Fission Process Research Articles

Preformation probability of light charged particles emitted equatorially in ternary fission of Cf252

We investigate the preformation probability of the light particle that formed in the preliminary stage of the ternary fission process of the $^{252}\mathrm{Cf}$ nucleus. Considering the equatorial cluster tripartition kinematics, the relative yields of the ternary fission channels with $^{4,6}\mathrm{He}, ^{10}\mathrm{Be}$ and $^{14}\mathrm{C}$ as light third nucleus, are calculated. We use the Wentzel-Kramers-Brillouin approximation to calculate the penetrability of the different nuclei involved in the ternary fission process, based on microscopic Skyrme potentials. The obtained results indicate the optimum total excitation energy of the heavy nuclei produced in the $\ensuremath{\alpha}$ ternary fission channels to be within the range of 3--4 MeV. The estimated $\ensuremath{\alpha}$-preformation probability corresponding to this range is comparable with that estimated for the spontaneous $\ensuremath{\alpha}$ decays of the participating heavy nuclei. While the extracted preformation probability at excitation energy less than its indicated optimum values exhibits unphysical large values, the calculations based on the higher excitation energies indicate extremely small values. In the ternary fission process, the preformation probability of the emitted light particles heavier than the $\ensuremath{\alpha}$ particle exponentially decreases with increasing its mass number. A phenomenological expression is suggested based on the obtained results to estimate the preformation probability of an emitted cluster of a given mass number.

3D cyclorama for digital unrolling and visualisation of deformed tubes

Colonic crypts are tubular glands that multiply through a symmetric branching process called crypt fission. During the early stages of colorectal cancer, the normal fission process is disturbed, leading to asymmetrical branching or budding. The challenging shapes of the budding crypts make it difficult to prepare paraffin sections for conventional histology, resulting in colonic cross sections with crypts that are only partially visible. To study crypt budding in situ and in three dimensions (3D), we employ X-ray micro-computed tomography to image intact colons, and a new method we developed (3D cyclorama) to digitally unroll them. Here, we present, verify and validate our ‘3D cyclorama’ method that digitally unrolls deformed tubes of non-uniform thickness. It employs principles from electrostatics to reform the tube into a series of onion-like surfaces, which are mapped onto planar panoramic views. This enables the study of features extending over several layers of the tube’s depth, demonstrated here by two case studies: (i) microvilli in the human placenta and (ii) 3D-printed adhesive films for drug delivery. Our 3D cyclorama method can provide novel insights into a wide spectrum of applications where digital unrolling or flattening is necessary, including long bones, teeth roots and ancient scrolls.

Following nuclei through nucleosynthesis: A novel tracing technique

Astrophysical nucleosynthesis is a family of diverse processes by which atomic nuclei undergo nuclear reactions and decay to form new nuclei. The complex nature of nucleosynthesis, which can involve as many as tens of thousands of interactions between thousands of nuclei, makes it difficult to study any one of these interactions in isolation using standard approaches. In this work, we present a new technique, nucleosynthesis tracing, that we use to quantify the relative fraction of nuclear abundances that pass through individual nuclear reaction, decay, and fission processes at any point during nucleosynthesis. We apply this technique to study fission and ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay as they occur in the rapid neutron capture ($r$) process of nucleosynthesis.

Utilization of prompt gamma rays in gamma irradiation experiments

A new technique was introduced in this study to utilize the prompt gamma rays, that generated from the fission process, in gamma irradiation experiments. The method de- pends on utilizing the difference of the attenuation effect of water on neutrons

Mitostasis, Calcium and Free Radicals in Health, Aging and Neurodegeneration.

Mitochondria play key roles in ATP supply, calcium homeostasis, redox balance control and apoptosis, which in neurons are fundamental for neurotransmission and to allow synaptic plasticity. Their functional integrity is maintained by mitostasis, a process that involves mitochondrial transport, anchoring, fusion and fission processes regulated by different signaling pathways but mainly by the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). PGC-1α also favors Ca2+ homeostasis, reduces oxidative stress, modulates inflammatory processes and mobilizes mitochondria to where they are needed. To achieve their functions, mitochondria are tightly connected to the endoplasmic reticulum (ER) through specialized structures of the ER termed mitochondria-associated membranes (MAMs), which facilitate the communication between these two organelles mainly to aim Ca2+ buffering. Alterations in mitochondrial activity enhance reactive oxygen species (ROS) production, disturbing the physiological metabolism and causing cell damage. Furthermore, cytosolic Ca2+ overload results in an increase in mitochondrial Ca2+, resulting in mitochondrial dysfunction and the induction of mitochondrial permeability transition pore (mPTP) opening, leading to mitochondrial swelling and cell death through apoptosis as demonstrated in several neuropathologies. In summary, mitochondrial homeostasis is critical to maintain neuronal function; in fact, their regulation aims to improve neuronal viability and to protect against aging and neurodegenerative diseases.

Novel Insights and Current Evidence for Mechanisms of Atherosclerosis: Mitochondrial Dynamics as a Potential Therapeutic Target

Cardiovascular disease (CVD) is the main cause of death worldwide. Atherosclerosis is the underlying pathological basis of CVD. Mitochondrial homeostasis is maintained through the dynamic processes of fusion and fission. Mitochondria are involved in many cellular processes, such as steroid biosynthesis, calcium homeostasis, immune cell activation, redox signaling, apoptosis, and inflammation, among others. Under stress conditions, mitochondrial dynamics, mitochondrial cristae remodeling, and mitochondrial ROS (mitoROS) production increase, mitochondrial membrane potential (MMP) decreases, calcium homeostasis is imbalanced, and mitochondrial permeability transition pore open (mPTP) and release of mitochondrial DNA (mtDNA) are activated. mtDNA recognized by TLR9 can lead to NF-κB pathway activation and pro-inflammatory factor expression. At the same time, TLR9 can also activate NLRP3 inflammasomes and release interleukin, an event that eventually leads to tissue damage and inflammatory responses. In addition, mitochondrial dysfunction may amplify the activation of NLRP3 through the production of mitochondrial ROS, which together aggravate accumulating mitochondrial damage. In addition, mtDNA defects or gene mutation can lead to mitochondrial oxidative stress. Finally, obesity, diabetes, hypertension and aging are risk factors for the progression of CVD, which are closely related to mitochondrial dynamics. Mitochondrial dynamics may represent a new target in the treatment of atherosclerosis. Antioxidants, mitochondrial inhibitors, and various new therapies to correct mitochondrial dysfunction represent a few directions for future research on therapeutic intervention and amelioration of atherosclerosis.

The fractional analysis of fusion and fission process in plasma physics

The space-time fractional non-linear Phi-4 equation is a significant equation to describes the fission and fusion process that ensued in chemical kinematics, solid-state physics, astrophysical fusion plasma, plasma physics, and electromagnetic interactions, etc. The Phi-4 non-linear partial differential equation is reshaped utilizing the three different fractional-order derivatives and constructed transformations corresponding to every fractional-order derivative to convert the partial differential equation into an ordinary differential equation. A new extended direct algebraic equation method was successfully applied to extract the solitons solutions. The solitons solutions are developed with the exponential, trigonometric, rational, and hyperbolic functions including different unknown constant parameters. The graphical interpretations of obtained solutions are also depicted by allocating the feasible values to unknown constant parameters. The proposed scheme is an effective and functional scientific technique to investigate different fractional systems and models in engineering and physics referenced to real physical problems.

Cascade exciton model analysis of energetic pion-induced fission of heavy nuclei: Target mass and projectile energy dependence

A data bank of negative and positive (80–1665[Formula: see text]MeV) pion-induced experimental fission cross-sections of heavy nuclei from 119Sn to 238U is compiled using present results and published data from the literature. Corresponding calculations of fission cross-sections, using the cascade exciton model (CEM) are also included in the compilation. Fission cross-sections compiled in the data bank are examined critically. Mass and energy dependences of fission cross-sections are analyzed. Fission cross-sections of 238U targets are the highest and scale down approximately, for other targets studied, with fissility, [Formula: see text]. In the fissility expression, [Formula: see text] and [Formula: see text] are atomic and mass numbers of the target while [Formula: see text] refer to positive and negative pion projectiles. The presented data bank is of interest for students and researchers involved in the investigation of energetic light particle-induced fission of heavy nuclei. Nuclear fission of heavy nuclei has been classified into three regimes. Phenomenological discussion of the fission process is also given.

Temperature Tuning of Coherent Mixing between States Driving Singlet Fission in a Spiro-Fused Terrylenediimide Dimer.

The excited-state dynamics of a spiro-fused terrylene-3,4:11,12-bis(dicarboximide) (TDI) dimer (sTDI2) in toluene and 2-methyltetrahydrofuran (mTHF) were investigated as a function of temperature using femtosecond- and nanosecond-transient absorption spectroscopy, as well as two-dimensional electronic spectroscopy. The spiro conjugation and the corresponding geometry of this compound guarantee a short intermonomer distance along with a partial orbital overlap between the orthogonal TDI π-electron systems, providing electronic coupling between the TDIs. Photoexcitation of sTDI2 in toluene, a low dielectric solvent, at 295 K, results in the ultrafast formation of a state composed of a coherent mixture of singlet 1(S1S0), multiexciton 1(T1T1), and charge-transfer (CT) electronic characters. This mixed species decays to decorrelated triplet states on the nanosecond timescale, completing the process of intramolecular singlet fission (SF) in sTDI2. Upon decreasing the temperature from 295 to 200 K, the contribution of the 1(T1T1) state to the mixed species decreases concurrently with an increase in the CT state character. We attribute this behavior to the variation in the vibrational energy level alignment between the states comprising the mixture due to changes in the temperature and hence the local dielectric environment. In contrast, photoexcitation of sTDI2 in more polar mTHF at 295 K results in the formation of a mixed singlet and CT state before undergoing symmetry-breaking charge separation, owing to the increased stabilization of the CT state in the medium. However, in glassy mTHF at 85 K, photoexcited sTDI2 exhibits discernible multiexciton character, comparable to that observed in toluene at 200 K, which we rationalize by the similarity of the dielectric constants under these two sets of conditions. These observations of mixed states of varying diabatic contributions over the range of experimental conditions show that the temperature and the static dielectric constant can directly control the composition of the electronically mixed excited state of sTDI2 and thus the fate of the SF process.

Simulation of Time- and Frequency-Resolved Four-Wave-Mixing Signals at Finite Temperatures: A Thermo-Field Dynamics Approach

We propose a new approach to simulate four-wave-mixing signals of molecular systems at finite temperatures by combining the multiconfigurational Ehrenfest method with the thermo-field dynamics theory. In our approach, the four-time correlation functions at finite temperatures are mapped onto those at zero temperature in an enlarged Hilbert space with twice the vibrational degrees of freedom. As an illustration, we have simulated three multidimensional spectroscopic signals, time- and frequency-resolved fluorescence spectra, transient-absorption pump-probe spectra, and electronic two-dimensional (2D) spectra at finite temperatures, for a conical intersection-mediated singlet fission model of a rubrene crystal. It is shown that a detailed dynamical picture of the singlet fission process can be extracted from the three spectroscopic signals. An increasing temperature leads to lower intensities of the signals and broadened vibrational peaks, which can be attributed to faster singlet-triplet population transfer and stronger bath-induced electronic dephasing at higher temperatures.

A link between protein acetylation and mitochondrial dynamics under energy metabolism: A comprehensive overview.

Cells adjust mitochondrial morphologies to coordinate between the cellular demand for energy and the availability of resources. Mitochondrial morphology is regulated by the balance between two counteracting mitochondrial processes of fusion and fission. Fission and fusion are dynamic and reversible processes that depend on the coordination of a number of proteins and are primarily regulated by posttranslational modifications. In the mitochondria, more than 20% of proteins are acetylated in proteomic surveys, partly involved in the dynamic regulation of mitochondrial fusion and fission. This article focuses on the molecular mechanism of the mitochondrial dynamics of fusion and fission, and summarizes the related mechanisms and targets of mitochondrial protein acetylation to regulatethe mitochondrial dynamics of fusion and fission in energy metabolism.

(Invited) Advanced Concepts for Ultra-High Conversion Efficiency of Solar Photons into Photovoltaics and Solar Fuels Based on Semiconductor Nanostructures and Molecular Singlet Fissionajn

In order to utilize solar power for the production of solar electricity and solar fuels on a global scale, it is necessary to develop solar photon conversion systems that have an appropriate combination of very high efficiency (delivered watts/m2) and low capital cost ($/m2). One potential promising approach to attain high conversion efficiencies well above the Shockley-Queisser limit of 33% is to utilize the unique properties of semiconductor nanostructures (viz., quantum dots/rods/films) and singlet fission chromophores to control the relaxation dynamics of photogenerated carriers and photochemical excited states, respectively. The former process creates enhanced photocurrent through efficient photogenerated electron-hole pair multiplication (electron-hole pairs exist as excitons in size-quantized nanostructures), or enhanced photopotential through hot carrier transport, transfer, and extraction processes. The latter process of singlet fission generates two triplets from an excited singlet state. These fundamental dynamics in various bulk and nanoscale semiconductors and in molecular chromophores have been studied using transient absorption, photoluminescence, photocurrent and THz spectroscopy with fs to ns time resolution. The predictions that the generation of more than one electron-hole pair or exciton per absorbed photon would be an efficient process in nanostructures, and via singlet fission, have been confirmed in different classes of materials, molecules, and their architectures in photon conversion devices. Selected aspects of this work will be summarized and recent advances will be discussed, including the very remarkable and beneficial theoretical effects of combining MEG or singlet fission with solar concentration and controlling the thicknesses of the photoactive layers in a two-photon photoelectrosynthesis cell structure for solar fuels.

Atorvastatin reverses high cholesterol-induced cardiac remodelling and regulates mitochondrial quality-control in a cholesterol-independent manner: An experimental study.

Mitochondria are key regulators of cell fate, maintaining self-stability by a fine-tuned quality-control network including mitophagy, biogenesis, fission and fusion processes. Myocardial mitochondria can be impaired by hypercholesterolemia. Statins, such as atorvastatin, are considered thecornerstonein the management of hypercholesterolaemia primarily due to their marked cholesterol-lowering ability. The direct effect of atorvastatin on myocardial mitochondria remains unclear. We aimed to explore whether atorvastatin could attenuate myocardial mitochondrial defects induced by high cholesterol, and whether cycloastragenol, a potent telomerase activator, could be used as a potential complementary bioactive compound for obesity and hypercholesterolaemia treatment. We found that atorvastatin at a low dose (3mg/kg) did not reduce elevated serum cholesterol, but reversed cardiac remodelling and dysfunction in C57BL/6J mice fed with high-fat diet (HFD). Atorvastatin reversed the upregulated mitophagy, mitochondrial fission and fusion, accompanied by mitochondrial biogenesis activation in HFD-fed mice hearts. Mitochondrial structural impairments were attenuated by atorvastatin in HFD-fed mice and oxidized low-density lipoprotein (ox-LDL) exposed HL-1 cardiomyocytes. The depolarized mitochondrial membrane potential and increased mitochondrial oxygen consumption rates in ox-LDL exposed HL-1 cells were recovered by atorvastatin. Furthermore, atorvastatin co-treated with cycloastragenol had better effects on reducing body weight, improving cardiac remodelling and dysfunction, and protecting mitochondria in high cholesterol. Conclusively, low-dose atorvastatin exhibited a cholesterol-independent cardioprotective effect through improving the mitochondrial quality-control network and repairing mitochondrial ultrastructure in high cholesterol. Atorvastatin plus cycloastragenol supplement therapy has a better effect on treating obesity and hypercholesterolaemia.

Contribution of Massive Mitochondrial Fusion and Subsequent Fission in the Plant Life Cycle to the Integrity of the Mitochondrion and Its Genome.

Plant mitochondria have large genomes to house a small number of key genes. Most mitochondria do not contain a whole genome. Despite these latter characteristics, the mitochondrial genome is faithfully maternally inherited. To maintain the mitochondrial genes—so important for energy production—the fusion and fission of mitochondria are critical. Fission in plants is better understood than fusion, with the dynamin-related proteins (DRP 3A and 3B) driving the constriction of the mitochondrion. How the endoplasmic reticulum and the cytoskeleton are linked to the fission process is not yet fully understood. The fusion mechanism is less well understood, as obvious orthologues are not present. However, there is a recently described gene, MIRO2, that appears to have a significant role, as does the ER and cytoskeleton. Massive mitochondrial fusion (MMF or hyperfusion) plays a significant role in plants. MMF occurs at critical times of the life cycle, prior to flowering, in the enlarging zygote and at germination, mixing the cells’ mitochondrial population—the so-called “discontinuous whole”. MMF in particular aids genome repair, the conservation of critical genes and possibly gives an energy boost to important stages of the life cycle. MMF is also important in plant regeneration, an important component of plant biotechnology.

Rapid imaging of special nuclear materials for nuclear nonproliferation and terrorism prevention.

We introduce a neutron-gamma emission tomography (NGET) technique for rapid detection, three-dimensional imaging, and characterization of special nuclear materials like weapons-grade plutonium and uranium. The technique is adapted from fundamental nuclear physics research and represents a previously unexplored approach to the detection and imaging of small quantities of these materials. The method is demonstrated on a radiation portal monitor prototype system based on fast organic scintillators, measuring the characteristic fast time and energy correlations between particles emitted in nuclear fission processes. The use of these correlations in real time in conjunction with modern machine learning techniques provides unprecedented imaging efficiency and high spatial resolution. This imaging modality addresses global security threats from terrorism and the proliferation of nuclear weapons. It also provides enhanced capabilities for addressing different nuclear accident scenarios and for environmental radiological surveying.

Singlet Fission in Dideuterated Tetracene and Pentacene

AbstractThe impact of molecular vibrations on singlet fission, which is the spontaneous fission of a singlet exciton into two triplet excitons, is studied using ultrafast optical spectroscopy for the prototypical singlet fission chromophores tetracene and pentacene. We modify the frequency of intramolecular vibrations by deuteration, without impacting thin film structure and molecular arrangement, and study the resulting changes in exo‐ and endothermic singlet fission rates by comparing the deuterated and parent chromophores. We find that changes in the frequency of the C−C deformation modes of Δω=6 cm−1 and the occurrence of C−D vibrational modes do not lead to significant modifications in the singlet fission time constants. We conclude that the changes in the frequency of phonon modes induced by deuteration are too small to significantly impact the electron–phonon coupling that drives the singlet fission process.

Spent Nuclear Fuel Incineration by Fusion-Driven Liquid Transmutator Operated in Real Time by Laser

We introduce a concept of laser-generated neutrons to transmute transuranic elements separated from spent nuclear fuel (SNF) and dissolved in a molten salt to form a subcritical core whose liquid state allows and facilitates safety, laser irradiation, and monitoring of chemical and physical properties. In this transmutation concept (the transmutator), the neutrons are generated via beam-target fusion whereas the beam is created by laser irradiation of nanometric foils through the Coherent Acceleration of Ions by Laser (CAIL) process. This relatively low deuteron energy is catapulted by fusion and eventually by secondary fission processes. The combination of the use of molten salt and laser allows us to introduce rapid feedback control of the system’s operation. The transmutator is an integral part of the partitioning and transmutation concept whereby the radiotoxicity of SNF is significantly reduced together with the required storage duration and volume. To enable this transmutator, we introduce integrated ideas and processes in the areas of lasers, neutronics, first-wall material, and chemistry.

On Gaussian curvature and membrane fission

We propose a three-dimensional mathematical model to describe dynamical processes of membrane fission. The model is based on a phase field equation that includes the Gaussian curvature contribution to the bending energy. With the addition of the Gaussian curvature energy term numerical simulations agree with the predictions that tubular shapes can break down into multiple vesicles. A dispersion relation obtained with linear analysis predicts the wavelength of the instability and the number of formed vesicles. Finally, a membrane shape diagram is obtained for the different Gaussian and bending modulus, showing different shape regimes.

A Single Dose of Exercise Initiates Corrective Mitochondrial Plasticity in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common life-limiting muscular dystrophy in adults. Abnormal mitochondrial function and dynamics have been observed in DM1 patient derived cells, which likely exacerbates the muscle pathology in DM1. Exercise is safe, low-cost, and accessible medicine that reaps robust benefits to mitochondrial biology. However, in DM1 muscle, in vivo assessments of mitochondrial dynamics and mitophagy, as well as the effects of exercise therein, remain unexamined. Therefore, this study aims to further elucidate mitochondrial properties in a mouse model of DM1 (HSALR) and examine the mitochondrial response following an acute bout of exercise. Both wild-type (WT) and HSALR mice performed a progressive, vigorous bout of exercise on a treadmill until the inability to continue running was objectively determined. Muscle samples were collected at rest and at various timepoints following exercise. At rest, phosphorylated dynamin-related protein 1 (p-DRP1Ser616), total DRP1 and Parkin levels were elevated (p < 0.05) in HSALR mice compared to WT. Furthermore, the mitofusin-2 (MFN2)-to-DRP ratio was significantly lower in HSALR animals relative to their WT counterparts. Exercise capacity was lower (p < 0.05) in HSALR mice compared to WT. Immediately following exercise, p-DRP1Ser616 levels were significantly increased in WT animals but returned to the resting state at 3 hours post-exercise. In contrast, HSALR showed elevated (p < 0.05) p-DRP1Ser616 until 3 hours post-exercise before returning to basal levels at 12 hours. Mitochondrial fission 1 (Fis1) protein content significantly increased 3 hours post-exercise in WT animals and 12 hours post-exercise in the HSALR group. MFN2 content was augmented (p < 0.05) immediately following exercise and remained elevated up to 24 hours in HSALR mice only, thus, restoring the MFN2-to-DRP1 ratio. Lastly, fission and mitophagy related mRNA transcripts were blunted immediately and 3 hours (p < 0.05) following exercise while the transcription of fusion related genes was augmented (p < 0.05). In contrast, the expression of mitophagy related genes was significantly increased 12 and 24 hours following the exercise bout. Collectively, these data provide further evidence for mitochondrial dysfunction within DM1 biology. An imbalance in fusion and fission processes could greatly diminish mitochondrial function, which could in turn accelerate skeletal muscle atrophy. Exercise may be a promising intervention to correct the imbalance in mitochondrial dynamics and augment overall mitochondrial function within DM1 muscle.

Budding and Fission of Nanovesicles Induced by Membrane Adsorption of Small Solutes.

Membrane budding and fission are essential cellular processes that produce new membrane compartments during cell and organelle division, for intracellular vesicle trafficking as well as during endo- and exocytosis. Such morphological transformations have also been observed for giant lipid vesicles with a size of many micrometers. Here, we report budding and fission processes of lipid nanovesicles with a size below 50 nm. We use coarse-grained molecular dynamics simulations, by which we can visualize the morphological transformations of individual vesicles. The budding and fission processes are induced by low concentrations of small solutes that absorb onto the outer leaflets of the vesicle membranes. In addition to the solute concentration, we identify the solvent conditions as a second key parameter for these processes. For good solvent conditions, the budding of a nanovesicle can be controlled by reducing the vesicle volume for constant solute concentration or by increasing the solute concentration for constant vesicle volume. After the budding process is completed, the budded vesicle consists of two membrane subcompartments which are connected by a closed membrane neck. The budding process is reversible as we demonstrate explicitly by reopening the closed neck. For poor solvent conditions, on the other hand, we observe two unexpected morphological transformations of nanovesicles. Close to the binodal line, at which the aqueous solution undergoes phase separation, the vesicle exhibits recurrent shape changes with closed and open membrane necks, reminiscent of flickering fusion pores (kiss-and-run) as observed for synaptic vesicles. As we approach the binodal line even closer, the recurrent shape changes are truncated by the fission of the membrane neck which leads to the division of the nanovesicle into two daughter vesicles. In this way, our simulations reveal a nanoscale mechanism for the budding and fission of nanovesicles, a mechanism that arises from the interplay between membrane elasticity and solute-mediated membrane adhesion.