Spectroscopy along flerovium decay chains. III. Details on experiment, analysis, Cn 282 , and spontaneous fission branches
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
SEARCH · Engineering Papers
Results for “Nuclear Structure”
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Optimization of the generator coordinate method with machine-learning techniques for nuclear spectra and neutrinoless double- β decay: Ridge regression for nuclei with axial deformation
The generator coordinate method (GCM) is an important tool of choice for modeling large-amplitude collective motion in atomic nuclei. The computational complexity of the GCM increases rapidly with the number of collective coordinates. It imposes a strong restriction on the applicability of the method. In this work, we propose a subspace-reduction algorithm that employs optimal statistical ML models as surrogates for exact quantum-number projection calculations for norm and Hamiltonian kernels. The model space of the original GCM is reduced to a subspace relevant for nuclear low energy spectra and the NME of ground state to ground state 0νββ decay based on the orthogonality condition (OC) and the energy-transition-orthogonality procedure (ENTROP), respectively. For simplicity, the polynomial ridge regression (RR) algorithm is used to learn the norm and Hamiltonian kernels of axially deformed configurations. The efficiency and accuracy of this algorithm are illustrated for 76 Ge and 76 Se by comparing results obtained using the optimal RR models to direct GCM calculations. The low-lying energy spectra of 76 Ge and 76 Se, as well as the 0νββ-decay NME between their ground states, are computed. Furthermore, the results show that the performance of the GCM+OC/ENTROP+RR is more robust than that of the GCM+RR alone, and the former can reproduce the results of the original GCM calculation accurately with a significantly reduced computational cost.
59 ≤ A ≤ 89↗
New measurement of double- β decays of Mo 100 to excited states of Ru 100 with the CUPID-Mo experiment
The CUPID-Mo experiment, located at Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of 20 Li 2 100 MoO 4 (LMO) calorimeters each equipped with a Ge light detector (LD) for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double beta decays of 100 Mo to the first 0 + and 2 + excited states of 100 Ru using the full CUPID-Mo exposure (2.71 kg yr of LMO). We measure the half-life of 2νββ decay to the $0^+_1$ state as $T^{2ν→0^+_1}_{1/2}$ = (7.5 ± 0.8 (stat.) $^{+0.4}_{-0.3}$ (syst.)) × 10 20 yr. The bolometric technique enables measurement of the electron energies as well as the gamma rays from nuclear de-excitation and this allows us to set new limits on the two-neutrino decay to the $2^+_1$ state of $T^{2ν→2^+_1}_{1/2}$ > 4.4×10 21 yr (90% c.i.) and on the neutrinoless modes of $T^{0ν→2^+_1}_{1/2}$ > 2.1×10 23 yr (90% c.i.), $T^{0ν→0^+_1}_{1/2}$ > 1.2 × 10 23 yr (90% c.i.). Information on the electrons spectral shape is obtained which allows us to make the first comparison of the single state (SSD) and higher state (HSD) 2νββ decay models for the $0^+_1$ excited state of 100 Ru.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Triaxiality and the nature of low-energy excitations in Ge 76
The deformation properties of the low-lying states in 76 Ge have been investigated following a safe energy Coulomb excitation measurement with the GRETINA tracking array and CHICO2 heavy-ion counter at the ATLAS accelerator facility at Argonne National Laboratory. A comprehensive set of transition and static E2 matrix elements were extracted from the measured differential Coulomb cross-sections, and compared with results of configuration interaction shell-model calculations and computations carried out within the framework of the generalized triaxial rotor model. The remarkable agreement between the calculated and experimental data supports a near-maximum triaxial deformation for the ground state of 76 Ge. Additionally, the degree of softness of the asymmetry in 76 Ge and 76 Se was investigated using rotational invariants generated from configuration interaction shell-model wave functions computed with the jj44b and JUN45 effective interactions. The resulting invariants are shown to be consistent with a stiff triaxial deformation in 76 Ge and a predominantly soft triaxial potential for 76 Se, in agreement with the conclusions of recent works by this collaboration.
59 ≤ A ≤ 89↗
Charge trapping correction and energy performance of the Majorana Demonstrator
P-type point contact (PPC) high-purity germanium detectors are an important technology in astroparticle and nuclear physics due to their superb energy resolution, low noise, and pulse shape discrimination capabilities. Analysis of data from the Majorana Demonstrator, a neutrinoless double-β decay experiment deploying PPC detectors enriched in 76 Ge, has led to several novel improvements in the analysis of PPC signals. Here, in this work we discuss charge trapping in PPC detectors and its effect on energy resolution. Small dislocations or impurities in the crystal lattice result in trapping of charge carriers from an ionization event of interest, attenuating the signal, and degrading the measured energy. We present a modified digital pole-zero correction to the signal energy estimation that counters the effects of charge trapping and improves the energy resolution of the Majorana Demonstrator by approximately 30 % to around 2.4 keV full width at half-maximum at 2039 keV, the 76 Ge Q value. An alternative approach achieving similar resolution enhancement is also presented.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of cosmic-ray muon spallation products in a xenon-loaded liquid scintillator with KamLAND
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Correlations between flow and transverse momentum in Xe + Xe and Pb + Pb collisions at the LHC with the ATLAS detector: A probe of the heavy-ion initial state and nuclear deformation
The correlations between flow harmonics v n for n = 2, 3, and 4 and mean transverse momentum [p T ] in 129 Xe + 129 Xe and 208 Pb + 208 Pb collisions at $\sqrt{s}$ = 5.44 and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are potentially sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from nonflow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and an event-activity selection based on particle production at very forward rapidity. The v n -[p T ] correlations show strong dependencies on centrality, harmonic number n, p T , and pseudorapidity range. Current models qualitatively describe the overall centralityand system-dependent trends but fail to quantitatively reproduce all features of the data. In central collisions, where models generally show good agreement, the v 2 -[p T ] correlations are sensitive to the triaxiality of the quadruple deformation. Comparison of the model with the Pb + Pb and Xe + Xe data confirms that the 129 Xe nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the 129 Xe nucleus from high-energy heavy-ion collisions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Quantifying resonance behavior in the fusion of O 17 with C 12 at above-barrier energies
Recent measurement of the fusion excitation function for 17 O + 12 C reported the significant suppression of the fusion cross section at E c.m. ≈ 14 MeV. This suppression was hypothesized to signal the existence of a 16 O + n + 12 C molecular configuration. Using the active-target detector MuSIC@Indiana provided an effective means of reexamining the fusion excitation function for 17 O + 12 C.The accuracy of this thick-target measurement is strengthened through comparison with the thin-target measurement of the excitation function for 17 F + 12 C. Furthermore, the result provides important information about the dependence of the average fusion cross section for the oxygen isotopic chain on neutron excess.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Coupled-cluster theory for strong entanglement in nuclei
Atomic nuclei can exhibit shape coexistence and multireference physics that enters in their ground states, and accurately capturing the ensuing correlations and entanglement is challenging. Here, we address this problem by applying single-reference coupled-cluster theory based on spherical and deformed reference states and the tailored coupled-cluster method. The latter combines configuration interactions to capture static correlations with coupled-cluster theory for dynamic correlations. We compute the atomic nuclei 12 C, 28 Si, and 56 Ni and find that the tailored coupled-cluster method and the single-reference approach based on a deformed Hartree-Fock state yield the most accurate results.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Semimicroscopic description of isoscalar giant multipole resonances in medium-mass closed-shell nuclei
Main properties of isoscalar giant multipole resonances (up to L=3), including L=0,and 2 overtones, in medium-mass closed-shell nuclei are described within the semimicroscopic particle-hole dispersive optical model. Further, main properties are characterized by the energy-averaged strength distribution, projected (one-body) transition density, and probabilities of direct one-nucleon decay. Calculation results obtained for characteristics of the mentioned resonances in the 48 Ca, 90 Zr, and 132 Sn nuclei are compared with available experimental data.
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Evidence of nonstatistical neutron emission following β decay near doubly magic Sn 132
Not Available
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𝛽−decay of neutron-rich 45 Cl located at the magic number 𝑁 = 28
Results from the β-decay study of 45 Cl, produced in the fragmentation of a 140-MeV/u 48 Ca beam, are presented. The half-life of 45 Cl is measured to be 513(36) ms. β – and β – 1n decay populate excited states in 45 Ar and 44 Ar, respectively, and decay schemes for both daughter nuclei are established based on γ-ray singles and γ-γ coincidence data. Comparison with shell-model calculations using the FSU interaction shows that the low-lying negative-parity states in 45 Ar are well described by single-neutron configurations near the Fermi surface, whereas positive-parity states require neutron excitations across the N = 20 shell gap, consistent with allowed Gamow–Teller decay from 45 Cl. The strong β-feeding to the 5/2 + state in 45 Ar supports a 3/2 + ground-state assignment for 45 Cl over 1/2 + . Furthermore, the high Q β – value enables population of 1p1h states above the neutron separation energy in 45 Ar, leading to positive-parity states in 44 Ar through neutron emission. Tentative spin-parity assignments for excited levels in 44 Ar are made for the first time based on comparison with shell-model predictions, and the 2978-keV level is identified as an excited 0 + state with a configuration distinct from the ground state.
39 ≤ A ≤ 58↗
Examination of decay heat measurements and their relevance for understanding the origin of the reactor antineutrino anomaly
Measurements of the decay energy released as a function of time following the thermal neutron induced fission of 235 U and 239,241 Pu were performed in the 1970s at Oak Ridge National Laboratory with the purpose of quantifying possible loss of coolant accident scenarios. The derivative of this decay energy with respect to time, known in technical parlance as decay heat, is mainly composed of two terms, that of the electrons produced together with antineutrinos in the $β$-minus decay of the neutron-rich fission products, and that of the $γ$ rays produced in the subsequent decay of excited nuclear levels. In this work we study if this extensive set of decay energy measurements can be used to assess the reactor antineutrino anomaly, that is, the approximately 5% deficit of electron antineutrinos produced by nuclear reactors, first deduced by Mention and collaborators in 2011, and observed by the major reactor antineutrino experiments since. Furthermore, with the assistance of nuclear databases, we are able to obtain the ratio of electron spectra under equilibrium conditions for 235 U to 239 Pu, in better agreement with the lower trend recently reported by Kopeikin and collaborators, as well as those for 235 U to 241 Pu and 241 Pu to 239 Pu, which do not agree well with those measured at the Institut Laue-Langevin in the 1980s. We conclude that a new experimental campaign is needed to measure the electron spectra utilizing a high resolution and signal-to-noise-ratio electron spectrometer and a highly precise fission normalization procedure.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
α decay of the neutron-deficient isotope At 190
The alpha decay of the neutron-deficient 190 At isotope was observed following the 103 Rh( 90 Zr, 3n) 190 At reaction at Argonne National Laboratory. The reaction products were separated from the beam using the Argonne Gas-Filled Analyzer and implanted into a double-sided Si strip detector. The spatial and temporal correlations between implanted nuclei and subsequent α decays towards the known daughter isotope 186 Bi were used to identify and characterize 190 At nuclei. In this paper, two possible decay scenarios are proposed for the 190 At → 186 Bi decay.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
α -cluster microscopic study of C 12 + C 12 fusion toward the zero energy limit
The carbon burning process is a fundamental step of stellar evolution and governs the synthesis of chemical elements important for the formation of life. In this work, we utilize the microscopic hybrid α cluster (HαC) model and an analytical approach, both in the framework of the Imaginary Time Method (ITM), to study the carbon fusion reaction towards zero energy. We obtain the values of the cross sections, astrophysical factors and correlate our results to collective motion. We also include a calculation for the 2 + carbon fusion and discuss a possible experimental investigation. Our results confirm direct experimental and theoretical results close to the barrier, while suggest possible 2 + mixtures in the indirect experimental data. Furthermore, our study offers an accurate view of the burning process in the somewhat unexplored low energy region.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
g 9/2 neutron strength in the N = 29 isotones and the 52 Cr(d,p) 53 Cr reaction
We performed a measurement of the 52 Cr(d,p) 53 Cr reaction at 16 MeV using the Florida State University Super-Enge Split-Pole Spectrograph (SE-SPS) and observed 26 states. While all of the states observed here had been seen in previous (d,p) experiments, we changed five L assignments from those reported previously and determined L values for nine states that had not had such assignments made previously. The g 9/2 neutron strength observed in 53 Cr in the present work and in the N = 29 isotones 49 Ca, 51 Ti, and 55 Fe via (d,p) reactions is much smaller than the sum rule for this strength. Most of the observed L = 4 strength in these nuclei is located in states near 4 MeV excitation energy. The remaining g 9/2 strength may be located in the continuum or may be fragmented among many bound states. A covariant density-functional theory calculation provides support for the hypothesis that the g 9/2 neutron orbit is unbound in 53 Cr. The (α, 3 He) reaction may provide a more sensitive probe for the missing g 9/2 neutron strength. Additionally, particle-γ coincidence experiments may help resolve some remaining questions in this nucleus.
39 ≤ A ≤ 58↗
Invariant-mass spectroscopy in projectile fragmentation reactions
The fragmentation of a projectile into a number of pieces can lead to the creation of many resonances in different nuclei. We discuss application of the invariant-mass method to the products from such reactions to find some of the most exotic resonances located furthest beyond the proton drip line. We show examples from fragmentation of a fast 13 O beam including the production of the newly identified 9 N resonance. In extracting resonance parameters from invariant-mass spectra, accurate estimates of the background from nonresonant prompt protons are needed. These prompt protons are correlated with the resonances due to long-range Coulomb interactions and will suppress events when resonance decay products and the prompt protons have small invariant masses. The shape of this background is especially important in determining the widths of wide resonances typically found at the edge of the chart of nuclides. An event-mixing recipe is proposed to describe this background, where the mixed events have reduced weighting for the smaller invariant masses to account for the effect of the Coulomb final-state interactions. The weighting is based on the measured correlations of heavier hydrogen isotopes with the resonances or the projectile residues. We also show that the relative magnitude of the background can be reduced in some cases by selecting events where the resonance decay products are accompanied by a deuteron or triton cluster. Here, the deuteron and triton clusters are largely not products of resonant decay and thus events with an accompanying cluster are associated with fewer background protons than events without them. The width of the 5/2¯ state in 9 C with the new background prescription was found to be consistent with the value obtained using proton elastic scattering on 8 B. Improved values for the widths of 10 C, 10,11 N, and 12 O resonances were also obtained using the new background prescription.
6 ≤ A ≤ 19↗
Influence of the symmetry energy on the nuclear binding energies and the neutron drip line position
A clear connection can be established between properties of nuclear matter and finite-nuclei observables, such as the correlation between the slope of the symmetry energy and the dipole polarizability, or between compressibility and the isoscalar monopole giant resonance excitation energy. Establishing a connection between realistic atomic nuclei and an idealized infinite nuclear matter leads to a better understanding of underlying physical mechanisms that govern nuclear dynamics. In this work, we aim to study the dependence of the binding energies and related quantities (e.g., location of drip lines, the total number of bound even-even nuclei) on the symmetry energy S 2 (ρ). The properties of finite nuclei are calculated by employing the relativistic Hartree-Bogoliubov model, assuming even-even axial and reflection symmetric nuclei. Calculations are performed by employing two families of relativistic energy density functionals, based on different effective Lagrangians, constrained to a specific symmetry energy at the saturation density J within the interval of 30–36 MeV. Nuclear binding energies and related quantities of bound nuclei are calculated between 8 ≤ Z ≤ 104 from the two-proton to the two-neutron drip line. As the neutron drip line is approached, the interactions with stiffer J tend to predict more bound nuclei, resulting in a systematic shift of the two-neutron drip line towards more neutron-rich nuclei. Consequentially, a correlation between the number of bound nuclei N nucl and S 2 (ρ) is established for a set of functionals constrained using the similar optimization procedures. Furthermore the direction of the relationship between the number of bound nuclei and the symmetry energy highly depends on the density under consideration.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗