Superfluid Model Research Articles

Simulation study of the proton-induced reaction cross sections for the production of 18F and 66–68Ga radioisotopes

The excitation functions of 18O(p,n) and 66–68Zn(p,xn) reactions were calculated using nuclear model based computer codes for the production of 18F and 66–68Ga radioisotopes. The model-based calculations, EMPIRE 3.2 Malta, ALICE/ASH and TALYS 1.8 nuclear reaction codes were used for obtaining the cross sections in the production of these radioisotopes. The nuclear reaction model results were compared to the existing experimental values, and TENDL-2015 data. It is generally accepted that the cross section predictions obtained using Superfluid model are preferable for the better description of experimental measurements.

Laszlo Tisza and the two-fluid model of superfluidity

Abstract The “two-fluid model” of superfluidity was first introduced by Laszlo Tisza in 1938. On that year, Tisza published the principles of his model as a brief note in Nature and two articles in French in the Comptes rendus de l'Academie des sciences, followed in 1940 by two other articles in French in the Journal de physique et le Radium. In 1941, the two-fluid model was reformulated by Lev Landau on a more rigorous basis. Successive experiments confirmed the revolutionary idea introduced by Tisza: superfluid helium is indeed a surprising mixture of two fluids with independent velocity fields. His prediction of the existence of heat waves, a consequence of his model, was also confirmed. Then, it took several decades for the superfluidity of liquid helium to be fully understood.

Engineering Weyl Superfluid in Ultracold Fermionic Gases by One-Dimensional Optical Superlattices

In this paper, we theoretically demonstrate by using one-dimensional superlattices to couple two-dimensional time-reversal-breaking gapped topological superfluid models, an anomalous Weyl superfluid (WS) can be obtained. This new phase features its unique Fermi arc states (FAS) on the surfaces. In the conventional WS, FAS exist only for a part of the line connecting the projections of Weyl points and extending to the border and/or center of surface Brillouin zone. But for the anomalous WS, FAS exist for the whole line. As a proof of principle, we self-consistently at the mean-field level claim the achievement of the anomalous WS in the model with a dichromatic superlattice. In addition, inversion symmetry and band inversion in this model are analyzed to provide the unique features of identifying the anomalous WS experimentally by the momentum-resolved radio-frequency spectroscopy.

Entrainment in Superfluid Neutron-Star Crusts: Hydrodynamic Description and Microscopic Origin

In spite of the absence of viscous drag, the neutron superfluid permeating the inner crust of a neutron star cannot flow freely, and is entrained by the nuclear lattice similarly to laboratory superfluid atomic gases in optical lattices. The role of entrainment on the neutron superfluid dynamics is reviewed. For this purpose, a minimal hydrodynamical model of superfluidity in neutron-star crusts is presented. This model relies on a fully four-dimensionally covariant action principle. The equivalence of this formulation with the more traditional approach is demonstrated. In addition, the different treatments of entrainment in terms of dynamical effective masses or superfluid density are clarified. The nuclear energy density functional theory employed for the calculations of all the necessary microscopic inputs is also reviewed, focusing on superfluid properties. In particular, the microscopic origin of entrainment and the different methods to estimate its importance are discussed.

Photon Induced Reaction Cross-Section Calculations of Several Structural Fusion Materials

In this paper; photo-neutron cross-sections have been computed for 27Al, 28,29Si, 52Cr, 54,56Fe isotopes by using nuclear reaction codes TALYS 1.6 and EMPIRE 3.1 with different level density models. Constant Temperature Fermi Gas, Back Shifted Fermi Gas and Generalized Superfluid Models have been employed from TALYS 1.6 whereas Generalized Super Fluid Model was the only model employed from EMPIRE 3.1 reaction codes. Obtained results have been analyzed with experimental values taken from the EXFOR database.

Phenomenological features of two-proton virtual decay of the 45Fe nucleus

On the basis of the theory of diagonal two-proton two-step virtual decays of spherical nuclei that was developed earlier and the superfluid model of the nucleus, the total and partial widths for the two-proton decay of the 45Fe parent nucleus in the ground state to the ground state of the 43Cr daughter nucleus were calculated along with the angular distribution of protons emitted in this decay. The calculated features of this mode of 45Fe decay were shown to be highly sensitive to the choice of form for nucleon shell potentials. It is also shown that there exists a potential such with which one can construct a successful simultaneous description of the experimental total width and the angular distribution of emitted protons for the aforementioned two-proton mode of decay of the 45Fe nucleus.

Pulsar glitch and nuclear EoS: Applicability of superfluid model

AbstractIn this contribution, we have made use of the contemporary equation of states (EOSs) for the complete neutron star structure, and confronted them with one particular glitch constrain for the crustal moment of inertia (MOI). We find that with these EOSs, the radii of three millisecond pulsars selected by NICER: PSR J0437-4715, PSR J1614-2230, PSR J0751+1807, are all around 12.5 km. Also, a star with M ≲ 1.55M⊙ would fulfill the MOI calculation for glitch constrain with the latest neutron superfluidity density, and the glitch crisis might not be present.

Towards High-Quality Visualization of Superfluid Vortices

Superfluidity is a special state of matter exhibiting macroscopic quantum phenomena and acting like a fluid with zero viscosity. In such a state, superfluid vortices exist as phase singularities of the model equation with unique distributions. This paper presents novel techniques to aid the visual understanding of superfluid vortices based on the state-of-the-art non-linear Klein-Gordon equation, which evolves a complex scalar field, giving rise to special vortex lattice/ring structures with dynamic vortex formation, reconnection, and Kelvin waves, etc. By formulating a numerical model with theoretical physicists in superfluid research, we obtain high-quality superfluid flow data sets without noise-like waves, suitable for vortex visualization. By further exploring superfluid vortex properties, we develop a new vortex identification and visualization method: a novel mechanism with velocity circulation to overcome phase singularity and an orthogonal-plane strategy to avoid ambiguity. Hence, our visualizations can help reveal various superfluid vortex structures and enable domain experts for related visual analysis, such as the steady vortex lattice/ring structures, dynamic vortex string interactions with reconnections and energy radiations, where the famous Kelvin waves and decaying vortex tangle were clearly observed. These visualizations have assisted physicists to verify the superfluid model, and further explore its dynamic behavior more intuitively.

The Deformation Structure of the Nuclei 32S and 36Ar

We applied two different approaches to investigate the deformation structures of the two nuclei S32 and Ar36 . In the first approach, we considered these nuclei as being deformed and have axes of symmetry. Accordingly, we calculated their moments of inertia by using the concept of the single-particle Schrödinger fluid as functions of the deformation parameter β. In this case we calculated also the electric quadrupole moments of the two nuclei by applying Nilsson model as functions of β. In the second approach, we used a strongly deformed nonaxial single-particle potential, depending on β and the nonaxiality parameter γ , to obtain the single-particle energies and wave functions. Accordingly, we calculated the quadrupole moments of S32 and Ar36 by filling the single-particle states corresponding to the ground- and the first excited states of these nuclei. The moments of inertia of S32 and Ar36 are then calculated by applying the nuclear superfluidity model. The obtained results are in good agreement with the corresponding experimental data.

Measurements of neutron capture cross sections on Zn70 at 0.96 and 1.69 MeV

The cross sections of the $^{70}\mathrm{Zn}(n,\ensuremath{\gamma})\phantom{\rule{0.28em}{0ex}}^{71}\mathrm{Zn}^{\mathrm{m}}\phantom{\rule{0.16em}{0ex}}({T}_{1/2}=3.96\ifmmode\pm\else\textpm\fi{}0.05\text{\ensuremath{-}}\mathrm{h})$ reaction have been measured relative to the $^{197}\mathrm{Au}(n,\ensuremath{\gamma})^{198}\mathrm{Au}$ cross sections at 0.96 and 1.69 MeV using a $^{7}\mathrm{Li}(p,n)\phantom{\rule{0.28em}{0ex}}^{7}\mathrm{Be}$ neutron source and activation technique. The cross section of this reaction has been measured for the first time in the MeV region. The new experimental cross sections have been compared with the theoretical prediction by talys-1.6 with various level-density models and $\ensuremath{\gamma}$-ray strength functions as well as the tendl-2015 library. The talys-1.6 calculation with the generalized superfluid level-density model and Kopecky-Uhl generalized Lorentzian $\ensuremath{\gamma}$-ray strength function predicted the new experimental cross sections at both incident energies. The $^{70}\mathrm{Zn}(n,\ensuremath{\gamma})\phantom{\rule{0.28em}{0ex}}^{71}\mathrm{Zn}^{\mathrm{g}+\mathrm{m}}$ total capture cross sections have also been derived by applying the evaluated isomeric ratios in the tendl-2015 library to the measured partial capture cross sections. The spectrum averaged total capture cross sections derived in the present paper agree well with the jendl-4.0 library at 0.96 MeV, whereas it lies between the tendl-2015 and the jendl-4.0 libraries at 1.69 MeV.

Investigation of excitation functions of proton-induced reactions on $^{94,\, 96,\, 98,\, 100}$Mo targets for production of radioisotopes $^{94m,\, 94g,\, 96m,\, 96g,\, 96,\, 99m}$Tc

In this work, we investigated the excitation functions of proton-induced reactions on even-even $^{94-100}$Mo isotopes for the production of medical radioisotopes $^{94m, 94g, 96m, 96g, 96, 99m}$Tc. To obtain the excitation functions we carried out cross-section calculations in the frameworks of the generalized superfluid model, microscopic level density model, and three options of the preequilibrium process in the Talys code. The aim of this study was to introduce a new aspect for the production of radioisotopes $^{94m, 94g, 96m, 96g, 96, 99m}$Tc with different models.

Modelling Neutron-induced Reactions on 232–237U from 10 keV up to 30 MeV

Comprehensive calculations of cross sections for neutron-induced reactions on 232–237U targets are performed in the 10 keV–30 MeV incident energy range with the code EMPIRE–3.2 Malta. The advanced modelling and consistent calculation scheme are aimed at improving our knowledge of the neutron scattering and emission cross sections, and to assess the consistency of available evaluated libraries for light uranium isotopes. The reaction model considers a dispersive optical potential (RIPL 2408) that couples from five (even targets) to nine (odd targets) levels of the ground-state rotational band, and a triple-humped fission barrier with absorption in the wells described within the optical model for fission. A modified Lorentzian model (MLO) of the radiative strength function and Enhanced Generalized Superfluid Model nuclear level densities are used in Hauser-Feschbach calculations of the compound-nuclear decay that include width fluctuation corrections. The starting values for the model parameters are retrieved from RIPL. Excellent agreement with available experimental data for neutron emission and fission is achieved, giving confidence that the quantities for which there is no experimental information are also accurately predicted. Deficiencies in existing evaluated libraries are highlighted.

Collective effects in deuteron induced reactions of aluminum

Cross sections of 27Al(d,x)22Na, 27Al(d,x)24Na, and 27Al(d,x)27Mg reactions are calculated by using TALYS 1.6 computer code with different nuclear level density models, which are composite Gilbert–Cameron model, back-shifted Fermi gas model, generalized superfluid model, and recently proposed collective semi-classical Fermi gas model in the energy range of 3–180MeV. The results are compared with the experimental data taken from EXFOR library. In these deuteron induced reactions, collective effects are investigated by means of nuclear level density models. Collective semi-classical Fermi gas model including the collective effects via the level density parameter represents the best agreement with the experimental data compared to the other level density models, especially in the low deuteron bombarding energies where the collective effects dominate.

Condensate flow in holographic models in the presence of dark matter

Holographic model of a three-dimensional current carrying superconductor or superfluid with {\it dark matter} sector described by the additional $U(1)$-gauge field coupled to the ordinary Maxwell one, has been studied in the probe limit. We investigated analytically by the Sturm-Liouville variational method, the holographic s-wave and p-wave models in the background of the AdS soliton as well as five-dimensional AdS black hole spacetimes. The two models of p-wave superfluids were considered, the so called $SU(2)$ and the Maxwell-vector. Special attention has been paid to the dependence of the critical chemical potential and critical transition temperature on the velocity of the condensate and {\it dark matter} parameters. The current $J$ in holographic three-dimensional superconductor studied here, shows the linear dependence on $T_c-T$ for both s and p-wave symmetry. This is in a significant contrast with the previously obtained results for two-dimensional superconductors, which reveal the $(T-T_c)^{3/2}$ temperature dependence. The coupling constant $\alpha$, as well as, chemical potential $\mu_D$ and the velocity $S_D$ of the {\it dark matter}, affect the critical chemical potential of the p-wave holographic $SU(2)$ system. On the other hand, $\alpha$, {\it dark matter} velocity $S_D$ and density $\rho_D$ determine the actual value of the transition temperature of the same superconductor/superfluid set up. However, the {\it dark matter} does not affect the value of the current.

Excitation function calculations for α + 93Nb nuclear reactions

In this study, the excitation functions of alpha-induced reactions on the 93Nb target nucleus were calculated by using ALICE-ASH code. The hybrid model, Weisskopf-Ewing model and geometry dependent hybrid model in this code were used to understand the alpha-niobium interaction. The contribution on the nuclear interaction of compound and pre-compound processes, with variation of the incident alpha particle energy, was presented. Furthermore, the reaction cross sections were calculated by using different level density models such as Superfluid nuclear model, Fermi gas model and Kataria-Ramamurthy Fermi gas model. Obtaining a good agreement between the calculated and the measured cross sections, the exciton numbers and the nuclear level density models were varied. Finally, the proper choice of the exciton numbers and the nuclear level density models was found to be quite important in order to obtain the more realistic cross section values.

Zero temperature holographic superfluids with two competing orders

We initiate the investigation of the zero temperature holographic superfluids with two competing orders, where besides the vacuum phase, two one band superfluid phases, the coexistent superfluid phase has also been found in the AdS soliton background for the first time. We construct the complete phase diagram in the $e-\mu$ plane by numerics, which is consistent with our qualitative analysis. Furthermore, we calculate the corresponding optical conductivity and sound speed by the linear response theory. The onset of pole of optical conductivity at $\omega=0$ indicates that the spontaneous breaking phase always represents the superfluid phase, and the residue of pole is increased with the chemical potential, which is consistent with the fact that the particle density is essentially the superfluid density for zero temperature superfluids. In addition, the resulting sound speed demonstrates the non-smoothness at the critical points as the order parameter of condensate, which indicates that the phase transitions can also be identified by the behavior of sound speed. Moreover, as expected from the boundary conformal field theory, the sound speed saturates to $\frac{1}{\sqrt{2}}$ at the large chemical potential limit for our two band holographic superfluid model.

Analytical study on holographic superfluid in AdS soliton background

We analytically study the holographic superfluid phase transition in the AdS soliton background by using the variational method for the Sturm-Liouville eigenvalue problem. By investigating the holographic s-wave and p-wave superfluid models in the probe limit, we observe that the spatial component of the gauge field will hinder the phase transition. Moreover, we note that, different from the AdS black hole spacetime, in the AdS soliton background the holographic superfluid phase transition always belongs to the second order and the critical exponent of the system takes the mean-field value in both s-wave and p-wave models. Our analytical results are found to be in good agreement with the numerical findings.

Nuclear-level densities in the 49V and 57Co nuclei on the basis of evaporated-neutron spectra in (p, n) and (d, n) reactions

The spectra of neutrons from the reactions 49Ti(p, n)49V and 57Fe (p, n)57Co were measured in the range of proton energies between 8 and 11 MeV along with their counterparts from the reactions 48Ti(d, n)49V and 56Fe (d, n)57Co at the deuteron energies of 2.7 and 3.8 MeV. These measurements were conducted with the aid of a time-of-flight fast-neutron spectrometer on the basis of the EGP-15 pulsed tandem accelerator of the Institute for Physics and Power Engineering (IPPE, Obninsk). An analysis of measured data was performed within the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations based on the Hauser–Feshbach formalism of statistical theory were carried out with nuclear-level densities given by the generalized superfluid model of the nucleus, the backshifted Fermi-gas model, and the Gilbert–Cameron composite formula. The nuclear-level densities of 49V and 57Co and their energy dependences were determined. The results were discussed together with available experimental data and data recommended by model systematics.

First-order superfluid to valence-bond solid phase transitions in easy-planeSU(N)magnets for smallN

We consider the easy-plane limit of bipartite SU($N$) Heisenberg Hamiltonians which have a fundamental representation on one sublattice and the conjugate to fundamental on the other sublattice. For $N=2$ the easy plane limit of the SU(2) Heisenberg model is the well known quantum XY model of a lattice superfluid. We introduce a logical method to generalize the quantum XY model to arbitrary $N$, which keeps the Hamiltonian sign-free. We show that these quantum Hamiltonians have a world-line representation as the statistical mechanics of certain tightly packed loop models of $N$-colors in which neighboring loops are disallowed from having the same color. In this loop representation we design an efficient Monte Carlo cluster algorithm for our model. We present extensive numerical results for these models on the two dimensional square lattice, where we find the nearest neighbor model has superfluid order for $N\leq 5$ and valence-bond order for $N> 5$. By introducing SU($N$) easy-plane symmetric four-spin couplings we are able to tune across the superfluid-VBS phase boundary for all $N\leq 5$. We present clear evidence that this quantum phase transition is first order for $N=2$ and $N=5$, suggesting that easy-plane deconfined criticality runs away generically to a first order transition for small-$N$.

Proton capture cross sections on neutron-magicSm144at astrophysically relevant energies

Background: The $p$ nuclei, which are not produced by neutron capture processes, are present with a typical isotopic abundance of 0.01%--0.3%. Abundance decreases with an increase in atomic number. However, the neutron-magic isotopes of $^{92}\text{Mo}$ and $^{144}\text{Sm}$ exhibit unusually large abundances in comparison. A combination of proton and $\ensuremath{\alpha}$-particle capture reactions and neutron emission reactions are key to understanding this issue. Currently, complex network calculations do not have access to much experimental data, and hence require theoretically predicted reaction rates in order to estimate final abundances produced in nucleosynthesis.Purpose: Few experimental cross sections of $(p$,\ensuremath{\gamma}) reactions on heavy nuclides with mass numbers of 130--150 have been reported. The $^{144}\text{Sm}(p,\phantom{\rule{0.16em}{0ex}}\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{145}\text{Eu}$ reaction is the main destruction pathway for the nucleosynthesis of the $^{144}\text{Sm}$ nuclide. In the present paper, experimental cross sections of the $^{144}\text{Sm}(p,\phantom{\rule{0.16em}{0ex}}\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{145}\text{Eu}$ reaction at a range including astrophysically relevant energies for the $p$ process were determined to compare with theoretical predictions using the Hauser-Feshback statistical model.Methods: The $^{144}\text{Sm}$ was deposited on a high-purity Al foil with the molecular plating method. Stacks consisting of Ta degrader foils, $^{144}\text{Sm}$ targets, and Cu foils used as flux monitors were irradiated with 14.0-MeV proton beams. The $^{144}\text{Sm}(p,\phantom{\rule{0.16em}{0ex}}\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{145}\text{Eu}$ cross sections were determined from the $^{145}\text{Eu}$ activities and the proton fluence estimated from the $^{65}\text{Zn}$ activity in the Cu monitor foil. The proton energies bombarded on each $^{144}\text{Sm}$ target were estimated using srim2013.Results: We determined the $^{144}\text{Sm}(p,\phantom{\rule{0.16em}{0ex}}\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{145}\text{Eu}$ cross sections at proton energies between 2.8 and 7.6 MeV. These energies encompass nucleosynthesis temperatures between 3 and 5 GK. The cross sections at energies higher than 3.8 MeV agreed well with theoretically predicted cross sections using talys using the generalized superfluid (GS) model for level densities. However, calculations using non-smoker overestimated the cross section. When the components of the energy uncertainties in the experimental cross sections were corrected, the cross sections at energies lower than 3.8 MeV showed comparable values with talys but higher than those predicted by both non-smoker and talys.Conclusions: talys using the GS model reproduced well the experimental cross sections without correction of the proton widths at energies between 2.8 and 7.6 MeV. Thus, the reaction rates of $^{144}\text{Sm}(p,\phantom{\rule{0.16em}{0ex}}\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{145}\text{Eu}$ in the stellar environment at 2.5--5 GK estimated with talys corresponded with those by the experimental cross section within 10%. However, the reaction rates depended on the extrapolation of the cross section at energies of 0--2.8 MeV at temperatures of 0.5--2.5 GK. The reaction rate estimated by talys employing the GS model showed an uncertainty within a factor of 2 at 1.5--3.5 GK for nucleosynthesis temperatures of the $p$ nuclei.