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Atmospheric traces of radioactive xenon, in particular $$^{131m}{\text {Xe}}$$ , $$^{133}{\text {Xe}}$$ , $$^{133m}{\text {Xe}}$$ and $$^{135}{\text {Xe}}$$ , can provide “smoking gun” evidence to classify underground nuclear fission reactions. Current software used to quantify isomer concentrations relies on a Region of Interest (ROI) method to sort beta-gamma coincidence counts. This experiences errors when classifying nuclides, especially with metastable nuclides, due to the difficulty of deconvoluting overlapping ROIs and accounting for shifts in detector calibration over time. To address this uncertainty, our technique mathematically models the distinctive peaks in an isomer’s beta-gamma spectrum. The function representations are then fitted to measured spectra to determine the concentrations of the primary isomers in the sample. From this proof-of-concept, we hope to create a more precise and accurate system to detect nuclear fission reactions.

Rutherford’s studies of radioactivity and the structure of atoms led after his death to the discovery of nuclear fission, and subsequently the rapid development of reactors and nuclear weapons. His...

How can it be that uranium, thorium etc. are key in star dynamism with nuclear fission, when these atoms are barely visible in spectrometry data ? The answer of wavelength deformations of the uranium, thorium… gamma rays in the plasma, making data undecipherable directly, is drawn from previous works of the author. The paper also explains why, however, 235U appears in “excess” in meteors by developing simple comments on the fission cross-sections and building as well on earlier works of the author and on super-symmetry theory. In both cases, the concept of squeezed states and the associated anti-squeezed states, in application of Heisenberg’s uncertainty relation, happen to be extremely helpful to the demonstration. This eventually helps explaining the dynamism of the collapse before explosion in standard supernovas. More elements on super-symmetry are discussed in conclusion together with a return on the Chapter 1 of From an Einstein Syndrome to the People, where the use of the fine structure constant is justified, self-repressed behaviour (with as key the fear of anal penetration, in men) is anti-squeezed.

A neutron-physical calculation is performed for neutron-producing lead, tungsten, and natural uranium targets for a subcritical assembly controlled by a proton accelerator at 0.6, 1, and 2.5 GeV. At these high proton energies, the interaction of protons with target atoms is accompanied by a splitting reaction. In terms of the neutron yield per primary proton, this reaction is more advantageous than the fission reaction. The calculation results are used to estimate the neutron-flux densities in a subcritical multiplying assembly.

Nuclear fission is one of the most complex processes in nuclear physics, involving a strong interplay between nuclear structure and dynamics, as well as various many-body correlations and fluctuation effects. Systematically theoretical and experimental research on the fission problems is of great significance to clarify the fission mechanism, reveal the complexity of low-energy nuclear dynamics, and test the nuclear model theory based on the nuclear many-body theory. However, despite the huge theoretical effort pursued by several generations of physicists, many crucial facets of this process are still not understood at a fundamental level, warranting further exploration of its dynamics. This is more so when viewed from the microscopic theoretical point of view. In the subject of study on nuclear fission, scission dynamics represents one of the most challenging problems in many-body theory as it plays a crucial role for determining the main properties of fission fragments and the emitted light particles. In the scission and post-scission processes, the fragments can experience a rapid change in shape and thus trigger the non-adiabatic effects coming from couplings between collective and intrinsic degrees of freedom. Therefore, from microscopic point of view, a reasonable description of the entire fission process could be achieved with an adiabatic model describing the slow evolution across the barrier, followed by a non-adiabatic treatment of the scission and post-scission dynamics. In this paper, with the aid of the nuclear mean-field model and Gogny effective nucleon-nucleon interaction, a three-dimensional Cartesian mesh code of time-dependent Hartree-Fock-Bogoliubov theory (Gogny-TDHFB Code for Fission) has been developed for solving the static and/or dynamic equations with isolated or periodic boundary conditions and no further symmetry assumptions. In contrast with the Skyrme HFB, the particle-hole channel and the particle-particle channel are treated on an equal footing in the HFB calculations with the Gogny interaction (Gogny HFB). The code consists of two parts: One is the constrained HFB for calculating the adiabatic fission potential energy surface in the multi-dimensional collective phase space, the other is TDHFB for studying the dynamical process of nuclear fission. In order to describe the extremely large deformation of nuclei in the direction of fission, the basis functions in the spatial grid points of the Lagrange mesh are introduced with respect to the direction of the z -axis, and the deformation harmonic oscillator eigenfunctions are used as the basis functions in the ( x , y ) directions. In the calculation of multi-dimensional potential energy surfaces, the constraints are imposed on expectation values of the multi-pole moments Q lm and the augmented Lagrangian method (ALM) is exploited for multi-constrained calculations. A parallel interface using the message passing interface (MPI) library has been implemented for large-scale calculations on massively parallel computers. Under the help of Gogny-TDHFB Code for Fission and by mainly focusing on the scission process, various aspects including the nuclear fission processes, the multi-dimensional potential energy surface, the configuration of scission point, more importantly, the non-adiabatic dynamics in the course of deformation from saddle to scission and also in post-scission are microscopically investigated in order to make clarification on the fission mechanisms, the nature of scission and some other basic problems. As an example, the spontaneous fission process of 240Pu has been studied. The results on the non-adiabatic dynamics in the course of deformation from saddle to scission and also in post-scission show that the pairing correlation plays crucial roles in the scission dynamics of nuclear fission.

Problems of describing experimental data on the angular distributions of fragments of nuclear fission induced by intermediate-energy neutrons are discussed. A way of calculating angular distributions based on using the TALYS program is proposed. The capabilities of the technique for obtaining new information on the fission process and reactions at intermediate energies are shown by the example of describing data obtained for the $${}^{{237}}{\text{Np}}$$ nucleus.

A time-of-flight spectrometer was used to compare the masses of nuclear fission fragments before and after their passage through the carbon foil, event by event. For all the registered fragments, there was a significant loss of mass of the fragment, and the registered fragment-residue turned out to be a magic nucleus. For spontaneous fission of 252Cf nuclei, the effect was observed for both light and heavy mass peaks. This gives grounds to assume that the fragment of the conventional binary fission is born in the shape isomer state, which looks like a di-nuclear system consisting of a magical core and a light cluster.

An experiment in which the fission of uranium-238 upon bombardment with neutrons is demonstrated in the context of an undergraduate lab course. The occurrence of fission is shown by means of gamma spectroscopy which reveals the presence of the fission product strontium-92. In addition, we also investigate the reaction in which plutonium-239 is formed after neutron activation of the uranium, with neptunium-239 as an intermediary step. From the gamma spectra, it is found that both reactions are demonstrated with a significance of more than 5 σ. For the fission reaction, a cross section of ( 2.8 ± 1.4 ) × 10 − 2 barn is inferred.An experiment in which the fission of uranium-238 upon bombardment with neutrons is demonstrated in the context of an undergraduate lab course. The occurrence of fission is shown by means of gamma spectroscopy which reveals the presence of the fission product strontium-92. In addition, we also investigate the reaction in which plutonium-239 is formed after neutron activation of the uranium, with neptunium-239 as an intermediary step. From the gamma spectra, it is found that both reactions are demonstrated with a significance of more than 5 σ. For the fission reaction, a cross section of ( 2.8 ± 1.4 ) × 10 − 2 barn is inferred.

We have developed a position-sensitive Parallel Plate Avalanche Counter (PPAC) to detect the fission fragments and reconstruct the fission reaction plane in the experiment of studying nuclear equation of state (nEOS) by means of heavy ion collision (HIC). This experiment put forward high requirements for the performances of PPAC, such as the time resolution, efficiency and position resolution. According to these requirements we designed the PPAC with an active area of 240 mm × 280 mm working at low gas pressure. The results show that time resolution could be less than 300 ps. Position resolution is consistent with the theoretical calculation about 1.35 mm. Detection efficiency could be approaching 100% gradually with the voltage increasing in different gas pressures. The performances of PPAC have also been verified in beam experiment. Each set of anode wires can be accurately separated in the position spectrum. In the beam experiment, we also got the back-to-back correlation of fission fragments which is one of the direct signals characterizing binary decay. Keywords: PPAC, nEOS, Time resolution, Position resolution, Efficiency

The expression of dependence of the average total kinetic energy of fission fragments on the excitation energy of the fissioning system is obtained in a simple model, which takes into account the statistical and quantum properties. The experimental data of the average total kinetic energy of fragments formed in the fission of nuclei $^{234,236,239}$U and $^{240}$Pu are well described using the obtained expression in the wide range of the excitation energy of these nuclei. The origin of the energy dependence of the average total kinetic energy is discussed in details.

Background: $\ensuremath{\beta}$-delayed neutron emission and fission are essential in $r$-process nucleosynthesis. Although the number of experimental studies covering $r$-process nuclei has recently increased, the uncertainties of $\ensuremath{\beta}$-delayed neutron emission and fission are still large for $r$-process simulations.Purpose: Our aim is to introduce a theoretical framework for the description of $\ensuremath{\beta}$-delayed neutron-emission and fission rates based on relativistic nuclear energy density-functional and statistical models and investigate their properties throughout the nuclide map.Methods: To obtain $\ensuremath{\beta}$ strength functions, the relativistic proton-neutron quasiparticle random-phase approximation is employed. Particle evaporations and fission from highly excited nuclear states are estimated by the Hauser-Feshbach statistical model. $\ensuremath{\beta}$-delayed neutron branching ratios ${P}_{n}$ are calculated and compared with experimental data, and the $\ensuremath{\beta}$-delayed fission branching ratio ${P}_{f}$ are also assessed by using different fission barrier data.Results: Calculated ${P}_{n}$ are in a good agreement with the experimental data and the root mean square deviation is comparable to results of preceding works. It is found that energy withdrawal by $\ensuremath{\beta}$-delayed neutron-emission sensitivity varies ${P}_{n}$, especially for nuclei near the neutron drip line. ${P}_{f}$ depend sensitively on fission barrier data. It is found that not only the barrier height but also the number of barrier humps is important to evaluate ${P}_{f}$.Conclusions: The framework introduced in this work provides an improved theoretical description of the $\ensuremath{\beta}$-delayed neutron emission and fission. Since ${P}_{f}$ as well as ${P}_{n}$ depend strongly on fission barrier information, four kinds of fission barrier data are used in this work to allow further sensitivity studies of the $r$-process nucleosynthesis on the nuclear fission. More studies on fission barrier are highly requested to assess the role of $\ensuremath{\beta}$-delayed fission in the $r$-process study. A complete set of calculated data for $\ensuremath{\beta}$-delayed neutron emission and fission are summarized as a table in supplemental material for its use in $r$-process studies as well as to complement a part of nuclear data in which no experimental data are available.

We discuss a possibility that the so-called reactor antineutrino anomaly (RAA), which is a deficit of the ν¯e rates in the reactor experiments in comparison to the theoretical expectations, can at least in part be explained by applying a quantum field-theoretical approach to neutrino oscillations, which in particular predicts a small deviation from the classical inverse-square law at short (but still macroscopic) distances between the neutrino source and detector. An extensive statistical analysis of the current reactor data on the integrated ν¯e event rates vs. baseline is performed to examine this speculation. The obtained results are applied to study another long-standing puzzle—gallium neutrino anomaly (GNA), which is a missing νe flux from 37Ar and 51Cr electron-capture decays as measured by the gallium–germanium solar neutrino detectors GALLEX and SAGE.

Background: So far the feasibility of nuclear reactions has been studied only through the evaluation of the reaction rate, which gives us information about the kinetics, while the thermodynamic analysis has been limited to evaluations of the change in enthalpy without any consideration of the change in entropy. Methods: This work examines the thermodynamics of nuclear fusion reactions through a simplified approach. The analysis introduces the thermodynamic study of fission and fusion reactions through their comparison with a chemical process. Results: The main result is that fission reactions are always spontaneous (ΔG < 0) since a lot of energy is released in the form of heat and the system moves spontaneously towards a more disordered state. In contrast, fusion reactions are spontaneous only when the enthalpic contribution of the change in Gibbs free energy overcomes the entropic contribution. This condition is verified when the temperature of the process is below a characteristic value T*, calculated as the ratio between the energy corresponding to the mass defect and the change of entropy of the fusion reaction. Conclusions: Due to the unavailability of data related to entropy changes in fusion reactions, only a qualitative thermodynamic analysis has been carried out. Through such analysis, the influence of the operating conditions over the spontaneity of fusion processes has been discussed. The final considerations emphasize the role of the thermodynamics analysis that should be implemented in the current studies that, so far, have been mainly based on the assessment of the reaction rate and exothermicity of fusion reactions.

This work is a next step toward the study of physical properties of the Accelerator Driven System (ADS) in which a deeply subcritical active core (512 kg natural uranium target) is irradiated by a pulsed beam of relativistic particles. The measurement of the total number of fission reactions is a fundamental task in the given research. The estimated method of determining the number of fission reactions based on activation detectors is analyzed. Our interest has been focused on the study of the proton- and neutron-induced fission reaction inside the high-energy particle beam volume. The fission products of fission reactions have been measured employing natural uranium activation detectors and germanium gamma detectors (HPGe). Experimental data are taken from the QUINTA experiment performed at JINR, Dubna, in November 2014. The presented method gives an effective possibility of estimating the measured number of fission reactions induced by neutrons and high-energy protons simultaneously.

The fission of the 181Re∗ nucleus formed via the 12C +169Tm reaction is studied at ELab= 77–89 MeV within the dynamical cluster model (DCM) for the choices of spherical as well as deformed fragments originated in binary decay channels of the of collective clusterization approach. The mass distribution of the compound nucleus 181Re∗ is analyzed for both choices and compared with the available data, and consequently the probable fission fragments are identified. The barrier height, barrier modification, and barrier penetrability of the fission fragments are investigated. The total fission cross-sections are calculated for spherical as well as deformed choices of fragmentation, and they are in nice agreement with experimental data. In addition, the fission emission times and the decay widths of the fission fragments are predicted for comparison with future experiments. Finally, the preformation behavior of spontaneous and induced fission paths are compared to give a better insight of the decay mechanism of 181Re nucleus.

A comparison is made of two theoretical approaches to describing the coefficients of T-odd asymmetries in the angular distributions of prompt γ-quanta and neutrons evaporated from thermalized fragments of the binary fission of non-oriented target nuclei by cold polarized neutrons, and in angular distributions of pre-scission α particles emitted in the same ternary nuclear fission: the classical approach, which is based on trajectory calculations, and the quantum approach, which is based on quantum fission theory. It is shown that the coefficients for all of the considered nuclei are of a quantum nature and vanish in the classical approach when there is no interference from the fission amplitudes of the different neutron resonances of a compound nucleus. The advantages of the quantum approach versus the classical one are demonstrated.

In criticality and stability studies of the nuclear reactor, it is important to evaluate the impact of the uncertainties of the basic nuclear data (cross sections) on the different neutron parameters. In this work sensitivity and uncertainly analysis of KRITZ-2:19 experiment at 21.1 °C was carried out with respect to cross-section uncertainties of 1H, 10B, 16O, 235U, 238U, 239Pu, 240Pu, 241Pu and 241Am isotopes on the effective multiplication factor ” keff ” for JENDL-4.0 and ENDF/B-VII.1 evaluated libraries. Sensitivity vectors calculated by card KSEN/MCNP6.1 have been combined with the covariance matrices (from ENDF/B-VII.1, JENDL-4.0, and/or ENDL-3.2) generated by the ERRORJ module of NJOY2016 to produce nuclear data uncertainties. Comparison between JENDL-4.0 and ENDF/B-VII.1 evaluated libraries consistency among the calculated-to-experiment values of keff and the overall computational uncertainties is discussed. The keff was found to have the largest sensitivity to fission and capture cross-sections of 239Pu for the two libraries JENDL-4.0 and ENDF/B-VII.1. Neutron fission reaction of 239Pu for the two evaluated libraries was found to contribute to the major part of the keff uncertainty due to the cross-sections. The discrepancy of the calculated and measured keff values was strongly correlated with the uncertainty in the calculated keff due to the 239Pu neutron fission cross-section uncertainty.

The proposed Compact Intense Fast NEutron Facility (CIFNEF) will have a wide range of applications, including the investigation of the exotic structure of neutron-rich nuclei, data for the nuclear fission , and the simulation of the neutron field in a star. To satisfy aims of producing high-intensity fast neutrons and forward neutrons with very low environmental background, the CIFNEF linac should have the capacity of accelerating continuous wave (CW) deuteron (D + ), hydrogen ( H 2 + ) and lithium (7Li 3 + ) beams to 2.5 MeV/u with maximum beam currents of 10 mA, 5 mA and 10 uA, respectively. Based on the above requirements, we proposed a novel compact linac using a combination of RFQ and DTL structures. The dynamics of RFQ and DTL are completed to meet all requirements and start-to-end simulation results show that the three ion species can be accelerated to the final energy with transmission efficiency above 99% as well as good beam quality with lower emittance growth. In addition, we performed error sensitivity analysis and combined error study to evaluate the error tolerance limits of the obtained design.

In employing the concept of the isotropy of space, the coefficients D of P-even, T-odd asymmetry in the angular distributions of prescission alpha particles emitted as third particles in the ternary fission of nonoriented target nuclei that is induced by polarized cold neutrons are expressed in the lowest orders of perturbation theory in the neutron polarization vector in terms of two P-even scalar coefficients D3 and D5 associated with, respectively, triple and quintuple correlations depending on the unit vectors kα, kLF, and σn, which determine the features of the coefficients being studied. On the basis of the above representation, the experimental values of the coefficients D3 and D5 are determined by using the experimental values of D and the angular distributions of alpha particles emitted in the analogous reaction induced by unpolarized neutrons. The resulting coefficients D3 and D5 are compared with the analogous coefficients found by means of the classical method of trajectory calculations and by means of quantum-mechanical fission theory relying on the concept that it is the rotational mechanism that is responsible for the appearance of the asymmetries being studied. It turns out that the classical method, which disregards the interference between fission amplitudes for different S-wave neutron resonances, leads to an irremovable contradiction between the calculated coefficient D3 and the analogous experimental coefficient for the 233U target nucleus. In the case of employing the quantum-mechanical approach, it is concluded that three-body calculations of the Coriolis interaction—perturbed amplitude of the angular distributions of alpha particles moving in the Coulomb fields of fission fragments are required for the 233U target nucleus.

In this paper we report on an effort to determine an optimal parameter set for the complete event fission model F R E Y A to reproduce spontaneous fission of 252 Cf(sf), 244 Cm(sf), 238 Pu(sf), 240 Pu(sf), 242 Pu(sf), and 238U(sf). Earlier studies have partially optimized the event-by-event fission model F R E Y A with respect to the available experimental data using brute force computational techniques. We have confirmed and expanded these results using a least-squares minimization based on the simulated annealing approach. We have also developed a more complete statistical picture of this optimization, consisting of a full correlation matrix for the parameters utilized by F R E Y A . The newly improved parameter values themselves, along with this correlation matrix, have led to a more well-developed physical picture of the fission process.

Hydrogen is the number 1 element in the Mendeleev table, which is practically the smallest known element. From an energy point of view, hydrogen is of particular importance, being the key element for obtaining renewable and sustainable energy, either in the form of nuclear fusion energy or as a supportive element of nuclear fission energy by enriching its fuel or by burning it in thermal burners, or thermal or external combustion engines. Hydrogen, together with oxygen and with nitrogen and phosphorus are the four vital elements, which together make up the ATP energy molecule that donates the energy of living matter at the cellular scale. That is why we considered it necessary to study several structural aspects of nuclear hydrogen in the presented paper. The dimensions and shape of the existing hydrogen nuclei will be analyzed for the purpose of their description as accurately as possible, given that the dimensions of a particular type of hydrogen nucleus are not constant, varying dynamically depending on the linear displacement speed of the nucleus. The paper examines only the three isotopic forms of nuclear hydrogen, known as relatively stable, the first completely stable and the next two relatively stable. From the fourth isotopic form up, the stability is almost inexistent, the life of such an isotope being ephemeral, which is why we did not consider it necessary to study these ephemeral forms of existence of hydrogen isotopes equal to or greater than four. The immediate applications of the theory presented are the obtaining of fusion energy, industrial.

This paper describes several approaches to propagating nuclear data uncertainty in integral capture and fission reaction rates, focusing on the spectral hardness indices of 193Ir(n,n′)193mIr/191Ir(n,g)192Ir and 238U(n,f)/235U(n,f) in fast critical assemblies. Uncertainties in the nuclear data were propagated through the following methods: a sensitivity method (utilizing first order perturbation and covariance matrices), a BFMC method (random cross sections generated through covariance matrices), and Total Monte Carlo method (random cross sections generated from varying nuclear parameters). The uncertainty estimates from the three approaches are evaluated against the associated experimental uncertainties of a ZEUS/COMET critical assembly irradiation. The uncertainty estimates of the three approaches agree fairly well, and contribute a significant portion to the overall uncertainty of the spectral hardness indices.

A detailed investigation on the relative isotopic distributions has been carried out for the first time in case of even-even correlated fission fragments for the $^{235}\mathrm{U}({n}_{\text{th}},f$) fission reaction. High-statistics data were obtained in a prompt $\ensuremath{\gamma}$-ray spectroscopy measurement during the EXILL campaign at ILL, Grenoble, France. The extensive off-line analysis of the coincidence data have been carried out using four different coincidence methods. Combining the results from two-dimensional $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ and three-dimensional $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence analysis, a comprehensive picture of the relative isotopic yield distributions of the even-even neutron-rich fission fragments has emerged. The experimentally observed results have been substantiated by the theoretical calculations based on a novel approach of isospin conservation, and a reasonable agreement has been obtained. The calculations following the semiempirical GEF model have also been carried out. The results from the GEF model calculations are found to be in fair agreement with the experimental results.

A recent analysis of experimental data [J. Wilson $et. al$, Nature $\mathbf 590$, 566 (2021)] found that the angular momenta of nuclear fission fragments are uncorrelated. Based on this finding, the authors concluded that the spins are therefore determined only $after$ scission has occurred. We show here that the nucleon-exchange mechanism, as implemented in the well-established event-by-event fission model $\mathtt{FREYA}$, while agitating collective rotational modes in which the two spins are highly correlated, nevertheless leads to fragment spins that are largely uncorrelated. This fact invalidates the reasoning of those authors. Furthermore, it was reported [J. Wilson $et. al$, Nature $\mathbf 590$, 566 (2021)] that the mass dependence of the average fragment spin has a sawtooth structure. We demonstrate that such a behavior naturally emerges when shell and deformation effects are included in the moments of inertia of the fragments at scission., 5 pages, 2 figures

When a heavy atomic nucleus splits (fission), the resulting fragments are observed to emerge spinning1; this phenomenon has been a mystery in nuclear physics for over 40 years2,3. The internal generation of typically six or seven units of angular momentum in each fragment is particularly puzzling for systems that start with zero, or almost zero, spin. There are currently no experimental observations that enable decisive discrimination between the many competing theories for the mechanism that generates the angular momentum4–12. Nevertheless, the consensus is that excitation of collective vibrational modes generates the intrinsic spin before the nucleus splits (pre-scission). Here we show that there is no significant correlation between the spins of the fragment partners, which leads us to conclude that angular momentum in fission is actually generated after the nucleus splits (post-scission). We present comprehensive data showing that the average spin is strongly mass-dependent, varying in saw-tooth distributions. We observe no notable dependence of fragment spin on the mass or charge of the partner nucleus, confirming the uncorrelated post-scission nature of the spin mechanism. To explain these observations, we propose that the collective motion of nucleons in the ruptured neck of the fissioning system generates two independent torques, analogous to the snapping of an elastic band. A parameterization based on occupation of angular momentum states according to statistical theory describes the full range of experimental data well. This insight into the role of spin in nuclear fission is not only important for the fundamental understanding and theoretical description of fission, but also has consequences for the γ-ray heating problem in nuclear reactors13,14, for the study of the structure of neutron-rich isotopes15,16, and for the synthesis and stability of super-heavy elements17,18. γ-ray spectroscopy experiments on the origin of spin in the products of nuclear fission of spin-zero nuclei suggest that the fission fragments acquire their spin after scission, rather than before.

Nuclear fission is hindered by dissipation. Using the stochastic Langevin model, we calculate the drop of fission cross sections caused by friction with respect to its standard statistical-model values, ${\ensuremath{\sigma}}_{f}^{\mathrm{drop}}$, as a function of the presadde dissipation strength $(\ensuremath{\beta})$ for $^{226}\mathrm{U}$, $^{234}\mathrm{U}$, and $^{242}\mathrm{U}$. It is shown that the sensitivity of ${\ensuremath{\sigma}}_{f}^{\mathrm{drop}}$ to $\ensuremath{\beta}$ is substantially enhanced with increasing the isospin of the U fissioning system. Furthermore, we find that under typical conditions of excitation energy and angular momentum populating $^{240}\mathrm{U}$ (via radioactive beams) and $^{200}\mathrm{Tl}$ (via stable beams), the fission cross section of the high-isospin heavy $^{240}\mathrm{U}$ demonstrates a greater sensitivity to friction than that of the light $^{200}\mathrm{Tl}$. Our findings suggest that on the experimental side, to accurately probe presaddle dissipation with fission cross sections of heavy nuclei, it is useful to choose radioactive nuclear beams induced reactions as a way to populate excited heavy fissioning systems with high isospin.

During nuclear fission, a heavy nucleus splits into two rotating fragments. The associated angular momentum is large, yet the mechanism of its generation and its dependence on the mass of fragments remain poorly understood. In this Letter, we provide the first microscopic calculations of angular momentum distributions in fission fragments for a wide range of fragment masses. For the benchmark case of $^{239}$Pu($n_{\text{th}}$,f), we find that the angular momentum of the fragments is largely determined by the nuclear shell structure and deformation, and that the heavy fragments therefore typically carry less angular momentum than their light partners. We use the fission model $\tt{FREYA}$ to simulate the emission of neutrons and photons from the fragments. The dependence of the angular momenta on fragment mass after the emission of neutrons and statistical photons is linear for the heavy fragments and either constant or weakly linear for the light fragments, consistent with the universal sawtooth pattern suggested by recent experimental data. Finally, we observe that using microscopic angular momentum distributions modifies the number of emitted photons significantly., 7 pages, 2 figures

Fission properties of the actinide nuclei are deduced from theoretical analysis. We investigate potential energy surfaces and fission barriers and predict the fission fragment mass-yields of actinide isotopes. The results are compared with experimental data where available. The calculations were performed in the macroscopic-microscopic approximation with the Lublin-Strasbourg Drop (LSD) for the macroscopic part and the microscopic energy corrections were evaluated in the Yukawa-folded potential. The Fourier nuclear shape parametrization is used to describe the nuclear shape, including the non-axial degree of freedom. The fission fragment mass-yields of considered nuclei are evaluated within a 3D collective model using the Born-Oppenheimer approximation., Comment: 11 pages, 12 figures, submitted to the Chinese Physics C. arXiv admin note: text overlap with arXiv:2001.08652

Potential energy surfaces and fission barriers of superheavy nuclei are analyzed in the macroscopic-microscopic model. The Lublin-Strasbourg Drop (LSD) is used to obtain the macroscopic part of the energy, whereas the shell and pairing energy corrections are evaluated using the Yukawa-folded potential. A standard flooding technique has been used to determine the barrier heights. It was shown the Fourier shape parametrization containing only three deformation parameters reproduces well the nuclear shapes of nuclei on their way to fission. In addition, the non-axial degree of freedom is taken into account to describe better the form of nuclei around the ground state and in the saddles region. Apart from the symmetric fission valley, a new very asymmetric fission mode is predicted in most superheavy nuclei. The fission fragment mass distributions of considered nuclei are obtained by solving the 3D Langevin equations., Comment: 20 pages, 17 figures