Fusion Probability Research Articles

Synthesis and decay process of superheavy nuclei with Z=119-122 via hot-fusion reactions

In this research article attempts have been made to calculate the superheavy-nuclei synthesis characteristics including, the potential energy parameters, fusion probability, fusion and evaporation residue (ER) cross sections as well as, decay properties of compound nucleus and the residue nuclei formation probability for elements with Z=119-122 by using the hot-fusion reactions. It is concluded that, although a selection of double magic projectiles such as 48Ca with high binding energy, simplifies the calculations significantly due to spherical symmetric shape of the projectile, resulting in high evaporation residue cross section, unfortunately, nuclei with $ Z > 98$ do not exist in quantities sufficient for constructing targets for the hot-fusion reactions. Therefore, practically our selection is fusion reactions with titanium projectile because the mass production of target nuclei for experimental purposes is more feasible. Based upon our findings, it is necessary, for new superheavy-nuclei production with $ Z > 119$ , to use neutron-rich projectiles and target nuclei. Finally, the maximal evaporation residue cross sections for the synthesis of superheavy elements with Z=119-122 have been calculated and compared with the previously founded ones in the literature.

Importance of lifetime effects in breakup and suppression of complete fusion in reactions of weakly bound nuclei

Complete fusion cross sections in collisions of light, weakly bound nuclei and high Z targets show above-barrier suppression of complete fusion. This has been interpreted as resulting from breakup of the weakly bound nucleus prior to reaching the fusion barrier, reducing the probability of complete fusion. This paper investigates how these conclusions are affected by lifetimes of the resonant states that are populated prior to breakup. If the mean life of a populated resonance is much longer than the fusion timescale, then its breakup cannot suppress complete fusion. For short-lived resonances, the situation is more complex. This work includes the mean life of the short-lived 2+ resonance in 8Be in classical dynamical model calculations to determine its effect on energy and angular correlations of the breakup fragments and on predictions of fusion suppression. Coincidence measurements of breakup fragments produced in reactions of 9Be with 144Sm, 168Er, 186W, 196Pt, 208Pb and 209Bi at energies below the barrier are re-analysed. Predictions of breakup observables and of complete and incomplete fusion at energies above the fusion barrier are made using the classical dynamical simulation code PLATYPUS, modified to include the lifetimes of short-lived resonant states. The agreement of the breakup observables is improved when lifetime effects are included. The predicted suppression of complete fusion due to breakup is nearly independent of Z, with an average value of 9%, below the experimentally determined fusion suppression of 30% in these systems. This more realistic treatment of breakup leads to the conclusion that the suppression of complete fusion cannot be fully explained by breakup prior to reaching the fusion barrier. Other mechanisms that can suppress complete fusion must be investigated. A candidate is cluster transfer that produces the same nuclei as incomplete fusion.

Reconstitution of Human Ion Channels into Solvent-free Lipid Bilayers Enhanced by Centrifugal Forces

Artificially formed bilayer lipid membranes (BLMs) provide well-defined systems for functional analyses of various membrane proteins, including ion channels. However, difficulties associated with the integration of membrane proteins into BLMs limit the experimental efficiency and usefulness of such BLM reconstitution systems. Here, we report on the use of centrifugation to more efficiently reconstitute human ion channels in solvent-free BLMs. The method improves the probability of membrane fusion. Membrane vesicles containing the human ether-a-go-go-related gene (hERG) channel, the human cardiac sodium channel (Nav1.5), and the human GABAA receptor (GABAAR) channel were formed, and the functional reconstitution of the channels into BLMs via vesicle fusion was investigated. Ion channel currents were recorded in 67% of the BLMs that were centrifuged with membrane vesicles under appropriate centrifugal conditions (14–55 × g). The characteristic channel properties were retained for hERG, Nav1.5, and GABAAR channels after centrifugal incorporation into the BLMs. A comparison of the centrifugal force with reported values for the fusion force revealed that a centrifugal enhancement in vesicle fusion was attained, not by accelerating the fusion process but by accelerating the delivery of membrane vesicles to the surface of the BLMs, which led to an increase in the number of membrane vesicles that were available for fusion. Our method for enhancing the probability of vesicle fusion promises to dramatically increase the experimental efficiency of BLM reconstitution systems, leading to the realization of a BLM-based, high-throughput platform for functional assays of various membrane proteins.

Direct observation of intermediate states in model membrane fusion.

We introduce a novel assay for membrane fusion of solid supported membranes on silica beads and on coverslips. Fusion of the lipid bilayers is induced by bringing an optically trapped bead in contact with the coverslip surface while observing the bead’s thermal motion with microsecond temporal and nanometer spatial resolution using a three-dimensional position detector. The probability of fusion is controlled by the membrane tension on the particle. We show that the progression of fusion can be monitored by changes in the three-dimensional position histograms of the bead and in its rate of diffusion. We were able to observe all fusion intermediates including transient fusion, formation of a stalk, hemifusion and the completion of a fusion pore. Fusion intermediates are characterized by axial but not lateral confinement of the motion of the bead and independently by the change of its rate of diffusion due to the additional drag from the stalk-like connection between the two membranes. The detailed information provided by this assay makes it ideally suited for studies of early events in pure lipid bilayer fusion or fusion assisted by fusogenic molecules.

Variable priming of a docked synaptic vesicle

The priming of a docked synaptic vesicle determines the probability of its membrane (VM) fusing with the presynaptic membrane (PM) when a nerve impulse arrives. To gain insight into the nature of priming, we searched by electron tomography for structural relationships correlated with fusion probability at active zones of axon terminals at frog neuromuscular junctions. For terminals fixed at rest, the contact area between the VM of docked vesicles and PM varied >10-fold with a normal distribution. There was no merging of the membranes. For terminals fixed during repetitive evoked synaptic transmission, the normal distribution of contact areas was shifted to the left, due in part to a decreased number of large contact areas, and there was a subpopulation of large contact areas where the membranes were hemifused, an intermediate preceding complete fusion. Thus, fusion probability of a docked vesicle is related to the extent of its VM-PM contact area. For terminals fixed 1 h after activity, the distribution of contact areas recovered to that at rest, indicating the extent of a VM-PM contact area is dynamic and in equilibrium. The extent of VM-PM contact areas in resting terminals correlated with eccentricity in vesicle shape caused by force toward the PM and with shortness of active zone material macromolecules linking vesicles to PM components, some thought to include Ca(2+) channels. We propose that priming is a variable continuum of events imposing variable fusion probability on each vesicle and is regulated by force-generating shortening of active zone material macromolecules in dynamic equilibrium.

Synapsin Null Increases Calcium Sensitivity of Vesicle Fusion and Alter Short-Term Synaptic Memory at Drosophila NMJ

The availability of synaptic vesicles (SVs) and their timing for fusion are critical for neurotransmitter release and neural communication. Synapsins (Syn) are abundant phosphoproteins associated reversibly with SVs and cytoskeleton. Syn is highly conserved in animal kingdom and is thought to regulate SVs trafficking and short-term plasticity. Syn function compromises learning and memory, however, its role in synaptic transmission is still under investigation. Here we analyzed Syn null by voltage-clamp recording of synaptic transmission at Drosophila glutamatergic model. We found that Syn null increases the probability of SV fusion by decreasing the sensitivity to calcium. In addition, Syn null increases asynchronous release, alters short-term plasticity and synaptic memory. A use-dependent model for neurotransmission induced by high-frequency nerve activity and a masked plasticity under depression is discussed.

Characterizing the mechanism(s) of heavy element synthesis reactions

A review of the current state of our understanding of complete fusion reaction mechanisms is presented, from the perspective of an experimentalist. For complete fusion reactions, the overall uncertainties in predicting heavy element synthesis cross sections are examined in terms of the uncertainties associated with the calculations of capture cross sections, fusion probabilities and survival probabilities.

Exploring dissipative processes at high angular momentum in58Ni+60Ni reactions

Current coupled channels (CC) models treat fusion as a coherent quantum-mechanical process, in which coupling between the collective states of the colliding nuclei influences the probability of fusion in near-barrier reactions. While CC models have been used to successfully describe many experimental fusion barrier distribution (BD) measurements, the CC approach has failed in the notable case of 16 O+208 Pb. The reason for this is poorly understood; however, it has been postulated that dissipative processes may play a role. Traditional BD experiments can only probe the physics of fusion for collisions at the top of the Coulomb barrier (L = 0ħ). In this work, we will present results using a novel method of probing dissipative processes inside the Coulomb barrier. The method exploits the predicted sharp onset of fission at L ~ 60ħ for reactions forming compound nuclei with A Ni+60 Ni reaction at a range of energies, in order to explore dissipative processes at high angular momentum. In this reaction, deep inelastic processes have been found to set in before the onset fission at high angular momentum following fusion. The results will be discussed in relation to the need for a dynamical model of fusion.

Heavy-ion fusion probability and nuclear fission rate in a quantum non-ohmic environment

Heavy-ion fusion probability and nuclear fission rate in a quantum non-ohmic environment

Fusion and quasi-fission dynamics in nearly-symmetric reactions

Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics (ImQMD) model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the stability of an individual nucleus and the description of fusion cross sections at energies near the Coulomb barrier can be further improved. Simultaneously, the quasi-fission process in $^{154}$Sm+$^{160}$Gd is also investigated with the microscopic dynamics model for the first time. We find that at energies above the Bass barrier, the fusion probability is smaller than $10^{-5}$ for this reaction, and the nuclear contact-time is generally smaller than $1500$ fm/c. From the central collisions of Sm+Gd, the neutron-rich fragments such as $^{164,165}$Gd, $^{192}$W can be produced in the ImQMD simulations, which implies that the quasi-fission reaction could be an alternative way to synthesize new neutron-rich heavy nuclei.

Relaxation times and modes of disturbed aggregate distribution in micellar solutions with fusion and fission of micelles.

We have performed direct numerical calculations of the kinetics of relaxation in the system of surfactant spherical micelles under joint action of the molecular mechanism with capture and emission of individual surfactant molecules by molecular aggregates and the mechanism of fusion and fission of the aggregates. As a basis, we have taken the difference equations of aggregation and fragmentation in the form of the generalized kinetic Smoluchowski equations for aggregate concentrations. The calculations have been made with using the droplet model of molecular surfactant aggregates and two modified Smoluchowski models for the coefficients of aggregate-monomer and aggregate-aggregate fusions which take into account the effects of the aggregate size and presence of hydrophobic spots on the aggregate surface. A full set of relaxation times and corresponding relaxation modes for nonequilibrium aggregate distribution in the aggregation number has been found. The dependencies of these relaxation times and modes on the total concentration of surfactant in the solution and the special parameter controlling the probability of fusion in collisions of micelles with other micelles have been studied.

Isotopic dependence of superheavy nuclear production in hot fusion reactions

The dependence of the evaporation residue cross section (ERCS)'s ability to produce superheavy nuclei (SHN) on the isospin of colliding nuclei is analyzed within the dinuclear system concept. ERCSs are discussed in detail and compared with existing experimental data. The fusion probabilities and surviving probabilities depend sensitively on the neutron numbers of the target and projectile nuclei. In most cases a neutron excess in the system can increase the producing cross section of a new nuclide of SHN. Some predicted ERCSs for the new isotopes of SHN were found to be as large as about 1--8 pb, which is large enough to be realized experimentally with the current existing technology. Element 120 may be produced by $^{50}\mathrm{Ti}+^{251,252}\mathrm{Cf}$, with the ERCS being about 0.03 pb, and element 119 may be produced by the reaction channel $^{50}\mathrm{Ti}+^{248,249}\mathrm{Bk}$, with the ERCS being about 0.1 pb via $3n$ and $4n$ emission channels, respectively. Radioactive projectiles are not much more favorable in comparison to stable projectiles.

The more pieces, the better the puzzle: sperm concentration increases gametic compatibility.

The genetic benefits individuals receive from mate choice have been the focus of numerous studies, with several showing support for both intrinsic genetic benefits and compatibility effects on fertilization success and offspring viability. However, the robustness of these effects have rarely been tested across an ecologically relevant environmental gradient. In particular, sperm environment is a crucial factor determining fertilization success in many species, especially those with external fertilization. Here, we test the importance of sperm environment in mediating compatibility-based selection on fertilization using a factorial breeding design. We detected a significant intrinsic male effect on fertilization success at only one of four sperm concentrations. Compatibility effects were significant at the two highest sperm concentrations and, interestingly, the magnitude of the compatibility effect consistently increased with sperm concentration. This suggests that females are able to modify the probability of sperm-egg fusion as the amount of sperm available increases.

A Collision and Reaction Model of Feature Fusion: Mechanism and Realization

Duplicate data must be properly handled in the process of intelligent search, surveillance, and tracking. To better detect and fuse this data, the authors take a new perspective on feature fusion based on the and reaction' mechanism of data objects. This mechanism can greatly facilitate differentiating duplicate and nonduplicate data in the fusion (reaction) probability. With this perspective, the fusion probability of a feature sample in a dataset is the cumulative effect of the microscopic collision (interaction) results between this sample and other samples. The operations on duplicate detection and feature fusion depend on the fusion probability and are finally realized when the collision process is finished. This new quantum-inspired feature fusion model gives interesting experimental results and could have great implications for some intelligent systems.

An experimentalist’s view of the uncertainties in understanding heavy element synthesis

The overall uncertainties in predicting heavy element synthesis cross sections are examined in terms of the uncertainties associated with the calculations of capture cross sections, fusion probabilities and survival probabilities. The values of the capture cross sections are known within a factor of two, the uncertainty in the values of the survival probabilities is no less than an order of magnitude with similar uncertainties in the fusion probabilities. Canceling errors may reduce the uncertainty in the overall predicted cross sections although for the heaviest nuclei (Z = 119 -120), the uncertainties in the predicted cross sections are a few orders of magnitude.

Erratum: Fusion probability in heavy nuclei [Phys. Rev. C91, 034619 (2015)

Erratum: Fusion probability in heavy nuclei [Phys. Rev. C<b>91</b>, 034619 (2015)

Effects of entrance channels on the evaporation residue yields in reactions leading to theTh220compound nucleus

The evaporation residue yields from the compound nuclei $^{220}\mathrm{Th}$ formed in the $^{16}\mathrm{O}+^{204}\mathrm{Pb}, ^{40}\mathrm{Ar}+^{180}\mathrm{Hf}, ^{82}\mathrm{Se}+^{138}\mathrm{Ba}$, and $^{124}\mathrm{Sn}+^{96}\mathrm{Zr}$ reactions are analyzed to study the entrance channel effects by comparison of the capture, fusion, and evaporation residue cross sections calculated by the combined dinuclear system (DNS) and advanced statistical models. The difference between evaporation residue (ER) cross sections can be related to the stages of compound nucleus formation and/or its survival against fission. The sensitivity of both stages in the evolution of the DNS up to the evaporation residue formation to the angular momentum of DNS is studied. The difference between fusion excitation functions is explained by the hindrance to complete fusion due to the larger intrinsic fusion barrier ${B}_{\mathrm{fus}}^{*}$ for the transformation of the DNS into a compound nucleus and the increase of the quasifission contribution due to the decreasing of the quasifission barrier ${B}_{\mathrm{qf}}$ as a function of the angular momentum. The largest value of the ER residue yields in the very mass asymmetric $^{16}\mathrm{O}+^{204}\mathrm{Pb}$ reaction is related to the large fusion probability and to the relatively low threshold of the excitation energy of the compound nucleus. Due to the large threshold of the excitation energy (35 MeV) of the $^{40}\mathrm{Ar}+^{180}\mathrm{Hf}$ reaction, it produces ER yields less than the almost mass symmetric $^{82}\mathrm{Se}+^{138}\mathrm{Ba}$ reaction having the lowest threshold value (12 MeV).

GABAB receptor deficiency causes failure of neuronal homeostasis in hippocampal networks

Stabilization of neuronal activity by homeostatic control systems is fundamental for proper functioning of neural circuits. Failure in neuronal homeostasis has been hypothesized to underlie common pathophysiological mechanisms in a variety of brain disorders. However, the key molecules regulating homeostasis in central mammalian neural circuits remain obscure. Here, we show that selective inactivation of GABAB, but not GABA(A), receptors impairs firing rate homeostasis by disrupting synaptic homeostatic plasticity in hippocampal networks. Pharmacological GABA(B) receptor (GABA(B)R) blockade or genetic deletion of the GB(1a) receptor subunit disrupts homeostatic regulation of synaptic vesicle release. GABA(B)Rs mediate adaptive presynaptic enhancement to neuronal inactivity by two principle mechanisms: First, neuronal silencing promotes syntaxin-1 switch from a closed to an open conformation to accelerate soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex assembly, and second, it boosts spike-evoked presynaptic calcium flux. In both cases, neuronal inactivity removes tonic block imposed by the presynaptic, GB(1a)-containing receptors on syntaxin-1 opening and calcium entry to enhance probability of vesicle fusion. We identified the GB(1a) intracellular domain essential for the presynaptic homeostatic response by tuning intermolecular interactions among the receptor, syntaxin-1, and the Ca(V)2.2 channel. The presynaptic adaptations were accompanied by scaling of excitatory quantal amplitude via the postsynaptic, GB(1b)-containing receptors. Thus, GABA(B)Rs sense chronic perturbations in GABA levels and transduce it to homeostatic changes in synaptic strength. Our results reveal a novel role for GABA(B)R as a key regulator of population firing stability and propose that disruption of homeostatic synaptic plasticity may underlie seizure's persistence in the absence of functional GABA(B)Rs.

Modified fusion probability by reflection boundary**Supported by National Natural Science Foundation of China (11175021) and Specialized Research Fund for the Doctoral Program of Higher Education (20120003110025)

We investigate the time-dependent probability for a Brownian particle passing over the barrier to stay at a metastable potential pocket against escaping over the barrier. This is related to the whole fusion-fission dynamical process and can be called the reverse Kramers problem. By the passing probability over the saddle point of an inverse harmonic potential multiplying the exponential decay factor of a particle in the metastable potential, we present an approximate expression for the modified passing probability over the barrier, in which the effect of the reflection boundary of the potential is taken into account. Our analytical result and Langevin Monte-Carlo simulation show that the probability of passing and against escaping over the barrier is a non-monotonous function of time and its maximal value is less than the stationary result of the passing probability over the saddle point of an inverse harmonic potential.

Reduced quasifission competition in fusion reactions forming neutron-rich heavy elements

Measurements of mass-angle distributions (MADs) for Cr + W reactions, providing a wide range in the neutron-to-proton ratio of the compound system, ${(N/Z)}_{\mathrm{CN}}$, have allowed for the dependence of quasifission on the ${(N/Z)}_{\mathrm{CN}}$ to be determined in a model-independent way. Previous experimental and theoretical studies had produced conflicting conclusions. The experimental MADs reveal an increase in contact time and mass evolution of the quasifission fragments with increasing ${(N/Z)}_{\mathrm{CN}}$, which is indicative of an increase in the fusion probability. The experimental results are in agreement with microscopic time-dependent Hartree-Fock calculations of the quasifission process. The experimental and theoretical results favor the use of the most neutron-rich projectiles and targets for the production of heavy and superheavy nuclei.