arXiv subjects

T. Cap

Publications and source records attributed to T. Cap.

14 recordsLinked to original sources

arXiv2026

From Superfluid Coherence to High-$K$ Fragment Channels at Nuclear Scission

The origin of fission-fragment spin remains unresolved. For $^{236}$U fission, we combine deformation-dependent finite-temperature pairing with a multidimensional scission-spectrum analysis. Near the pairing-quenching boundary, pair breaking exposes near-Fermi high-$\Omega$ intruder orbitals and opens high-$K$ channels. The resulting maximum spectroscopic capacities range from a few to more than a dozen units of $\hbar$. Rapid neck rupture acts as a non-adiabatic projection freeze-out, where pairing serves as a dynamical gate: its critical attenuation does not generate angular momentum but allows existing high-$K$ projections to be retained diabatically as local fragment-$K$ components while total angular momentum remains conserved.

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arXiv2026

Comparative Study of Langevin and Random Walk Models for Nuclear Fission in the Overdamped Regime

We present a comparative study of Langevin dynamics and a Metropolis random walk model applied to thermal neutron-induced fission of $^{229}$Th, $^{235}$U, $^{239}$Pu, $^{245}$Cm, $^{249}$Cf, and $^{255}$Fm. Both methods are implemented within an identical four-dimensional Fourier-over-Spheroid framework, using potential energy surfaces derived from the macroscopic-microscopic model. We show that the Metropolis walk corresponds to the overdamped limit of the Langevin equations and confirm this correspondence numerically by Langevin calculations performed in the strongly damped regime and with quantum corrections to the random force switched off. Under these conditions, the two approaches produce essentially identical mass distributions for the lighter actinides. Systematic deviations develop for the heavier actinides, where the Langevin dynamics yields a non-negligible symmetric fission component absent in the random walk results. We trace this difference to the kinematic structure of the Metropolis sampling and to the residual inertial dynamics retained in the Langevin framework. A parallel comparison of Langevin calculations with and without the quantum-corrected effective temperature $T^*$ isolates the contribution of zero-point fluctuations and suggests that their standard phenomenological treatment may overestimate their impact in certain cases. Both approaches qualitatively reproduce the asymmetric peak positions and their systematic evolution across the actinide chain, while a common quantitative limitation -- the narrowness of the predicted distributions -- points to the role of higher-dimensional deformation modes not included in the present parametrization.

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arXiv2026

Survival of Pairing Correlations and Shell Effects at Scission in Finite-Temperature Nuclear Fission: Implications for Odd-Even Staggering

We investigate the finite-temperature evolution of microscopic free-energy corrections in nuclear fission, focusing on pairing and shell effects near scission. The analysis is based on a finite-temperature BCS treatment combined with the Strutinsky method and is performed for representative deformation points along the fission path. Both pairing and shell contributions exhibit regular thermal attenuation, but their deformation dependencies differ substantially. In particular, pairing remains strongly deformation-dependent in the scission region, and its free-energy contribution differs markedly between the constant and surface-dependent pairing-strength prescriptions. The shell correction near scission is also significant at low temperature and is progressively suppressed with increasing excitation energy. These results support the interpretation of odd-even staggering in fragment charge yields as a manifestation of pairing correlations surviving into the strongly deformed pre-scission configuration. They also show that pairing and shell effects should be treated separately in finite-temperature dynamical calculations, with distinct deformation- and temperature-dependent attenuation laws.

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arXiv2026

Sensitivity of Isotopic Fission Yields in Actinides to the Macroscopic Liquid-Drop Model: LSD vs ISOLDA

The impact of the macroscopic liquid-drop prescription on isotope-resolved fission-fragment yields in the actinide region is assessed by comparing two alternative parameterizations: the Lublin--Strasbourg Drop (LSD) model and the ISOscalar Liquid Drop Approximation (ISOLDA). The two prescriptions differ primarily in the treatment of isospin dependence in the volume and surface terms; in ISOLDA, an explicit dependence on the isospin square $T(T+1)$, where $T=|N-Z|/2$, is introduced in both coefficients. Using an identical set of fragment-yield observables and the same experimental reference (fission of $^{250}$Cf$^*$ at low and high energies), the propagation of the macroscopic-energy choice into the predicted yields is quantified in terms of (i) the location of the most probable post-neutron isotopes along elemental chains, (ii) the widths and asymmetries of the isotopic distributions, and (iii) the population of neighboring nuclides on the distribution tails. A comparable description of the gross properties of the isotopic yield pattern is obtained with both prescriptions, particularly for light and intermediate fragments, where peak positions and near-maximum curvatures are reproduced similarly. The most discriminating differences are found for heavy-fragment chains, for which the ridge location and isotopic centroids are rendered more sensitive to macroscopic isospin terms. Overall, a closer average agreement with the evaluated data is obtained with LSD, while the LSD--ISOLDA spread is shown to provide a practical estimate of the macroscopic-model uncertainty in isotope-resolved yields.

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arXiv2026

Isotope-Resolved Ba and Xe Yields in Actinide Fission and Correlated Heavy--Light Fragment Systematics

Isotope-resolved post-neutron fission yields in the Ba and Xe chains are calculated and benchmarked against evaluated reference data, with emphasis on element-resolved isotopic chains $Y(N_f)$ at fixed fragment charge $Z$ and on the consistency of heavy--light fragment correlations. Calculations are performed within a four-dimensional (4D) Langevin framework employing Fourier-over-Spheroid shape parametrization. The benchmark covers spontaneous fission of selected Cm and Cf isotopes (including $^{244,246}$Cm and $^{250}$Cf) as well as neutron-induced fission at thermal and 14-MeV energies for representative actinides in the Th--Pu region (including $^{229}$Th, $^{235}$U, $^{239}$Pu, and $^{249}$Cf). The dominant neutron-number maxima are reproduced for a large fraction of the isotopic chains considered, indicating that the mean charge partition and the average neutron content of the main fission channels are described consistently. A systematic residual discrepancy is observed in the isotopic widths: the calculated yields often fall off too rapidly on the distribution tails, producing distributions that are narrower than the evaluated data, most notably for heavy-fragment chains.

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arXiv2025

Static Fission Properties of Even-Even Actinides within the Warsaw Macroscopic-Microscopic Model Using Fourier-over-Spheroid Parameterization

A systematic study of fission barrier heights and static properties of even-even actinide nuclei from Th to Cf has been performed within the Warsaw macroscopic-microscopic model using the five-dimensional Fourier-over-Spheroid (FoS) shape parameterization. The use of a large deformation grid, containing about $1.3\times10^{8}$ points for each nucleus, allows for a refined and numerically complete exploration of the potential energy landscape without dividing the configuration space into subregions or applying interpolation. Barrier heights, extracted via the Immersion Water Flow method, show good agreement with empirical evaluations (including the new IAEA RIPL-4 dataset) with mean deviations below 1 MeV. Special attention is given to the long-debated third, hyperdeformed minimum. For Th isotopes, a shallow but distinct third well appears, whereas it's absent in heavier actinides (U, Pu).

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arXiv2022

The Fusion-by-Diffusion model as a tool to calculate cross sections for the production of superheavy nuclei

This article summarizes recent progress in our understanding of the reaction mechanisms leading to the formation of superheavy nuclei in cold and hot fusion reactions. Calculations are done within the Fusion-by-Diffusion (FBD) model using the new nuclear data tables by Jachimowicz et al. [At. Data Nucl. Data Tables 138, 101393 (2021)]. The synthesis reaction is treated in a standard way as a three-step process (i.e., capture, fusion, and survival). Each reaction step is analyzed separately. Model calculations are compared with selected experimental data on capture, fissionlike and fusion cross sections, fusion probabilities, and evaporation residue excitation functions. The role of the angular momentum in the fusion step is discussed in detail. A set of fusion excitation functions with corresponding fusion probabilities is provided for cold and hot synthesis reactions.

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arXiv2021

Diffusion as a possible mechanism controlling the production of superheavy nuclei in cold fusion reactions

The fusion probability for the production of superheavy nuclei in cold fusion reactions was investigated and compared with recent experimental results for $^{48}$Ca, $^{50}$Ti, and $^{54}$Cr incident on a $^{208}$Pb target. Calculations were performed within the fusion-by-diffusion model (FbD) using new nuclear data tables by Jachimowicz et al. It is shown that the experimental data could be well explained within the framework of the FbD model. The saturation of the fusion probability at bombarding energies above the interaction barrier is reproduced. It emerges naturally from the physical effect of the suppression of contributions of higher partial waves in fusion reactions and is related to the critical angular momentum. The role of the difference in values of the rotational energies in the fusion saddle point and contact (sticking) configuration of the projectile-target system is discussed.

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arXiv2018

How to produce new superheavy nuclei?

Existing experimental facilities limit the possibilities for discovery of new nuclides to those synthesized with cross sections above 100 fb, but the perspectives for future high current accelerators could lower this limit by two orders of magnitude. Therefore, in the present work excitation functions for fusion-$xn$ evaporation reaction channels induced not only by $^{48}Ca$ but also by heavier projectiles (usually leading to smaller cross sections) on actinide targets were calculated in the framework of the fusion-by-diffusion (FBD) model. For the first time, in this approach, channels in which a proton ($pxn$) or alpha particle ($\alpha$$xn$) is evaporated have been included in the first step of the deexcitation cascade. To calculate the synthesis cross sections entry data such as fission barriers, ground-state masses, deformations and shell effects of the superheavy nuclei calculated in a consistent way within the Warsaw macroscopic-microscopic model were used. The only adjustable parameter of the FBD model is the injection point distance $s_{inj}$ and the value determined in our previous analysis of experimental cross sections for the synthesis of superheavy nuclei of Z=114-118 has been used. Excitation functions for the synthesis of selected (cross section above a few fb) new superheavies in the range of atomic numbers 112-120 are presented. Observation of 21 new heaviest isotopes is predicted. A realistic discussion of the FBD model uncertainties is presented for the first time.

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arXiv2018

Isospin influence on dynamical production of Intermediate Mass Fragments at Fermi Energies

The Intermediate Mass Fragments emission probability from Projectile-Like Fragment break-up in semi-peripheral reactions has been measured in collisions of $^{124}$Xe projectiles with two different targets of $^{64}$Ni and $^{64}$Zn at the laboratory energy of 35 \amev. The two colliding systems differ only for the target atomic number Z and, consequently, for the Isospin $N/Z$ ratio. An enhancement of Intermediate Mass Fragments production for the neutron rich $^{64}$Ni target, with respect to the $^{64}$Zn, is found. In the case of one Intermediate Mass Fragment emission, the contributions of the dynamical and statistical emissions have been evaluated, showing that the increase of the effect above is due to an enhancement of the dynamical emission probability, especially for heavy IMFs (Z$\gtrsim$ 7). This proves an influence of the target Isospin on inducing the dynamical fragment production from Projectile-Like Fragment break-up. In addition, a comparison of the Xe+Ni,Zn results with the previously studied $^{112,124}Sn+^{58,64}Ni$ systems is discussed in order to investigate the influence of the projectile Isospin alone and to disentangle between Isospin effects against system-size effects on the emission probability. These comparisons suggest that the prompt-dynamical emission is mainly ruled by the $N/Z$ content of, both, projectile and target; for the cases here investigated, the influence of the system size on the dynamical emission probability can be excluded.

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arXiv2015

Freeze-out configuration properties in the 197Au + 197Au reaction at 23 AMeV

Data from the experiment on the 197Au + 197Au reaction at 23 AMeV are analyzed with an aim to find signatures of exotic nuclear configurations such as toroid-shaped objects. The experimental data are compared with predictions of the ETNA code dedicated to look for such configurations and with the QMD model. A novel criterion of selecting events possibly resulting from the formation of exotic freeze-out configurations, "the efficiency factor", is tested. Comparison between experimental data and model predictions may indicate for the formation of flat/toroidal nuclear systems.

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arXiv2013

Calculations of the cross sections for synthesis of new {293-296}118 isotopes in {249-252}Cf(48Ca,xn) reactions

A project of using a target consisting of the mixture of (249-252)Cf isotopes to be bombarded with the 48Ca beam, aimed to synthesize new isotopes of the heaviest known element Z = 118, is under way at the FLNR in Dubna. In the present work excitation functions for all the reactions: 249Cf(48Ca,xn)(297-x)118, 250Cf(48Ca,xn)(298-x)118, 251Cf(48Ca,xn)(299-x)118 and 252Cf(48Ca,xn)(300-x)118 have been calculated in the framework of the fusion-by-diffusion model, assuming fission barriers, ground-state masses and shell effects of the superheavy nuclei predicted by Kowal et al. Energy dependence of the effective cross sections for the synthesis of selected new isotopes: (293)118, (294)118, (295)118 and (296)118 is predicted for the particular isotopic composition of the Cf target prepared for the Dubna experiment.

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arXiv2012

Correlations between emission timescale of fragments and isospin dynamics in $^{124}$Sn+$^{64}$Ni and $^{112}$Sn+$^{58}$Ni reactions at 35 AMeV

We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at mid-rapidity in semi-peripheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of $<$N/Z$>$ isospin asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in neutron to proton ratio $<$N/Z$>$ distributions than those produced in sequential statistical emission. All these effects support the concept of isospin "migration", that is sensitive to the density gradient between participant and quasi-spectator nuclear matter, in the so called neck fragmentation mechanism. By comparing the data to a Stochastic Mean Field (SMF) simulation we show that this method gives valuable constraints on the symmetry energy term of nuclear equation of state at subsaturation densities. An indication emerges for a linear density dependence of the symmetry energy.

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arXiv2012

Predictions of the FBD model for the synthesis cross sections of Z = 114-120 elements based on macroscopic-microscopic fission barriers

A complete set of existing data on hot fusion reactions leading to synthesis of superheavy nuclei of Z =114-118, obtained in a series of experiments in Dubna and later in GSI Darmstadt and LBNL Berkeley, was analyzed in terms of a new angular-momentum dependent version of the Fusion by Diffusion (FBD) model with fission barriers and ground-state masses taken from the Warsaw macroscopic-microscopic model (involving non-axial shapes) of Kowal et al. The only empirically adjustable parameter of the model, the injection-point distance (sinj), has been determined individually for all the reactions and very regular systematics of this parameter have been established. The regularity of the obtained sinj systematics indirectly points at the internal consistency of the whole set of fission barriers used in the calculations. Having fitted all the experimental excitation functions for elements Z = 114-118, the FBD model (with the new sinj systematics) was used to predict cross sections for synthesis of elements Z = 119 and 120. Regarding prospects to produce the new element Z = 119, our calculations prefer the 252Es(48Ca,xn)300-x119 reaction, for which the synthesis cross section of about 0.2 pb in 4n channel at Ec.m.= 220 MeV is expected. The most favorable reaction to synthesize the element Z = 120 turns out to be 249Cf(50Ti,xn)299-x120, but the predicted cross section for this reaction is only 6 fb (for 3n and 4n channels).

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