cornell potential, which plays an important role in potential models for hadronic physics. The method is validated across a variety of systems, with special attention given to the representation of both momentum and position probability densities.

Accurate neutron capture cross sections are essential for the design and operation of fast reactors using MOX fuels. For (^{242})Pu, the Nuclear Energy Agency (NEA) recommends 8–12% accuracy in the fast energy region (2–500 keV), compared to the current uncertainty of 35%. Moreover, integral experiments and previous measurements suggest the evaluated (^{242})Pu(n,(gamma )) cross section is overestimated, particularly in the JEFF-3.3 library, which shows a 14% overestimation between 1 keV and 1 MeV. Recent measurements from LANSCE reported a 20–30% reduction in the 1–40 keV range relative to evaluations. To solve these discrepancies, the (^{242})Pu(n,(gamma )) cross section was measured from 1 to 600 keV at CERN n_TOF-EAR1 facility using a 95(4) mg (^{242})Pu target, enriched to 99.959%. Gamma rays from neutron capture were detected with an array of (hbox {C}_6hbox {D}_6) scintillators and a novel application of the Pulse Height Weighting Technique was employed. The resulting cross section presents a systematic uncertainty between 8 and 12%, reducing the current uncertainties of 35% and achieving the accuracy requested by the NEA. Analysis using FITACS produced average resonance parameters, consistent with the analysis of the resolved resonance region. Our data align well with Wisshak and Käeppeler, and are 10–14% lower than JEFF-3.3 in the 1–250 keV range, helping to achieve consistency with integral benchmarks. At higher energies, our results are in reasonable agreement with ENDF/B-VIII.1 and JEFF-3.3. In contrast, DANCE results appear to underestimate the cross section by a factor of 2–3 above a few keV.

A coupling scheme between a collective core, with quadrupole and octupole deformation, and a single-particle spin is proposed to describe the complex distribution of the negative and positive parity states in odd mass nuclei. The model is based on an axially symmetric quadrupole-octupole geometric Hamiltonian with an adjustable particle-core coupling, offering a wide range of spectroscopic structures. A specific instance of the model, involving a moderate coupling strength, is identified in (^{151})Ce, (^{153})Nd, (^{223})Ra and (^{225})Th nuclei, respectively discussed in terms of energy levels and relevant electric transitions.

The negative-parity dipole bands built on the (pi g^{-1}_{9/2} otimes nu h_{11/2}(g_{7/2}/d_{5/2}/d_{3/2}/s_{1/2})) configuration in neutron-rich Ag isotopes have been systematically investigated using the self-consistent tilted-axis cranking model within the frame of covariant density functional theory. The calculated energy spectra and the relation between spin and rotational frequency agree well with the available experimental data. The predicted deduced B(M1) strengths decreases with increasing spin, which is consistent with the characteristics of shears mechanism. The calculated deformation parameters show a shape evolution from slightly triaxial to small oblate deformation (near spherical) as the neutron number increases. The geometry of angular momenta further demonstrates that these dipole bands can be interpreted as stapler bands, in which the shears mechanism plays an increasingly important role in the structure of the stapler band in Ag isotopes as the neutron number increases.

A search for a shape isomer in (^{233})Th via delayed (gamma ) decay was performed using the Heidelberg–Darmstadt Crystal Ball spectrometer together with a (varDelta E)–E telescope for light charged particle identification. Excited states in (^{233})Th were populated through the (^{232})Th(d, p) reaction. The search for isomeric (gamma ) decay was based on a total-energy reconstruction method: prompt energy deficits (E_{textrm{Miss}}) indicated possible long-lived isomeric states. Corresponding delayed summed energies (E^{textrm{Sum}}_{textrm{del}}) were recorded with the Crystal Ball. A two-dimensional analysis of (E_{textrm{Miss}}) versus (E^{textrm{Sum}}_{textrm{del}}) was carried out for various prompt and delayed multiplicities and for delayed time intervals up to 200 ns within the excitation-energy range (E^{x} = 3)–7 MeV. No evidence of isomeric (gamma ) decay was observed. The branching ratio for the population of a potential shape isomer in the second minimum of (^{233})Th relative to the first minimum is constrained to ( < 10^{-6}), for isomeric states with energies (E^{x} = 2)–4 MeV and half-lives in the range (t_{1/2} = 2) ns–1 (mu )s. These results establish stringent experimental limits on the existence and population probability of a second minimum in the potential-energy surface of (^{233})Th, thereby providing valuable constraints for theoretical models of shape isomerism in actinide nuclei.

We introduce NuLattice, a Python software package for ab initio computations of atomic nuclei on lattices. The computational tools consist of Hartree Fock, the coupled cluster method, the in-medium similarity renormalization group, and full configuration interaction. At present, the employed interactions are from pion-less effective field theory at leading order and consist of two-body and three-body contacts. We present results for light nuclei (^{2})H, (^{3,4})He, (^{8})Be, (^{12})C, and (^{16})O. NuLattice algorithms exploit the sparsity and locality of lattice interactions, and as a result computations can be run on laptops.

We examine the nonsinglet distribution functions ((xu_v,xd_v)) using neural networks and genetic algorithms at the initial scale (Q^2_0). Evaluation of the distribution functions by the DGLAP equation can illuminate the nonsinglet distributions in a wide range of x and (Q^2) at the leading-order up to higher-order approximations. These results based on the neural networks and genetic algorithm are in good agreement with the CT18, MMHT14, MSHT20 and NNPDF4.0 parameterization groups.

Precise localisation of gamma-ray interactions is crucial for the performance of the Advanced GAmma Tracking Array (AGATA). The Pulse Shape Analysis (PSA) method used for the position estimation of gamma-ray interactions relies on a simulated signal database. The Pulse Shape Comparison Scanning (PSCS) method was used to scan AGATA crystals in order to produce an experimental database of signals. This paper presents a novel approach using Long Short-Term Memory (LSTM) neural networks to determine the 3D interaction position of gamma rays within AGATA crystals, trained on data from IPHC Strasbourg, allowing for the construction of an experimental database. A custom masked loss function is introduced to enable training with incomplete position information. The database generated by this new method outperforms the existing simulated database, and the experimental database obtained from the conventional PSCS algorithm.

The Advanced Plunger-Particle detector Array (APPA) is a new plunger device constructed to measure lifetimes of excited states in exotic nuclei, particularly those near the N = Z line. This instrument combines a compact plunger device with a charged-particle detector array to increase the experimental sensitivity for low-cross-section lifetime measurements employing fusion-evaporation reactions. APPA can be used in conjunction with the JUROGAM 3 germanium-detector array and with the RITU or MARA recoil separators available at the Accelerator Laboratory of the University of Jyväskylä (JYFL-ACCLAB). This article outlines the technical details of APPA, presents the lifetime measurement of the (2^+_1) state in ⁶²Zn, and reports the effect of APPA on the transmission efficiency of MARA and prompt (gamma )-ray and JYUTube detection efficiencies.