Fission Ratio Research Articles

Metformin protects against diclofenac-induced toxicity in primary rat hepatocytes by preserving mitochondrial integrity via a pathway involving EPAC

Background and purposeIt has been shown that the antidiabetic drug metformin protects hepatocytes against toxicity by various stressors. Chronic or excessive consumption of diclofenac (DF) - a pain-relieving drug, leads to drug-induced liver injury via a mechanism involving mitochondrial damage and ultimately apoptotic death of hepatocytes. However, whether metformin protects against DF-induced toxicity is unknown. Recently, it was also shown that cAMP elevation is protective against DF-induced apoptotic death in hepatocytes, a protective effect primarily involving the downstream cAMP effector EPAC and preservation of mitochondrial function. This study therefore aimed at investigating whether metformin protects against DF-induced toxicity via cAMP-EPACs. Experimental approachPrimary rat hepatocytes were exposed to 400 µmol/L DF. CE3F4 or ESI-O5 were used as EPAC-1 or 2 inhibitors respectively. Apoptosis was measured by caspase-3 activity and necrosis by Sytox green staining. Seahorse X96 assay was used to determine mitochondrial function. Mitochondrial reactive oxygen species (ROS) production was measured using MitoSox, mitochondrial MnSOD expression was determined by immunostaining and mitochondrial morphology (fusion and fission ratio) by 3D refractive index imaging. Key resultsMetformin (1 mmol/L) was protective against DF-induced apoptosis in hepatocytes. This protective effect was EPAC-dependent (mainly EPAC-2). Metformin restored mitochondrial morphology in an EPAC-independent manner. DF-induced mitochondrial dysfunction which was demonstrated by decreased oxygen consumption rate, an increased ROS production and a reduced MnSOD level, were all reversed by metformin in an EPAC-dependent manner. Conclusion and implicationsMetformin protects hepatocytes against DF-induced toxicity via cAMP-dependent EPAC-2.

Energy dissipation and suppression of capture cross sections in heavy ion reactions

Background: At energies above the capture barrier, coupled-channels (CC) calculations with a standard nuclear potential diffuseness (0.65 fm) increasingly overestimate experimental capture cross section as the charge product (${Z}_{1}{Z}_{2}$) of the colliding nuclei increases. It has been suggested this may be linked to energy dissipation outside the capture barrier.Purpose: We investigate quantitatively the role of energy dissipation in suppressing capture in heavy ion fusion reactions.Method: The yields of sequential fission, including that resulting from deep inelastic collisions, and of fission following capture were determined simultaneously for collisions of $^{18}\mathrm{O}, ^{30}\mathrm{Si}, ^{34}\mathrm{S}$, and $^{40}\mathrm{Ca}+^{232}\mathrm{Th}$ at a range of energies around the respective capture barriers.Results: The ratio of experimental to CC capture cross sections was found to decrease with increasing ${Z}_{1}{Z}_{2}$. Conversely, the ratio of sequential fission to capture-fission increased with increasing ${Z}_{1}{Z}_{2}$. The sum of sequential and capture fission agrees quite well with the CC cross sections.Conclusions: The experimental capture fission and sequential fission cross sections, and their comparison with CC calculations, give a consistent picture that the increase in density overlap at the capture barrier with increasing ${Z}_{1}{Z}_{2}$ of the colliding nuclei is correlated with increasing energy dissipative processes. These compete increasingly strongly with capture as the ${Z}_{1}{Z}_{2}$ of the reaction increases. For the $^{40}\mathrm{Ca}$ reaction, the total fission yield exceeds expectations from capture model calculations, indicating that deep inelastic processes occur both from trajectories that would have led to capture and also from more peripheral trajectories.

Transmutation efficiency of the spallation neutron target measured with the actinide sandwiches

We used actinide sandwiches composed of 233U, 235U, 236U, 238U, 237Np, 238Pu, and 239Pu isotopes to study the transmutation efficiency of the natural uranium spallation target Quinta bombarded with 660-MeV protons. The efficiency, defined as a ratio of fission to production, was determined by measuring simultaneously the production of transuranium isotopes via the (n, γ) and (n,xn) reactions, and fission incineration of their reaction products. For example, with the 238U–239Pu sandwich, measured was the production of 239Pu from 238U via the (n, γ) reaction, as well as 239Pu transmutation via fission. The efficiencies were measured using gamma spectroscopy. All the measured efficiencies were greater than 1.0, which demonstrates that the fast neutron spectrum at Quinta is highly suitable for actinide transmutation. Experimental results were compared with computer simulations employing the latest versions of the MCNP6 code and ENDF/B-VIII and JENDL/HE data libraries. A good agreement within one standard deviation was reached, which validates the utilized computation suite and shows that the suite is well capable of performing neutronic simulations related to actinide transmutation, spallation neutron sources and accelerator-driven systems.

Functional activity of mitochondria associated with cytoskeleton stability in the HEK293

Mitochondria are dynamic cellular organelles that provide the biological energy to the cell. The dynamic property of the mitochondria is associated with the cytoskeleton network in the cell. However, relationship is no clear identified between cytoskeleton instability and the functional activity of mitochondria in cell. This study is designed to assess the dynamic properties of the mitochondria, and specifically to observe whether they are associated with the cytoskeleton stability for the mitochondria’s functional activityWe prepared the cytoskeleton stability regulation model with the HEK293 cell line by vinorelbine which microtubule distributor and the cytoskeleton stabilizer as a taxol. We determined the optimal concentration of vinorelbine and taxol though cytotoxicity assay with the HEK293 cell line. Then, we analyzed the functional activity of the mitochondria depending on the microtubule instability. First, we undertook an observation of cell morphology under distributor or stabilizer. We analyzed the metabolic activity of the cell with the CCK and ATP productive assay. And we performed confocal live imaging for observation of mitochondria morphology in the cytoskeleton instable cells. We performed the reverse transcription polymer chain reaction for analysis of the mRNA expression in the cytoskeleton’s instable cells with Tau protein, Glut1 and GAPDH as the normalization marker.The vinorelbine treated cell shows dramatically changes with cell morphology compared with control. And the vinorelbine treated cell significantly increases the fission ratios of the mitochondria compared with the original form based on the confocal images. Microtubule instable cells significantly decreased the ATP’s productive ratios and the functional activity of the mitochondria. However, the cytoskeleton stabilizer as a taxol(0.01uM) combined with vinorelbine treated cells, shows recovery effect to cell morphology recovery effect like the control cells that were only treated with vinorebine. And taxol that was combined with vinorelbine treated cells significantly increased bioenergy product ratios and its functional activity compared with the vinorelbine.In conclusion, the dynamic mitochondrial motility might influence the microtubule stability in cells. Because, vinorelbine‐treated cells displayed destabilized microtubules, loss of motility and fission formation of mitochondria. And loss motility of the mitochondria shows poor ATP productive ratios, resulting in a phenotype like that observed in the cells. This data suggests that functional activity of the mitochondria is associated with the microtubule stability in the cells. And microtubule stabilizer has a possibility to recovery functional activity in the microtubule instable cell like aging process. This finding can be applying to understand the mechanism of aging.Support or Funding InformationThis research was supported by the University Innovation Support Project (UISP) through the National Research Foundation (NRF) funded by MEST(Project No. 20190104)CCK analysis(A) and cell morphology(B) of NaB and Taxol treated cellsFigure 1ATP productive ratios(A) and fission form of mitochondria(B) of cellsFigure 2

Design of an in-core fission-spectrum neutron irradiation facility with pneumatic sample transfer at a research reactor

The primary objective of the work being presented is to design and optimize a fast neutron irradiation facility with pneumatic sample transfer for use in fast neutron activation analysis. The facility will be used to improve uncertainties in the yields of fission products induced by fission neutrons. Various materials and geometric designs were researched and modeled in MCNP for the filtration of thermal neutrons from a research reactor core. These models yielded the finalized design of a layered cylindrical system to be placed in the 3-EL irradiation position in the core of the TRIGA MARK-II reactor at The University of Texas at Austin. The design balances the need to maintain high total neutron flux with the careful shaping of a neutron spectrum to be as close to the Watt fission spectrum as possible. The models indicate that thermal neutron flux may be reduced by at least five orders of magnitude while only reducing the overall fast neutron flux by less than an order of magnitude. The fast:(thermal+epithermal) fission ratio should exceed 100:1 with an integrated fast flux value (defined > 0.001 MeV) of at least 7.8×1011 n cm−2 s−1.

Histopathological evaluation of crypt fission during intestinal development in neonatal mice.

Pathological evaluation of juvenile toxicity studies requires the understanding of normal tissue development at different ages. Here, we report the morphological features of the neonatal mouse intestine, focusing on crypt fission. Postnatal day (PND) 7 and 14 mice showed fewer crypts and less mature epithelial morphology compared to PND 21 and 28. Crypt fission occurred in three stages: 1) flattening of the crypt base into a skirt shape, 2) penetration of myofibroblasts into the crypt base center, and 3) complete separation of a single crypt into two daughter crypts. The ratio of crypt fission to total number of crypts was the highest at PND 14 and 7 in the jejunum and colon, respectively. Crypt fission, a key phenomenon for balance or imbalance in epithelial cell hierarchy, including stem and differentiated cells, is related to tissue injury repair and tumorigenesis. Therefore, examining crypt fission can provide valuable insights into current conditions of intestine.

Mitochondrial Network State Scales mtDNA Genetic Dynamics

Mitochondrial DNA (mtDNA) mutations cause severe congenital diseases but may also be associated with healthy aging. mtDNA is stochastically replicated and degraded, and exists within organelles which undergo dynamic fusion and fission. The role of the resulting mitochondrial networks in the time evolution of the cellular proportion of mutated mtDNA molecules (heteroplasmy), and cell-to-cell variability in heteroplasmy (heteroplasmy variance), remains incompletely understood. Heteroplasmy variance is particularly important since it modulates the number of pathological cells in a tissue. Here, we provide the first wide-reaching theoretical framework which bridges mitochondrial network and genetic states. We show that, under a range of conditions, the (genetic) rate of increase in heteroplasmy variance and de novo mutation are proportionally modulated by the (physical) fraction of unfused mitochondria, independently of the absolute fission–fusion rate. In the context of selective fusion, we show that intermediate fusion:fission ratios are optimal for the clearance of mtDNA mutants. Our findings imply that modulating network state, mitophagy rate, and copy number to slow down heteroplasmy dynamics when mean heteroplasmy is low could have therapeutic advantages for mitochondrial disease and healthy aging.

Hydrogen sulfide attenuates homocysteine-induced osteoblast dysfunction by inhibiting mitochondrial toxicity.

Homocysteine (Hcy) is detrimental to bone health in a mouse model of diet-induced hyperhomocysteinemia (HHcy). However, little is known about Hcy-mediated osteoblast dysfunction via mitochondrial oxidative damage. Hydrogen sulfide (H2 S) has potent antioxidant, anti-inflammatory, and antiapoptotic effects. In this study, we hypothesized that the H2 S mediated recovery of osteoblast dysfunction by maintaining mitochondrial biogenesis in Hcy-treated osteoblast cultures in vitro. MC3T3-E1 osteoblastic cells were exposed to Hcy treatment in the presence or absence of an H2 S donor (NaHS). Cell viability, osteogenic differentiation, reactive oxygen species (ROS) production were determined. Mitochondrial DNA copy number, adenosine triphosphate (ATP) production, and oxygen consumption were also measured. Our results demonstrated that administration of Hcy increases the intracellular Hcy level and decreases intracellular H2 S level and expression of the cystathionine β-synthase/Cystathionine γ-lyase system, thereby inhibiting osteogenic differentiation. Pretreatment with NaHS attenuated Hcy-induced mitochondrial toxicity (production of total ROS and mito-ROS, ratio of mitochondrial fission (DRP-1)/fusion (Mfn-2)) and restored ATP production and mitochondrial DNA copy numbers as well as oxygen consumption in the osteoblast as compared with the control, indicating its protective effects against Hcy-induced mitochondrial toxicity. In addition, NaHS also decreased the release of cytochrome c from the mitochondria to the cytosol, which induces cell apoptosis. Finally, flow cytometry confirmed that NaHS can rescue cells from apoptosis induced by Hcy. Our studies strongly suggest that NaHS has beneficial effects on mitochondrial toxicity, and could be developed as a potential therapeutic agent against HHcy-induced mitochondrial dysfunction in cultured osteoblasts in vitro.

PEMANFAATAN LIMBAH JAMUR TIRAM SEBAGAI PUPUK ORGANIK PADA BUDIDAYA SELADA (Lactuca sativa L.)

Oyster mushroom growing media generally in the form of sawdust. The sawdust contains high levels of cellulose, hemicellulose and lignin so that the C/N ratio is high. Mixing with manure and composting are one way to improve the quality of compost. The purpose of this study was to determine the effect of oyster mushroom waste combined with fermentation time on lettuce growth. The research method used a randomized block design with treatment namely A=oyster mushroom media waste 100% fermented 20 days, B=oyster mushroom waste 100% fermented 25 days C=75% oyster mushroom waste+25% goat manure fermented 20 days, D=75% oyster mushroom waste+25% goat manure fermented 25 days, E=50% oyster mushroom waste+50% goat manure fermented 20 days, F=50% oyster mushroom waste+50% goat manure fermented 25 days, G=25% oyster mushroom waste+75% goat manure fermented 20 days, H=25% oyster mushroom waste+75% goat manure fermented 25 days each treatment was repeated four times. Parameter observed were leaf area, number of leaves, net assimilation rate, root and wet weight ratio per plant. The results showed that a combination of compost consisting of 25% mushroom waste+75% goat manure both fermented 20 days and 25 days had a good influence on leaf area, leaf number, root fission ratio and weight of wet stover per lettuce plant. Keywords: Compost, Fermentation, Lettuce, Organic fertilizer

Measurement of 232Th(n,f) and 232Th(n,γ) reaction rates in thorium powder cylinder bombarded with D-T neutrons

ABSTRACTIn order to provide reference for the evaluation of thorium parameters for the conceptual design of fusion–fission hybrid energy reactor, a dedicated integral experiment was carried out in a thorium powder cylinder bombarded with D-T neutrons. Thorium capture and fission rates in the 0° direction to the incident D+ beam were obtained using the activation method followed by the off-line gamma-ray technique, experimental uncertainties were ∼3.1% for thorium capture rate, and were 5.5%, 8.1%, and 6.3% for thorium fission rates based on fission products 85mKr, 143Ce, and 87Kr, respectively. The thorium fission rate based on 85mKr agreed well with the simulation employing ENDF/B-VII.0 library data. The influence of the oxygen contained in the thorium oxide powder and the scattering neutrons from the experimental hall was also evaluated. MCNP simulations employing ENDF/B-Ⅶ.0, JENDL-4.0 library data agreed with experiment within uncertainties except that employing ENDF/B-Ⅶ.1 (6.0%) and CENDL-3.1 (7.9%) for thorium fission rate, while for thorium capture rate, simulation employing JENDL-4.0 agreed with experiment best. The influence of reaction channels of thorium transport medium employing different library data on the thorium reaction rates could be neglected according to the simulation. The thorium capture to fission ratio demonstrated that the fuel breeding efficiency is quite low and energy production plays a leading role under the neutron spectra in this experiment.

Abstract P222: Ablation of Tool Like Receptor-4 Mitigates Blood Pressure Response During Hyperhomocysteinemia

Background: A significant number of studies have shown a positive correlation between Hcy plasma levels and hypertension. On the other hand pathogen recognition receptor, and in particular TLR-4 is a foreign antigen sensor that plays role in innate immune system activation and has recently gained a significant attention in the field of hypertension. Mitochondrial dysfunction and mitochondria-dependent apoptosis have been shown to promote endothelial cell loss leading to endothelial dysfunction that contributes to pathogenesis of hypertension. These events induce mitochondrial dysfunction characterized by excessive mitochondrial fission and mitochondrial apoptosis contributing to vascular remodeling followed by hypertension. Objective: The objective of this study is to define the mechanisms of homocysteine effect on aortic wall that promote vascular remodeling and hypertension and explore the role of TLR-4 mutation in alleviation of homocysteine negative effects. Methods: For this study we used 5 groups of mice: C57BL/6J, C3H/HEouJ, CBS+/-; C3H/HeJ, and CBS+/-/C3H. For further analysis we used isolated aorta and collected blood. Blood pressure was recorded using noninvasive tail cuff method. Effects of hyperpolarization factor and endothelial-dependent vasodilator on aorta contractility were also performed. We checked expression of mitochondrial fusion and fission proteins, antioxidant markers and expression of collagen/elastin fragments. Results: Data showed that there were increased values of systolic and diastolic pressure in CBS+/- mice (DP: 127.06±18.24; SP: 159.59±15.84) and C3H/HeJ mice had decreased levels of in comparing to other groups (DP: 55.43±16.19; SP: 110.04±5.90). The response to hyperpolarization factor and endothelial-dependent vasodilator were blended in CBS+/- aorta, however mitigated in CBS+/-/C3H. Fusion and fission ratio (Mfn2/DRP1) were increased in C3H/HeJ mice (1.53±0.08) and mostly decreased in CBS+/- mice (0.42±0.05) compering to other groups. Conclusion: These findings indicate the prevalence of mitochondrial fission over mitochondrial fusion in HHcy may explain possible endothelial cell loss and dysfunction followed by collagen accumulation that contributes to vascular remodeling.

Solution-Phase Singlet Fission in a Structurally Well-Defined Norbornyl-Bridged Tetracene Dimer.

The photophysics of a norbornyl-bridged covalent tetracene (Tc) dimer BT1 and a monomer analogue Tc-e were studied in room-temperature nonpolar solvents. Notably in BT1, a Davydov-split band is observed in UV absorption, heralding interchromophore electronic interactions. Emission spectra indicate an acene-like vibronic progression mirroring the lowest-energy visible absorption. For BT1, this argues against excited-state excimer formation. Evidence of intramolecular singlet fission (SF) comes from a comparison of time-resolved emission decay signals collected for BT1 versus Tc-e in toluene. In BT1, the multiexcitonic (1)TT state is produced in 70 ns in 6% yield. A ratio of fission versus fusion rate constants provides an experimental measure of the SF reaction free energy at 52 meV in good agreement with previous calculations. The low SF yield corroborates our expectations that orbital symmetry effects on diabatic coupling for SF are important for dimers that cannot rely on more favorable thermodynamics.

Study of the release of the fission gases (Xe and Kr) and the fission products (Cs and I) under anoxic conditions in bicarbonate water

ABSTRACTFor safety assessment analyses of the disposal of spent nuclear fuel (SNF) in deep geological repositories it is indispensable to evaluate the contribution of fission products to the instant release fraction (IRF). During the last three years the EURATOM FP7 Collaborative Project, “Fast / Instant Release of Safety Relevant Radionuclides from Spent Nuclear Fuel (CP FIRST-Nuclides)” was carried out to get a better understanding of the IRF.Within CP FIRST-Nuclides, a leaching experiment with a cladded SNF pellet was performed in bicarbonate water (19 mM NaCl + 1 mM NaHCO3) under Ar /H2 atmosphere over 333 days. The cladded SNF pellet was obtained from a fuel rod segment which was irradiated in the Gösgen pressurized water reactor; the average burn-up of the segment was 50.4 MWd/kgUO2. In the multi-sampling experiment, gaseous and liquid samples were taken periodically. The moles of the fission gases Kr and Xe released in the gas phase and those of 129I and 137Cs released in solution were measured. Cumulative release fractions of (1.6 ± 0.2)·10-1 fission gases, (1.6 ± 0.1)·10-1129I and (3.9 ± 0.2)·10-2 137Cs, respectively, were achieved after 333 days of leaching. Accordingly the release ratio of fission gases to 129I was 1:1 and the release ratio of fission gases to 137Cs was 4:1, respectively.

Physical investigation for neutron consumption and multiplication in fusion–fission hybrid test blanket module

Inelastic scattering of high energy fusion neutrons does affect the performance of fusion blanket based on the choice of different materials. It will also affect the behavior of source neutrons in a subcritical fusion fission hybrid blanket and consequently the transmutation and tritium breeding performance. A fusion fission hybrid test blanket module (HTBM) is designed which is presumed to be tested in a large sized tokamak and plasma neutron source is similar to ITER. In this preliminary design of HTBM the neutron source and loss factors are computed for the detailed neutronic performance analysis. The neutronic analysis of hybrid blanket module is performed for five different TRU fuel types: TRU-Zr, TRU-Mo, TRU-Oxide, TRU-Carbide and TRU-Nitride. In this module design, it is aimed to burn and transmute the TRU nuclides from high-level radioactive waste of PWR spent fuel. The effect of TiC reflector on transmutation and tritium breeding performance of HTBM is also quantified. MCNPX is used for neutronic computations. Neutron spectrum, capture to fission ratio and waste transmutation ratio of each fuel type are compared to evaluate their waste transmutation performance. Tritium breeding ratio is also compared for two coolant options: Li and LiPb eutectic.

Determination of the 238U capture to total fission ratio in alternate depleted uranium/polyethylene shells with D-T neutrons

Aiming at checking the conceptual design of the subcritical blanket in the fusion–fission hybrid reactor, an integral experiment was carried out on an alternate depleted uranium/polyethylene-shell setup with D-T neutrons using activation technique. 18 depleted uranium foils were placed at 90° direction to the incident D beam, and the distribution of the 238U capture to total fission ratio was determined by measuring the 277.6keV γ ray generated by neutron capture of 238U and the 293.3keV γ ray generated by fission of 235U and 238U. The ratios were generally between 1 and 2 in the depleted uranium shells, with relative uncertainties between 3.0% and 5.5%. The ratios were calculated by the MCNP4B code employing ENDF/B-VI nuclear data library, the discrepancies between calculations and experiments were all within 6%, and the average calculation to experiment(C/E) ratio was 0.998.

Perturbations in Mitochondrial Dynamics Induced by Human Mutant PINK1 Can Be Rescued by the Mitochondrial Division Inhibitor mdivi-1

Mutations in the mitochondrial encoded protein PTEN-induced putative kinase 1 (PINK1) cause autosomal recessive Parkinson disease (PD). In mammalian cells, mutant PINK1 has been reported to promote fission or inhibit fusion in mitochondria; however, the mechanism by which this process occurs remains elusive. Using an ecdysone-inducible expression system in mammalian dopaminergic neuronal cells, we report here that human mutant PINK1 (L347P and W437X) mediates an overall fission effect by increasing the ratio of mitochondrial fission over fusion proteins, leading to excessive dysfunctional fragmented mitochondria. Knocking down endogenous Pink1 produces similar effects. In contrast, overexpressing human wild type PINK1 produces a pro-fusion effect by increasing the ratio of mitochondrial fusion/fission proteins without resulting in functionally compromised mitochondria. Parkin knockdown blocks the imbalance in fission/fusion proteins. Furthermore, overexpressing parkin and ubiquitin increases degradation of the mitochondrial fission hFis1 protein, suggesting PINK1 and parkin maintain proper mitochondrial function and integrity via the fission/fusion machinery. Through genetic manipulations and treatment with the small molecule mitochondrial division inhibitor (mdivi-1), which inhibits DLP1/Drp1, both structural and functional mitochondrial defects induced by mutant PINK1 were attenuated, highlighting a potential novel therapeutic avenue for Parkinson disease.

The systematic study of spontaneous fission versus alpha decay of superheavy nuclei

The competition between the alpha decay and spontaneous fission half-lives of even–even elements with Z = 100–122 is studied using the Coulomb and proximity potential model and the phenomenological formula for spontaneous fission. The isotopes situated within the spontaneous fission half-life parabola will have alpha decay as the dominant mode of decay. We have studied the Seaborg plots connecting the spontaneous fission half-lives with the fissionability parameter (Z2/A) in the superheavy region for isotopes with Z = 100–138. The role of relative neutron excess in spontaneous fission half-lives is also studied. The isotopes in the first quadrant of the plot for the ratio of spontaneous fission to alpha decay half-lives against relative neutron excess will survive fission and can be synthesized and detected through alpha decay. Our computed alpha decay half-lives for all isotopes agree with the values calculated by the Viola–Seaborg empirical formula and with the experimental data.

Performance of the gas turbine-modular helium reactor fuelled with different types of fertile TRISO particles

Preliminary studies have been performed on operation of the gas turbine-modular helium reactor (GT-MHR) with a thorium based fuel. The major options for a thorium fuel are a mixture with light water reactors spent fuel, mixture with military plutonium or with with fissile isotopes of uranium. Consequently, we assumed three models of the fuel containing a mixture of thorium with 239Pu, 233U or 235U in TRISO particles with a different kernel radius keeping constant the packing fraction at the level of 37.5%, which corresponds to the current compacting process limit. In order to allow thorium to act as a breeder of fissile uranium and ensure conditions for a self-sustaining fission chain, the fresh fuel must contain a certain quantity of fissile isotope at beginning of life; we refer to the initial fissile nuclide as triggering isotope. The small capture cross-section of 232Th in the thermal neutron energy range, compared to the fission one of the common fissile isotopes ( 239Pu, 233U and 235U), requires a quantity of thorium 25–30 times greater than that one of the triggering isotope in order to equilibrate the reaction rates. At the same time, the amount of the triggering isotope must be enough to set the criticality condition of the reactor. These two conditions must be simultaneously satisfied. The necessity of a large mass of fuel forces to utilize TRISO particles with a large radius of the kernel, 300 μm. Moreover, in order to improve the neutron economics, a fuel cycle based on thorium requires a low capture to fission ratio of the triggering isotope. Amid the common fissile isotopes, 233U, 235U and 239Pu, we have found that only the uranium nuclides have shown to have the suitable neutronic features to enable the GT-MHR to work on a fuel based on thorium.

Predation Effects on the Evolution of Life‐History Traits in a Clonal Oligochaete

Although size at maturity and size and number of offspring are life-history traits widely studied in sexual and parthenogenetic reproduction, there is no such research on animals reproducing asexually without the involvement of gametes. Here we present an individual-based model in combination with experiments to study the clonal growth of Stylaria lacustris, an oligochaete reproducing through fission. We studied the effect of individual size at fission and fission ratio on clone fitness. Our results show that in benign environments without predators, fitness is higher when small worms produce small offspring. Then we included size-specific sublethal predation and found that the fitness of the clone is maximized when parental worms start fission at a large size and produce large descendants intercalated in the middle of the parental worm's body. These results agree with empirical findings. Furthermore, the results of our own laboratory experiment revealed that when S. lacustris is exposed to chemical alarm signals from injured conspecifics, it alters its life history in the same direction as predicted by the model. Our findings suggest that the effect of size-specific sublethal predation is similar to the effect of size-specific lethal predation because both modes of predation result in size-dependent prey mortality.

Temperature of low-energy ternary fission from the dependence of particle yields on the mass of the fissioning system

In thermal neutron-induced and spontaneous fission the addition of two neutrons to a neutron-even system produces only minor changes to the shape, kinetic energy, and temperature of the scission configuration. If these changes are assumed negligible and if ternary fission is associated with a statistical process then the ratio of ternary fission yields for systems differing by two atomic mass units can be used to infer a nuclear temperature. The yields of hydrogen, helium, lithium, and beryllium isotopes ejected perpendicular to the direction of the main fragments from $^{233,235}\mathrm{U}({n}_{\mathrm{th}},f)$, $^{239,241}\mathrm{Pu}({n}_{\mathrm{th}},f)$, and $^{250,252}\mathrm{Cf}$ spontaneous fission give a nuclear temperature $T=1.24\ifmmode\pm\else\textpm\fi{}0.10\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The yield of polar $\ensuremath{\alpha}$ particles from $^{233,235}\mathrm{U}({n}_{\mathrm{th}},f)$ give $T=1.13\ifmmode\pm\else\textpm\fi{}0.24\phantom{\rule{0.3em}{0ex}}\text{MeV}$. These results are in agreement with other inferred low-energy ternary fission temperatures and support the idea that both equatorial and polar ternary fission involve a statistical process where the ejected particles are in equilibrium with a heat bath with a temperature slightly hotter than 1 MeV.