Intermediate Energy Heavy Ion Research Articles

Hot and dense QCD shear viscosity at (almost) NLO

The next-to-leading order weak-coupling shear viscosity of QCD was computed 6 years ago. However, these results have never been applied at finite baryon chemical potential μ, even though intermediate-energy heavy ion collisions and merging neutron stars may explore the Quark-Gluon Plasma in a regime where baryon chemical potentials are large. Here, we extend the next-to-leading order shear viscosity calculations to finite μ, and we show that, while the convergence of the weak-coupling expansion is questionable for achievable plasmas, it is somewhat better at μ > T than at μ = 0.

Isospin Correlations in Isotope Yields at Intermediate and High Energy Heavy-Ion Collisions

Isospin Correlations in Isotope Yields at Intermediate and High Energy Heavy-Ion Collisions

Quasi-monoenergetic heavy ion acceleration driven by sub-100 PW linearly polarized laser pulses in the radiation-dominated QED regime

Heavy ion acceleration from an ultrathin foil target irradiated by a p-polarized and spatially Gaussian laser pulse at intensity of 1023 W/cm2 is studied by using two-dimensional particle-in-cell simulations. We find that, in the extremely intense laser fields, the radiation reaction force from bright γ-rays radiated by radially oscillating electrons is large enough to match the Coulomb explosive force of foil electrons. The undesirable transverse expansion of the foil from the electron heating and inhomogeneous radial profile of the laser intensity is effectively suppressed. The foil maintains relatively good opacity in its central region stabilizing localized acceleration of heavy ions. With a laser of intensity 3.4 × 1023 W/cm2, duration of 33 fs, and power of 96 PW, a dense monoenergetic Au79+ ion bunch with a peak energy of ∼160 GeV can be obtained in the radiation-dominated QED regime. Such a high-quality heavy ion beam is useful for investigating nuclear matter equation of state and quantum chromodynamic phase transition in intermediate-energy heavy ion collisions.

Influence of Fragment Size on Isospin Effects in Transverse and Elliptic Flows and Nuclear Stopping in Intermediate Energy Heavy-Ion Collision

Influence of Fragment Size on Isospin Effects in Transverse and Elliptic Flows and Nuclear Stopping in Intermediate Energy Heavy-Ion Collision

In-medium effect and collective flow of pion production in intermediate energy heavy-ion collisions

In-medium effect and collective flow of pion production in intermediate energy heavy-ion collisions

Hot and dense QCD shear viscosity at leading log

The leading-order weak-coupling shear viscosity of QCD was computed almost 20 years ago, and the extension to next-to-leading order is 4 years old. But these results have never been applied at finite baryon chemical potential μ, despite the fact that intermediate-energy heavy ion collisions and merging neutron stars may explore the Quark-Gluon Plasma in a regime where baryon chemical potentials are large. Here we extend the leading-log shear viscosity calculation to finite μ, and we argue that the convergence of the weak-coupling expansion, while questionable for achievable plasmas, should be better at μ > T than at μ = 0.

Spectroscopy along flerovium decay chains. II. Fine structure in odd- A Fl289

Fifteen correlated α-decay chains starting from the odd-A superheavy nucleus Fl289 were observed following the fusion-evaporation reaction Ca48+Pu244. The results call for at least two parallel α-decay sequences starting from at least two different states of Fl289. This implies that close-lying levels in nuclei along these chains have quite different spin-parity assignments. Further, observed α-electron and α-photon coincidences, as well as the α-decay fine structure along the decay chains, suggest a change in the ground-state spin assignment between Cn285 and Ds281. Our experimental results, on the excited level structure of the heaviest odd-N nuclei to date, provide a direct testing ground for theory. This is illustrated by comparison with new nuclear structure calculations based on the symmetry-conserving configuration mixing theory.Received 12 April 2022Revised 1 September 2022Accepted 16 December 2022DOI:https://doi.org/10.1103/PhysRevC.107.L021301Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayLow & intermediate energy heavy-ion reactionsNuclear structure & decaysPropertiesA ≥ 220TechniquesNuclear density functional theoryNuclear Physics

Decay spectroscopy of Os171,172 and Ir171,172,174

We report on a study of the α-decay fine structure and the associated Eα−Eγ correlations in the decays of Os171,172 and Ir171,172,174. In total, 13 new α-decay energy lines have been resolved, and three new γ-ray transitions have been observed following the new decay branches to Re168 and W167. The weak α-decay branch from the bandhead of the νi13/2 band in Os171 observed in this work highlights an unusual competition between α, β, and electromagnetic decays from this isomeric state. The nucleus Os171 is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in Mo92(Kr83,xpyn) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyväskylä, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt γ-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that α-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus.5 MoreReceived 13 October 2022Accepted 11 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.014308Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayLow & intermediate energy heavy-ion reactionsNuclear structure & decaysProperties150 ≤ A ≤ 189Nuclear Physics

New isotope Mc286 produced in the Am243+Ca48 reaction

In this paper, we present results of the second experiment on the synthesis of Mc isotopes in the Am243+Ca48 reaction performed at the gas-filled separator DGFRS-2 of the SHE Factory at JINR. The new isotope Mc286 was synthesized, and its half-life of 20+98−9 ms and α-particle energy of 10.71±0.02 MeV were determined. A Mc286 α−decay chain was recorded down to the spontaneous fission of Db266. The spontaneous fission of Rg279 was observed for the first time in one of four new decay chains of Mc287. The excitation function of the reaction was measured at three Ca48 energies of 242, 250, and 259 MeV; the latter resulted in the first observation of the 5n−evaporation channel with a cross section of 0.5−0.4+1.3 pb. The decay properties of 21 previously known odd−Z isotopes were improved. The potential for an electron-capture decay mode is discussed for Mc288 and Nh284 isotopes. The half-lives of spontaneously fissioning nuclei produced in the Ca48−induced reactions with actinide targets are compared with several theoretical predictions.Received 10 October 2022Accepted 22 November 2022DOI:https://doi.org/10.1103/PhysRevC.106.064306©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayBeta decayFissionLow & intermediate energy heavy-ion reactionsNuclear fusionNuclear reactionsNuclear structure & decaysRare & new isotopesPropertiesA ≥ 220TechniquesSpectrometers & spectroscopic techniquesNuclear Physics

Evidence for spherical-oblate shape coexistence in Tc87

Excited states in the neutron-deficient nucleus Tc87 have been studied via the fusion-evaporation reaction Fe54(Ar36,2n1p)Tc87 at 115 MeV beam energy. The AGATA γ-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of γ rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc87 were identified by comparing γ-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in Tc87 is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.1 MoreReceived 10 September 2021Revised 24 January 2022Accepted 23 March 2022DOI:https://doi.org/10.1103/PhysRevC.106.034304Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectromagnetic transitionsLow & intermediate energy heavy-ion reactionsNuclear structure & decaysNucleon distributionTransfer reactionsProperties59 ≤ A ≤ 89Nuclear Physics

First results from the INDRA-FAZIA apparatus on isospin diffusion in Ni58,64+Ni58,64 systems at Fermi energies

An investigation of the isospin equilibration process in the reactions Ni58,64+Ni58,64 at two bombarding energies in the Fermi regime (32 and 52 MeV/nucleon) is presented. Data have been acquired during the first experimental campaign of the coupled INDRA-FAZIA apparatus in GANIL. Selecting from peripheral to semicentral collisions, both the neutron content of the quasiprojectile residue and that of the light ejectiles coming from the quasiprojectile evaporation have been used as probes of the dynamical process of isospin diffusion between projectile and target for the asymmetric systems. The isospin transport ratio technique has been employed. The relaxation of the initial isospin imbalance with increasing centrality has been clearly evidenced. The isospin equilibration appears stronger for the reactions at 32 MeV/nucleon, as expected due to the longer projectile-target interaction time than at 52 MeV/nucleon. Coherent indications of isospin equilibration come from the quasiprojectile residue characteristics and from particles ascribed to the quasiprojectile decay.6 MoreReceived 23 May 2022Accepted 26 July 2022DOI:https://doi.org/10.1103/PhysRevC.106.024603©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasEquations of state of nuclear matterLow & intermediate energy heavy-ion reactionsNuclear fragmentationNuclear reactionsTechniquesSpectrometers & spectroscopic techniquesNuclear Physics

Dynamical dipole excitation in the fission of a Ca40 + Sm152 composite system

The excitation of the dynamical dipole mode was explored in the formation of a heavy composite system with mass A≃ 190, by investigating its fission channel. The composite system was produced through the charge asymmetric reaction, Ca40 + Sm152, and the nearly charge symmetric one, Ca48 +Sm144, at Elab = 11 and 10.1 MeV/nucleon, respectively. High-energy γ rays and light charged particles were detected in coincidence with the two fission fragments by means of the MEDEA multidetector array coupled to two parallel plate avalanche counters. The kinetic energy spectra of the light charged particles measured at different angles were used to infer the average excitation energy, the average mass, and the average charge of the produced nuclei whereas the time of flight and the emission angle of the fragments were employed to reconstruct the fission dynamics. The study of the γ-ray spectra and angular distributions for the selected fission events, allowed us to establish (i) the excitation of the giant dipole resonance in the composite system of both reactions and (ii) the excitation of the dynamical dipole mode in the dinucleus of the charge asymmetric reaction by isolating its prompt γ radiation through the difference technique. The present results on the dynamical dipole mode were compared with the experimental findings for the evaporation channel of the Ca40 + Sm152 reaction and moreover with calculations based on a collective bremsstrahlung analysis of the reaction dynamics. Interesting hints connecting the dynamical dipole γ radiation with the superheavy element quest are given.10 MoreReceived 16 February 2022Accepted 6 June 2022DOI:https://doi.org/10.1103/PhysRevC.105.064611©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFissionLow & intermediate energy heavy-ion reactionsNuclear reactionsResonance reactionsNuclear Physics

Ionization yield measurement in a germanium CDMSlite detector using photo-neutron sources

Two photo-neutron sources, Y88Be9 and Sb124Be9, have been used to investigate the ionization yield of nuclear recoils in the CDMSlite germanium detectors by the SuperCDMS collaboration. This work evaluates the yield for nuclear recoil energies between 1 and 7 keV at a temperature of ∼ 50 mK. We use a geant4 simulation to model the neutron spectrum assuming a charge yield model that is a generalization of the standard Lindhard model and consists of two energy dependent parameters. We perform a likelihood analysis using the simulated neutron spectrum, modeled background, and experimental data to obtain the best fit values of the yield model. The ionization yield between recoil energies of 1 and 7 keV is shown to be significantly lower than predicted by the standard Lindhard model for germanium. There is a general lack of agreement among different experiments using a variety of techniques studying the low energy range of the nuclear recoil yield, which is most critical for interpretation of direct dark matter searches. This suggests complexity in the physical process that many direct detection experiments use to model their primary signal detection mechanism and highlights the need for further studies to clarify underlying systematic effects that have not been well understood up to this point.1 MoreReceived 15 February 2022Accepted 20 May 2022DOI:https://doi.org/10.1103/PhysRevD.105.122002© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectron-ion collisionsElectroweak interactions in nuclear physicsLow & intermediate energy heavy-ion reactionsParticle dark matterNuclear PhysicsGravitation, Cosmology & Astrophysics

O18 -induced single-nucleon transfer reactions on Ca40 at 15.3A MeV within a multichannel analysis

Background: Nucleon transfer reactions are selective tools for nuclear physics investigations. The theoretical and computational limits affecting in the past their data analysis could be nowadays surmounted thanks to the advent of methods with refined approximations and constraints, even when heavy-ion collisions are considered. Purpose: Modern microscopic calculations of heavy-ion-induced transfer reactions combined with precise experimental data offer the chance for accurately testing different reaction models as well as the nuclear structure description of the involved nuclear states. Method: Single proton and neutron transfer reactions were measured with the MAGNEX magnetic spectrometer for the O18+Ca40 system at 15.3A MeV. Excitation energy spectra and angular differential cross section distributions were extracted. The experimental results are compared with theoretical calculations performed in distorted wave and coupled channel Born approximation. The use of a coupled channel equivalent polarization potential to effectively describe the coupling effects affecting the initial state interaction is also considered. Spectroscopic amplitudes derived from a large-scale shell model with appropriate interactions adapted for the involved nuclei are employed. Results: Our theoretical calculations are in good agreement with experimental data, without the need for any scaling factor, validating the adopted reaction and nuclear structure parameters. Moreover, under the present experimental conditions, a weak dependence of the obtained results on the choice of the reaction models was observed. Conclusions: The good agreement between experimental and theoretical results validates the reliability of the parameter sets entering the calculations. They are extracted from or tested in complementary analyses of other reaction channels under the same experimental conditions. Such a multichannel approach represents the best option to pursue a solid, comprehensive, and model-independent description of the single-nucleon transfer reactions. The successful description of the present one-nucleon transfer data is also propaedeutic to the accurate assessment, under the same theoretical description, of higher-order transfer processes, like the sequential nucleon transfer mechanisms which are in competition with the direct charge exchange reactions.Received 14 September 2021Accepted 16 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.064609©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLow & intermediate energy heavy-ion reactionsModels & methods for nuclear reactionsTransfer reactionsTechniquesOptical, coupled-channel & distorted wave modelsNuclear Physics

Erratum: Effect of density and nucleon-nucleon potential on the fusion cross section within the relativistic mean field formalism [Phys. Rev. C 101 , 044603 (2020)

Received 3 May 2021DOI:https://doi.org/10.1103/PhysRevC.104.059901©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLow & intermediate energy heavy-ion reactionsNuclear fusionNucleon-nucleon interactionsPropertiesA ≥ 220Nuclear Physics

O18+Se76 elastic and inelastic scattering at 275 MeV

Background: An accurate description of the initial and final state interactions in the O18+Se76 collision is demanded by the NUMEN project. The study of single and double charge exchange nuclear reactions is the main purpose for NUMEN, since these can be used as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To date, the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for the NUMEN double charge exchange studies are poorly known. The O18+Se76 case, here under study, is particularly relevant due to its connection with the Ge76 neutrinoless double-β decay. Purpose: In this work the authors want to characterize the initial-state interaction for the O18+Se76 reactions at 275 MeV incident energy determining the optical potential and evaluating the effect of couplings with the inelastic scattering on the elastic channel. Methods: The angular distributions of differential cross section were measured in the angular region between 4∘ and 22∘ in the center-of-mass reference frame. The cross sections were compared with theoretical calculations, that adopt different optical potentials. Coupling effects on the elastic channel were determined into the coupled channels formalism. Results: The excitation energy spectrum of the colliding nuclei and the cross section angular distributions were measured with satisfactory energy resolution. The elastic scattering cross section is not well reproduced in the full angular range explored when the optical model approach is adopted. A good agreement is found using coupled channel calculations. The initial state interaction for the O18+Se76 nuclear reactions at 275 MeV is determined. Conclusions: Coupled channels effects are crucial to obtain a good description of the measured elastic and inelastic channels cross sections, even at large transferred momenta where the optical model approach fails in reproducing the experimental data. The role of channel coupling could be relevant also in the analysis of other open reaction channels in the same collision and should be accounted for in double charge exchange analyses as well.Received 19 December 2020Revised 6 October 2021Accepted 10 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.054610©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsLow & intermediate energy heavy-ion reactionsNuclear reactionsNuclear structure & decaysNucleon-nucleon interactionsTransfer reactionsProperties59 ≤ A ≤ 896 ≤ A ≤ 19TechniquesCollective modelsNuclear data analysis & compilationNuclear reaction analysisOptical, coupled-channel & distorted wave modelsSpectrometers & spectroscopic techniquesNuclear Physics

One-proton transfer reaction for the O18+Ti48 system at 275 MeV

Single-nucleon transfer reactions are processes that selectively probe single-particle components of the populated many-body nuclear states. In this context, recent efforts have been made to build a unified description of the rich nuclear spectroscopy accessible in heavy-ion collisions. An example of this multichannel approach is the study of the competition between successive nucleon transfer and charge exchange reactions, the latter being of particular interest in the context of single and double beta decay studies. To this extent, the one-proton pickup reaction Ti48(O18,F19)Sc47 at 275 MeV was measured for the first time, under the NUMEN experimental campaign. Differential cross-section angular distribution measurements for the F19 ejectiles were performed at INFN-LNS in Catania by using the MAGNEX large acceptance magnetic spectrometer. The data were analyzed within the distorted-wave and coupled-channels Born approximation frameworks. The initial and final-state interactions were described adopting the São Paulo potential, whereas the spectroscopic amplitudes for the projectile and target overlaps were derived from shell-model calculations. The theoretical cross sections are found to be in very good agreement with the experimental data, suggesting the validity of the optical potentials and the shell-model description of the involved nuclear states within the adopted model space.1 MoreReceived 27 May 2021Accepted 8 September 2021DOI:https://doi.org/10.1103/PhysRevC.104.034617©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsDouble beta decayLow & intermediate energy heavy-ion reactionsNuclear reactionsTransfer reactionsTechniquesOptical, coupled-channel & distorted wave modelsSpectrometers & spectroscopic techniquesNuclear Physics

Model independent reconstruction of impact parameter distributions for intermediate energy heavy ion collisions

We present a model independent method to reconstruct the impact parameter distributions of experimental data for intermediate energy heavy ion collisions, adapted from a recently proposed approach for ultra-relativistic heavy ion collisions. The method takes into account the fluctuations which are inherent to the relationship between any experimental observable and the impact parameter in this energy range. We apply the method to the very large dataset on heavy ion collisions in the energy range 20--100 MeV/nucleon obtained with the INDRA multidetector since 1993, for two observables which are the most commonly used for the estimation of impact parameters in this energy range. The mean impact parameters deduced with this new method for ``central'' collisions selected using typical observable cuts are shown to be significantly larger than those found when fluctuations are neglected, and as expected the difference increases as bombarding energy decreases. In addition, we will show that this new approach may provide previously inaccessible experimental constraints for transport models, such as an estimation of the extrapolated mean value of experimental observables for $b=0$ collisions. The ability to give more realistic, model independent estimations of the impact parameters associated with different experimental datasets should improve the pertinence of comparisons with transport model calculations which are essential to better constrain the equation of state of nuclear matter.

Erratum: Kinetic energy spectra and angular distributions of projectile-like fragments in C12,13+Nb93 reactions [Phys. Rev. C 102 , 024610 (2020)

Received 21 June 2021DOI:https://doi.org/10.1103/PhysRevC.104.039901©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLow & intermediate energy heavy-ion reactionsTransfer reactionsNuclear Physics

Elastic scattering and breakup reactions of the proton drip-line nucleus B8 on Pb208 at 238 MeV

Elastic scattering and breakup angular distributions of the weakly bound radioactive nucleus B8 on a Pb208 target at an incident energy of 238 MeV, which corresponds to four times the Coulomb barrier, have been measured at the HIRFL-RIBLL facility (Institute of Modern Physics, Lanzhou). The data have been analyzed using the optical model and the continuum discretized coupled channels (CDCC) formalism. The measured and calculated elastic scattering angular distributions do not show any significant Coulomb rainbow suppression. The angular distribution for the breakup reaction was measured for the first time at this energy. The angular distribution of the Be7 fragments could be reproduced considering elastic plus nonelastic breakup contributions, with the former evaluated with the CDCC calculations and the latter with the model of Ichimura, Austern, and Vincent [Phys. Rev. C 32, 431 (1985)]. The comparison of the breakup cross section of B8 with that of Be11 suggests that the Coulomb and centrifugal barriers encountered by the valence proton may suppress the breakup cross section.Received 25 October 2020Revised 9 December 2020Accepted 13 January 2021DOI:https://doi.org/10.1103/PhysRevC.103.024606©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBreakup reactionsDirect reactionsLow & intermediate energy heavy-ion reactionsNuclear reactionsUnstable nuclei induced nuclear reactionsTechniquesOptical, coupled-channel & distorted wave modelsNuclear Physics