Nuclear Theory·nucl-th

Friday·May 24, 2024

19 papers—8 primary·11 cross-listed

01
[Submitted on 21 May 2024]
Prompt Fission Neutron Spectra of 233U(n,F)
V.M. Maslov
Prompt fission neutron spectra produced up to 20 MeV. Simultaneous analysis of measured and calculated data for 233U(n, F), 235U(n, F) and 239Pu(n, F) maintains stronger justification for the predicted PFNS of 233U(n, F). For the latter the reliable measured PFNS data are available at Eth only. Pre-fission neutron spectra influence the partitioning of fission energy between excitation energy and total kinetic energy of fission fragments. For the reactions 233U (n, F) and 235U (n, F) we have shown that the shape of PFNS depends on the fissility of composite and residual nuclei. The correlation of these peculiarities with contributions of (n, xnf) to the (n, F) and competition of (n, ng) and (n, xn) is established. Exclusive neutron spectra (n, xnf) are consistent with cross sections of 235U(n, F), 234U(n, F), 233U(n, F) and 232U(n,F) reactions, as well as neutron emissive spectra of 235U(n,xn) at 14 MeV. Initial model parameters for 233U (n,F) PFNS are fixed by description of prompt fission neutron spectra of 233U (nth, F). We predict the 233U(n,xnf) exclusive pre-fission neutron spectra of 233U(n,xn) reactions, total kinetic energy TKE of fission fragments and products, partials of average PFNS and observed PFNS of 233U(n,F). PFNS of 233U (n, F) are harder than those of 235U(n, F) PFNS, but softer than those of 239Pu(n, F). Difference of average energies of PFNS of 233U (n, F) and 235U(n, F) amounts to 1-3 %. At incident energies higher than (n, 2nf) reaction threshold the observed PFNS may seem similar, though the partial contributions of 233U(n,xnf) and 235U(n,xnf) are quite different. PFNS of 233U(n,xnf) are obtained in the energy range up to 20 MeV.
Comments:
32 pages, 23 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2405.13167 [pdf]
2 citations
02
[Submitted on 22 May 2024]
Universal separable structure of the optical potential
H. F. Arellano · G. Blanchon
Based on a momentum-space in-medium folding model, we disclose the universal separability of the optical potential, revealing its radial and nonlocality features at beam energies in the range 40 - 400 MeV and target mass numbers in the range $40 \leq A \leq 208$ . From this microscopic study we find that the nonlocality form factor is inherently complex and of hydrogenic nature, affecting both central and spin-orbit components of the potential. A striking outcome from this study is the consistent appearance of a nodal point in the imaginary radial form factor, notably suppressing surface absorption peaks, in evident contrast with Woods-Saxon's assumption of an absorptive peak at the nuclear surface. Our analysis reveals that the complex radial form factor can effectively be represented as convolutions of uniform spherical distribution with a Gaussian form factor and a Yukawa term. These robust microscopically-driven findings offer new ways for investigating nuclear reactions beyond the restricting Woods-Saxon and Perey-Buck assumptions.
Comments:
8 pages, 9 figures, published in PRC. Minor corrections made to the text
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2405.13301 [pdf]
PRC(2024)·5 citations
03
[Submitted on 22 May 2024]
Induced Isotensor Interactions in Heavy-Ion Double-Charge-Exchange Reactions and the Role of Initial and Final State Interactions
Horst Lenske · Jessica Bellone · Danilo Gambacurta · José-Antonio Lay
The role of initial state (ISI) and final state (FSI) ion-ion interactions in heavy-ion double-charge-exchange (DCE) reactions $A (Z, N) \to A (Z \pm 2, N \mp 2)$ are studied for double single-charge-exchange (DSCE) reactions given by sequential actions of the isovector nucleon-nucleon (NN) T-matrix. In momentum representation, the second-order DSCE reaction amplitude is shown to be given in factorized form by projectile and target nuclear matrix elements and a reaction kernel containing ISI and FSI. Expanding the intermediate propagator in a Taylor series with respect to auxiliary energy allows us to perform the summation in the leading-order term over intermediate nuclear states in closure approximation. %Please ensure meaning has been retained - corrected HL. The nuclear matrix element attains a form given by the products of two-body interactions directly exciting the $n^{2} p^{- 2}$ and $p^{2} n^{- 2}$ DCE transitions in the projectile and the target nucleus, respectively. %Please ensure meaning has been retained - corrected HL. A surprising result is that the intermediate propagation induces correlations between the transition vertices, showing that DSCE reactions are a two-nucleon process that resembles a system of interacting spin-isospin dipoles. Transformation of the DSCE NN T-matrix interactions from the reaction theoretical t-channel form to the s-channel operator structure required for spectroscopic purposes is elaborated in detail, showing that, in general, a rich spectrum of spin scalar, spin vector and higher-rank spin tensor multipole transitions will contribute to a DSCE reaction. Similarities (and differences) to two-neutrino double-beta decay (DBD) are discussed. ISI/FSI distortion and absorption effects are illustrated in black sphere approximation and in an illustrative application to data.
Comments:
27 pages
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2405.13523 [pdf]
Universe(2024)·8 citations
04
[Submitted on 22 May 2024]
Initial energy-momentum to final flow: a general framework for heavy-ion collisions
Jefferson Sousa🇧🇷 · Jorge Noronha🇺🇸 · Matthew Luzum🇧🇷
The evolution of a relativistic heavy-ion collision is typically understood as a process that transmutes the initial geometry of the system into the final momentum distribution of observed hadrons, which can be described via a cumulant expansion of the initial distribution of energy density and is represented at leading order as the well-known eccentricity scaling of anisotropic flow. We extend this framework to include the contribution from initial momentum-space properties, as encoded in other components of the energy-momentum tensor. We confirm the validity of the framework in state-of-the-art hydrodynamic simulations of large and small systems. With this new framework, it is possible to separate the effects of early-time dynamics from those of final-state evolution, even in the case when the distribution of energy does not fully determine subsequent evolution, as for example, in small systems. Specifically, we answer the question of when and how azimuthal correlations from the initial state survive to the final state. In very small systems such as $p$ - $p$ , for example, initial momentum degrees of freedom dominate over energy. Thus, even if the system forms a quark-gluon plasma that is well described by hydrodynamics, the usual hydrodynamic picture of the transmutation of initial geometry to final momentum anisotropy is broken. Nevertheless, we show that the hydrodynamic response to the full energy-momentum tensor can be well understood in a similar manner as larger systems. Additionally, this framework elucidates the generic features of the system's evolution that are responsible for the impressive success of hydrodynamic simulations, but which may still hold even in cases where hydrodynamics is not applicable.
Comments:
10 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2405.13600 [pdf]
PRC(2024)·10 citations
05
[Submitted on 22 May 2024]
"Soft" interaction parameters setting in the extended quantum molecular dynamics model
Chen-Zhong Shi · Xiang-Zhou Cai · Bo-Song Huang · Yu-Gang Ma
The extended quantum molecular dynamics (EQMD) model is one of the few quantum molecular dynamics (QMD)-like transport approaches that can be used to study the effective clustering structure as well as heavily deformed nuclei in both ground state nuclei and nuclear reactions. However, there are only two parameter sets that lead to hard incompressibility for long times. The aim of the present work is to obtain a soft equation of state (EoS) in the EQMD model. In this context, we take the isoscalar giant monopole resonance (ISGMR), which is sensitive to the EoS, as an example to check our work. By introducing a kind of standard Skyrme energy density functional with different parameter sets, such as SkP, SkT1, and SKXce, whose incompressibility value ranges from 200 to 268 MeV, the ISGMR of $^{208}$ Pb and other nuclei are studied. When the SkP parameter sets are adopted, our new soft interaction in the EQMD model gives reasonable agreement with the experimental data in the heavy ion regime.
Comments:
10 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2405.13652 [pdf]
PRC(2024)·4 citations
06
[Submitted on 22 May 2024]
Isovector giant dipole resonance mode with an improved propagation approach in the framework of EQMD model
Chen-Zhong Shi · Xiang-Zhou Cai · De-Qing Fang · Yu-Gang Ma
The Extended Quantum Molecular Dynamics (EQMD) model is one of the few QMD-like transport approaches that can describe the $α$ -clustering structure with efficient computational power. However, compared to most QMD-like models, the choice of equation of state (EOS) for nuclear matter is very limited. In this work, a Monte Carlo integral method is employed to calculate the density integration with non-integer exponent. We demonstrate the superiority of our approach by studying the isovector giant dipole resonance (IVGDR). This improvement will be beneficial for the EQMD model to study more valuable effects for heavy ion collisions in the near future.
Comments:
10 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2405.13664 [pdf]
EPJA(2024)·2 citations
07
[Submitted on 22 May 2024]
Theory of Majorana-Type Heavy Ion Double Charge Exchange Reactions by Pion--Nucleon Isotensor Interactions
Horst Lenske🇩🇪 · Jessica Bellone🇮🇹 · Maria Colonna🇮🇹 · Danilo Gambacurta🇮🇹
The theory of heavy ion double charge exchange (DCE) reactions proceeding by effective rank-2 isotensor interactions is presented. Virtual pion--nucleon charge exchange interactions are investigated as the source for induced isotensor interactions, giving rise to the Majorana DCE (MDCE) reaction mechanism. MDCE is of a generic character, proceeding through pairs of complementary ( $π^{\pm}, π^{\mp}$ ) reactions in the projectile and target nucleus. The dynamics of the elementary processes is discussed, where the excitation of pion--nucleon resonances are of central importance. Investigations of initial and final state ion--ion interactions show that these effects are acting as vertex renormalizations. In closure approximation, well justified by the finite pion mass, the second-order transition matrix elements reduce to pion potentials and effective two-body isotensor DCE interactions, giving rise also to two-body correlations in either of the participating nuclei. Connections to neutrinoless Majorana double beta decay (MDBD) are elucidated at various levels of the dynamics, from the underlying fundamental electro-weak and QCD scales to the physical scales of nuclear MDBD and MDCE physics. It is pointed out that heavy ion MDCE reactions may also proceed by competing electro-weak charge exchange processes, leading to lepton MDCE by electrons, positrons, and neutrinos.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2405.13700 [pdf]
Universe(2024)·9 citations
08
[Submitted on 23 May 2024]
Multiplicity fluctuations and rapidity correlations in ultracentral proton-nucleus collisions
Rupam Samanta🇵🇱 · Jean-Yves Ollitrault🇫🇷
A collision between a proton and a heavy nucleus at ultrarelativistic energy creates particles whose rapidity distribution is asymmetric, with more particles emitted in the direction of the nucleus than in the direction of the proton. This asymmetry becomes more pronounced as the centrality estimator, defined from the energy deposited in a calorimeter, increases. We argue that for high-multiplicity collisions, the variation of the impact parameter plays a negligible role, and that the fluctuations of the multiplicity and of the centrality estimator are dominated by quantum fluctuations, whose probability distribution can be well approximated by a correlated gamma distribution. We show that this simple model reproduces existing data, and we make quantitative predictions for collisions in the $0 - 0.1%$ and $0 - 0.01%$ centrality windows. We argue that by repeating the same analysis with a different centrality estimator, one can obtain direct information about the rapidity decorrelation in particle production.
Comments:
8 pages, 5 figures, Published version
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2405.14671 [pdf]
PLB(2024)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE