Narrow Results

The results of the investigation of the binary break-up of some fraction of the fission fragments from the binary fission of ${}^{252}$Cf(sf), while they pass through the Ta foil are presented. The “double-hit” experimental approach, which implies that both partners of the break-up are detected in the same PIN diode, was applied. In this work, special attention is paid to the break-up, accompanied by the light charged particles, that was revealed in three experiments performed under three different settings. Consistency of the results from all three experiments gives evidence of the reliability of the experimental findings.

Nuclear fission has been modeled notoriously using two approaches method, macroscopic and microscopic. This work will propose another approach, where the nucleus is treated as a toy model. The aim is to see the usefulness of particle distribution in fission yield calculation. Inasmuch nucleus is a toy, then the Fission Toy Model (FTM) does not represent real process in nature completely. The fission event in FTM is represented by one random number. The number is assumed as width of distribution probability of nucleon position in compound nuclei when fission process is started. By adopting the nucleon density approximation, the Gaussian distribution is chosen as particle distribution. This distribution function generates random number that randomizes distance between particles and a central point. The scission process is started by smashing compound nucleus central point into two parts that are left central and right central points. The yield is determined from portion of nuclei distribution which is proportional with portion of mass numbers. By using modified FTM, characteristic of particle distribution in each fission event could be formed before fission process. These characteristics could be used to make prediction about real nucleons interaction in fission process. The results of FTM calculation give information that the $\gamma$ value seems as energy.

Micromegas-based detectors are used in a wide variety of neutron experiments. Their fast response meets the needs of time-of-flight facilities in terms of time resolution. The possibility of constructing low mass Micromegas detectors makes them appropriate for beam imaging and monitoring without affecting the beam quality or inducing background in parallel measurements. The good particle discrimination capability allows using Micromegas for neutron induced fission and (n, α) cross-section measurements. Their high radiation resistance make them suitable for working as flux monitors in the core of fission nuclear reactors as well as in the proximity of fusion chambers. New studies underlined the possibility of performing neutron computed tomography (CT) with Micromegas as neutron detectors, but also of exploiting its performances in experiments of fundamental nuclear physics.

In this work, the proton induced fission reaction cross-sections and fission yields are calculated for some actinides $({}^{232}\mathrm{\text{Th}}$, ${}^{233,235,236,238}\mathrm{\text{U}}$, ${}^{237}\mathrm{\text{Np}}$, and ${}^{239}\mathrm{\text{Pu}})$ using the fission barrier models of the TALYS 1.95 code. Cross-sections and fission yield calculations are carried out up to 100 MeV incident proton energies. The calculation results are compared with the available experimental data in the EXFOR library. In addition, a relative variance analysis of fission barrier models was done to determine the fission barrier model whose results best matched with the experimental results. Among the fission barrier models, the best agreement with the experimental data is obtained from the rotating-finite-range fission barrier model calculation for the $(p,f)$ reaction of the studied nuclei having the atomic mass number larger than 230. On the other hand, fission barrier heights for the studied reactions are determined using the same models.

Using an extended mapping approach and a special Painlevé–Bäcklund transformation, respectively, we obtain two families of exact solutions to the (2+1)-dimensional Boiti–Leon–Martina–Pempinelli (BLMP) system. In terms of the derived exact solution, we reveal some novel evolutional behaviors of localized excitations, i.e., fission, fusion, and annihilation phenomena in the (2+1)-dimensional BLMP system.

In this paper, the two- and three-soliton propagation of Sharma–Tasso–Olver (STO) equation for inhomogeneous media (with a variable-coefficient) are obtained. It is shown, due to the inelastic collisions, they undergo space-fission (or fusions). These soliton waves show a fusion that their nonlinear interactions are not completely elastic (or inelastic). To study some of the propagation features of pulses and their collision dynamics, the numerical simulations of the solutions are used. It is found that fusion along quasi-periodic waves is exhibited. The graded or step index waveguide under nonlinear refractive components are shown to reduce to improve soliton intensity. Further, the properties for these solutions are shown with figures. It may be found that research on new structure of soliton control has been obtained to understand real physical problems. These results have been usefully applied for long-wave and high-power transmission in telecommunication system. Moreover, stability analysis for the governing equation is investigated via the aspect of linear stability.

Advances achieved during recent years in model and ab initio descriptions of fission of metal clusters are reviewed. We focus on developments in ab initio treatment of the electronic subsystem within the jellium background model, as well as on applications of potential energy surface analysis to determining the characteristics of the fission process. We reiterate the main results obtained with the implementation of the Hartree–Fock and local density schemes for the two-center deformed jellium model. We overview the influences of the geometrical and statistical factors on the parameters of the fission process revealed recently. Also, we overview concisely the classical liquid drop model, the shell correction method, the asymmetric two-center-oscillator shell model, and the main approaches to the molecular dynamics simulations of the fission process.

A stochastic approach for fission dynamics based on one-dimensional Langevin equations was applied to investigate the effect of the nuclear dissipation on the prescission neutron multiplicity, fission probability and the fission time for the compound nucleus ²¹⁰Po in an intermediate range of excitation energies 30–120 MeV. A modified wall and window dissipation with a reduction coefficient, k_s, has been used in the Langevin equations. It was shown that the results of the calculations are in good agreement with the experimental data by using values of k_s in the range 0.28 ≤ k_s ≤ 0.50.

A two-dimensional (2D) dynamical model based on Langevin equations was applied to study the fission dynamics of the compound nuclei ²²⁸U produced in ¹⁹F + ²⁰⁹Bi reactions at intermediate excitation energies. The distance between the centers of masses of the future fission fragments was used as the first dimension and the projection of the total spin of the compound nucleus onto the symmetry axis, K, was considered as the second dimension in Langevin dynamical calculations. The magnitude of post-saddle friction strength was inferred by fitting measured data on the average pre-scission neutron multiplicity for ²²⁸U. It was shown that the results of calculations are in good agreement with the experimental data by using values of the post-saddle friction equal to 6–8 × 10²¹s^-1.

We have studied the $\alpha$-decay properties of superheavy nuclei (SHN) $Z=124$ in the range $282\le A\le 333$ using the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The calculated $\alpha$ half-lives agree with the values computed using the Viola–Seaborg systematic, the universal curve of Poenaru et al. [Phys. Rev. C83 (2011) 014601; 85 (2012) 034615] and the analytical formulas of Royer [J. Phys. G$,$ Nucl. Part. Phys.26 (2000) 1149]. To identify the mode of decay of these isotopes, the spontaneous-fission half-lives were also evaluated using the semiempirical relation given by Xu et al. [Phys. Rev. C78 (2008) 044329]. The calculated half-lives help to predict the possible isotopes of this superheavy element $Z=124$. As we could observe $\alpha$ chain consistently from the nuclei ${}^{288-312}$124, we have predicted that these nuclei could not be synthesized and detected experimentally via $\alpha$ decay as their decay half-lives are too small. The nuclei ${}^{313-318}$124 were found to have long half-lives and hence could be sufficient to detect them if synthesized in a laboratory.

Gerry Brown initiated some early studies on the coexistence of different nuclear shapes. The subject has continued to be of interest and is crucial for understanding nuclear fission. We now have a very good picture of the potential energy surface with respect to shape degrees of freedom in heavy nuclei, but the dynamics remain problematic. In contrast, the early studies on light nuclei were quite successful in describing the mixing between shapes. Perhaps a new approach in the spirit of the old calculations could better elucidate the character of the fission dynamics and explain phenomena that current theory does not model well.

Simple expression for the temperature dependence of the width of fission-fragment mass yields is obtained for high excitation energies. The width depends on the number of nucleons in nuclei, the volume and surface terms of the energy level density parameter, the temperature and the stiffness parameter of the potential related to mass-asymmetric degree of freedom. The contribution of the surface term of the energy level density parameter into the width is important at temperatures $\gtrsim 1$MeV.

In this paper, we applied the method developed by Santhosh and Safoora in [Phys. Rev. C  94 (2016) 024623; 95 (2017) 064611] to theoretically investigate the fusion, evaporation-residue (ER) and fission cross-sections of the synthesis of the unknown superheavy ${}^{309,312}$126 nuclei produced by using the ${}^{58}$Ni + ${}^{251}$Cf and ${}^{64}$Zn + ${}^{248}$Cm combinations. The charge asymmetry, mass asymmetry and fissility of the DiNuclear System (DNS) in the synthesis of the mentioned combinations are also estimated. The calculated results show that the ER cross-sections for the synthesis of the ${}^{309-317}$126 nuclei are predicted to be much less than 1.0fb. In particular, it has been found that there may exist a valley of the ER cross-sections in the synthesis of a superheavy $Z=126$ element, which produces the ${}^{313}$126 isotope. Subsequently, a model for the mass dependence of the ER cross-section in the synthesis of the ${}^{307-320}$126 isotopes has been proposed for the first time. On the other hand, the quasi-fission process strongly dominates over the fusion in the two concerned interacting systems. The present results, together with those reported in the previous studies, indicate that the investigated projectile–target combinations are not capable for the synthesis of the ${}^{309,312}$126 isotopes due to tiny fusion cross-sections (about 2–3zb), which go beyond the limitations of available facilities. Further studies are thus recommended to search for alternative interacting systems. In conclusion, this work provides useful information for the synthesis of the gap isotopes ${}^{308-317}$126, which have not been well studied up to date.

The fusion evaporation residue (ER) cross-sections ${\sigma }_{xn}$ for the decay of compound nucleus (CN) ${}^{252,254,255,256}$No${}^{\ast }$ via 1$n$–4$n$ decay channels, synthesized in ${}^{204,206,207,208}$Pb$+$${}^{48}$Ca reaction, are studied, including deformations ${\beta }_{2i}$ for cold-optimum orientations ${𝜃}_i$ at various ${}^{48}$Ca excitation energies of $E^{\ast }=20$ to 45MeV. For the nuclear interaction potentials, we use the Skyrme energy density functional (SEDF)-based on semi-classical extended Thomas Fermi (ETF) approach under frozen density approximation on our earlier study of fusion ER cross-section for the decay of ${}^{252,254-256}$No${}^{\ast }$, via 1$n$–4$n$ decay channels synthesized in ${}^{204,206-208}$Pb$+$${}^{48}$Ca reaction based on the Dynamical cluster-decay model (DCM) using the pocket formula for nuclear proximity potential in which the above reaction was investigated by using hot-optimum orientations. In this work the above reaction has been investigated in two parts, in the first part, $E^{\ast }<25$MeV is used for cold elongated configurations and in the second part, $E^{\ast }>25$MeV is used for hot compact configurations. The Skyrme forces used here are the old SIII, and new GSkI and KDE0(v1) given for both normal and isospin-rich nuclei, with densities added in frozen density approximation. Interestingly, independent of the Skyrme force used, the DCM gives an excellent fit within one-parameter fitting of $\mathrm{\Delta }R$ to the measured data on fusion ER for cold fusion. Of all the three Pb-isotopes and three $E^{\ast }$ considered, at each $E^{\ast }$, the $\mathrm{\Delta }R$ is largest for compound system with mass numbers 256 and 254, and smallest for 252, which means that the neutrons emission occur earliest for 256, then 255 followed by 254 and finally for 252, in complete agreement with experimental data. The possible fusion–fission (ff) and quasi-fission (qf) mass-regions of fragments on DCM are also predicted. The DCM with Skyrme forces is further used to look for all the possible target-projectile ($t$-$p$) combinations forming the “cold” CN ${}^{254}$No${}^{\ast }$ at the CN excitation energy of $E^{\ast }$ for “optimum cold” configurations. The fusion ER cross-sections, for the proposed new reactions in synthesizing the CN ${}^{254}$No${}^{\ast }$, are also estimated for the future experiments.

A stochastic approach based on four-dimensional (4D) dynamical model has been used to simulate the fission process of the excited compound nuclei ${}^{213}$Fr, ${}^{215}$Fr and ${}^{217}$Fr produced in fusion reactions. Effects of isospin and dissipation coefficient of the $K$ coordinate, ${\gamma }_k$, on estimation of the evaporation residue (ER) cross-section, the prescission neutron multiplicity, the variance of the mass and energy distributions of fission fragments and the anisotropy of fission fragments angular distribution have been investigated for the excited compound nuclei ${}^{213}$Fr, ${}^{215}$Fr and ${}^{217}$Fr. Three collective shape coordinates $(c,h,\alpha )$ plus the projection of total spin of the compound nucleus to the symmetry axis, $K$, were considered in the 4D dynamical model. In the 4D dynamical model, the magnitude of the dissipation coefficient of $K$, ${\gamma }_k$, was considered as a free parameter and its magnitude inferred by fitting measured data on the ER cross-section. Results of the extracted dissipation coefficients of $K$ for different isotopes of Fr were shown that the magnitude of the dissipation coefficient of $K$ increases with decreasing isospin of fissioning compound nucleus. It was also shown that the prescission neutron multiplicity and the anisotropy of fission fragments angular distribution increase with increasing isospin whereas the variance of the mass and energy distributions of fission fragments decrease with increasing isospin of fissioning compound nucleus. Furthermore, it was shown that the calculated values of prescission neutron multiplicity and the variance of the mass distribution of fission fragments for the excited compound nuclei ${}^{213}$Fr, ${}^{215}$Fr and ${}^{217}$Fr decrease with the dissipation strength of $K$, whereas the variance of the energy distribution of fission fragments and the anisotropy of fission fragments angular distribution increase with the dissipation strength of $K$.

In this paper, a stochastic approach based on two-dimensional dynamical model was used to simulate the fission process of the excited compound nucleus ${}^{178}$W produced in ${}^{19}\mathrm{\text{F}}{+}^{159}\mathrm{\text{Tb}}$ reaction. In the dynamical calculations, the elongation parameter of the nucleus was used as the first dimension and the projection of the total spin of the compound nucleus onto the symmetry axis, $K$, considered as the second dimension. The average pre-fission multiplicities of neutron, light charged particles and the total kinetic energy of the fission fragments were calculated for ${}^{178}$W and the results of calculations compared with the experimental data over a wide range of excitation energy. In the dynamical calculations, dissipation was generated through the chaos weighted wall and window friction formula and the dissipation coefficient of $K,{\gamma }_k$, was considered as a free parameter and its magnitude inferred by fitting measured data on the average pre-fission multiplicities of neutron and proton for the compound nucleus ${}^{178}$W. It was shown that the results of calculations are in good agreement with the experimental data by using the dissipation coefficient of $K$ in the range ${\gamma }_k=(0.180-0.210){(\mathrm{\text{MeV zs}})}^{-1/2}$. It was also shown that the results of calculations with ${\gamma }_k=(0.180-0.210){(\text{MeV zs})}^{-1/2}$ provide a better agreement with the experimental data than with a deformation-dependent dissipation coefficient. Furthermore, it was also shown that differences between the results of calculations for the total kinetic energy of the fission fragments calculated by using different values of dissipation coefficient of $K$ are small.

In this paper, the fission of the single stars and galaxies in the mass-asymmetry (mass transfer) coordinate is considered. Using the potential energy derived as a function of mass asymmetry, the possibility of the formation of binary stars (binary galaxies) from the single stars (single galaxies) is studied.

In this paper, we model the fission process by assuming that at certain elongation, after crossing the fission barrier, a fissile nucleus can be treated as a superposition of dinuclear systems (DNS). The distribution of primary fission fragments is described as a result of competition between evolution of initially formed DNS and its decay in relative distance. The level densities required for the calculations were microscopically derived accounting for deformation and excitation energy effects. The calculations performed for even ${}^{244-260}$Fm isotopes give overall good description of mass and neutron multiplicity distributions. To describe sudden onset of symmetric fission in ${}^{258}$Fm, the fissile nucleus is treated as superposition of DNS at smaller elongations than for lighter Fm isotopes, which is in line with significant reduction of half-life for ${}^{258}$Fm. Our results indicate the presence of bimodality due to coexistence of spherical and deformed mass symmetric fission modes.

Advanced driving assistance system (ADAS) is an electronic system that helps the driver navigate roads safely. A typical ADAS, however, is suited to specific brands of vehicle and, due to proprietary restrictions, has non-extendable features. Project CASA is an alternative, low-cost generic ADAS. It is an app deployable on smartphone or tablet. The real-time data needed by the app to make sense of its environment are stored in the vehicle or on the cloud, and are accessible as web services. They are used to determine the current driving context, and, if needed, decide actions to prevent an accident or keep road navigation safe. Project CASA is an undertaking of a consortium of industrial and academic partners. A use case scenario is tested in the laboratory (virtual) and on the road (actual) to validate the appropriateness of CASA. It is a contribution to safe driving. CASA’s contribution also lies in its approach in the semantic modeling of the context of the environment, the vehicle and the driver, and on the modeling of rules for fusion of data and fission process yielding an action to be implemented. In addition, CASA proposes a secured means of transmitting data using light, via light fidelity (LiFi), itself an alternative means of wireless vehicle–smartphone communication.

For many years at LLNL, we have been developing time-correlated neutron detection techniques and algorithms for applications such as Arms Control, Threat Detection and Nuclear Material Assay. Many of our techniques have been developed specifically for the relatively low efficiency (a few percent) inherent in man-portable systems. Historically, thermal neutron detectors (mainly ³He) were used, taking advantage of the high thermal neutron interaction cross-sections, but more recently we have been investigating the use of fast neutron detection with liquid scintillators, inorganic crystals, and in the near future, pulse-shape discriminating plastics that respond over 1000 times faster (nanoseconds versus tens of microseconds) than thermal neutron detectors. Fast neutron detection offers considerable advantages, since the inherent nanosecond production timescales of fission and neutron-induced fission are preserved and measured instead of being lost in the thermalization of thermal neutron detectors. We are now applying fast neutron technology to the safeguards regime in the form of high efficiency counters. Faster detector response times and sensitivity to neutron momentum show promise in measuring, differentiating, and assaying samples that have modest to very high count rates, as well as mixed neutron sources (e.g., Pu oxide or Mixed Cm and Pu). Here we report on measured results with our existing liquid scintillator array and promote the design of a nuclear material assay system that incorporates fast neutron detection, including the surprising result that fast liquid scintillator becomes competitive and even surpasses the precision of ³He counters measuring correlated pairs in modest (kg) samples of plutonium.