Energetic Fragments Research Articles

Density functional theory (DFT) study on the structures and energy properties of high energy density materials based on polynitroazofurazan derivatives

In this study, inspired by the structures of the heat resistant explosives 5,5’-bis(2,4,6-trinitrophenyl)-2,2′-bi(1,3,4-oxadiazole) and 2,6-bis(picrylamino)-3,5-dinitro-pyridine, five high energy and low sensitivity energetic materials have been designed by combining the energetic fragments with the high energy azofurazan skeleton, and structure - property relationships have been investigated by means of density function theory. All compounds have excellent explosive properties (Dv: 7946–8341 m/s; P: 27.6–30.9 GPa) and high positive heats of formation (816.85–940.28 kJ/mol). Among them, compounds 3 and 4 have the best explosive properties (3: Dv: 8318 m/s P:30.7 GPa; 4: Dv: 8341 m/s P: 30.9 GPa), which are comparable to 1,3,5-trinitrohexahydro-1,3,5-triazine. The h50 values indicate that all compounds have good impact sensitivity, comparable to 1,3,5,7-tetranitro-1,3,5,7-tetrazocane and 1,3,5-trinitrohexahydro-1,3,5-triazine and superior to hexanitrohexaazaisowurtzitane. In addition, bond dissociation energies, frontier molecular orbitals, and weak interaction, etc. are calculated to further investigate the relationship between structures and properties. The calculated results show that these compounds are expected to be the next generation of high energy density materials with an excellent balance of energetic properties and stability.

Sensitive detection and imaging of H2O density through Rydberg resonant femtosecond laser induced photofragmentation fluorescence.

A femtosecond laser induced photofragmentation fluorescence (fs-LIPF) scheme for the sensitive detection and imaging of water vapor is presented. Two photons of 244.3nm excite water to the D̃ state and produce hydroxyl radicals in the fluorescing à state. Two more photons promote electrons from the D̃ state to a neutral Rydberg state of the (1b2)-1 ionic core through a 2 + 2 doubly resonant process. The resulting high-lying Rydberg state undergoes neutral dissociation, and the energetic hydrogen fragments are detected from their Balmer series fluorescence. These channels (in the low-pressure limit) have detection sensitivities around 1012 molecules per cubic centimeters, orders of magnitude more sensitive than laser-induced fluorescence based approaches, allowing for sensitive non-invasive detection and imaging of water density for many important processes.

The role of xenon/krypton adsorption on the growth of intra-granular bubbles in irradiated UO2

Under transient conditions, rapid fuel swelling in UO2 can occur through fission gas and vacancy capture by intra-granular bubbles. These swellings can lead to significant cladding deformations and clad failure. To understand the mechanisms of intra-granular swelling a number of key experiments have been conducted by the UK in conjunction with the Halden Reactor. Post-irradiation annealing enables the study of the thermal behaviour of the intra-granular bubbles in the absence of complicating processes such as irradiation-induced bubble destruction and fission gas resolution. Bubble-like features are frequently observed in straight lines and it has always been assumed that these were nucleated in the wake of energetic fission fragments and served as nuclei for bubble growth. However, most of these bubbles do not grow significantly and viable intra-granular bubbles are nucleated at much lower densities. At the temperature and pressure that these form, the xenon and krypton are above their critical points and the elements are supercritical fluids. However, bubble growth occurs at temperatures and pressures much greater than the critical points and the gases may be treated with simple equations of state such as those by Clausius or Van der Waals. Of greater importance is the fact that the large Van der Waals forces in these atoms generated by fluctuations in the electron dispositions lead to extensive adsorption on the inner surfaces of the bubbles and vacancy capture by the bubbles can lead to the diffusive loss of fission gas atoms resulting in bubble growth at slight over-pressure conditions. A diffusion model based on Langmuir Adsorption has been developed and shown to be consistent with the out-of-pile annealing studies.

Mechanical behavior and optimization of constitutive prediction model for Epoxy/Al energetic composite materials considering temperature and strain rate effects

Epoxy/Al as a functional structural energetic composite material that can be used as an adhesive, energetic fragments and warhead shells due to its high energy density, low density, and high strength. It can release a large amount of chemical energy (about 21.36 kJ/g) through chemical reactions when subjected to high-speed impact and thermal stimulation. Whether used as a matrix or auxiliary component, it has enormous development potential. Therefore, it is particularly important to study the mechanical properties of Epoxy/Al energetic composite materials under different temperature environments and strain rates of loading. This article describes the preparation of Epoxy/Al specimens with a mass percentage of 70%–30% using vacuum curing after 24 h under 0.8 Bar and 50 °C. The mechanical properties of Epoxy/Al specimens under different loading conditions were characterized using a high and low temperature universal testing machine and a separate Hopkinson experimental system. The modulus prediction method of binary composite materials was improved by combining SEM (scanning electron microscopy) and microstructure, and an adaptive constitutive model was developed combined with the K Srinivas model and neural network model based on the Sherwood Frost empirical constitutive relationship. The results show that Epoxy/Al energetic composite material has a significant temperature effect. When the temperature exceeds 100 °C, Epoxy/Al energetic composite material will be a significant physical and chemical property transition (the specimen exhibits viscous fluid characteristics and gradually begins to slowly decompose). As the temperature decreases, the specimen gradually exhibits a certain degree of brittleness and strength is improved. Due to the deformation, displacement, and interfacial debonding of internal particles during the loading process, Epoxy/Al materials exhibit excellent impact energy absorption effects, with energy absorption reaching 15.30 MJ/m3 at room temperature, and unit mass cost much lower than popular CFRP (carbon fiber-reinforced polymer) materials (CFRP energy absorption cost is 0.268 J/g/£, while Epoxy/Al materials do not exceed 0.013 J/g/£). During the dynamic loading process, Epoxy/Al energetic composite materials exhibit a phenomenon of structural reconstruction and enhancement throughout the entire loading process. The maximum strength at room temperature can reach 240.70 MPa, which is superior to all existing energetic materials of the same type. By introducing interface effects and quantifying them in the Halpin Tsai model, the existing prediction method for the Young's modulus of binary particle added composite materials has been effectively improved, reducing the prediction error of the Young's modulus of Epoxy/Al energetic composite materials from 14.2% to 2.4%. The numerical simulation results indicate that the newly developed constitutive model has high accuracy and can better reflect the mechanical properties of Epoxy/Al materials. The development method of this constitutive model has a positive contribution to the development of composite materials.

Experimental study on damage aftereffect of several types of metallic energetic fragments

Metallic energetic fragments are the most widely used and technologically mature damage fragments at present. In this study, four types of typical tungsten/zirconium (W/Zr) energetic fragments are examined by static explosion test, and the penetration, hole enlargement, and ignition performance and characteristics of different fragment materials are investigated. The results show that all the four W/Zr energetic fragments have good anti-detonation and penetration capabilities, which can effectively penetrate 6 mm thick Q235 steel plate, aluminum spacer plate and fuel tank behind the target at impact velocity of 1050 m/s. 1#, 2# and 4# energetic fragments exhibit significant behind-target hole enlargement effect, and the enlarged area of holes in the aftereffect aluminum plate behind the steel plate with a spacing of 10 cm is 6~8 times the cross-sectional area of the original fragment, and the enlarged hole area of the fuel tank (outlet) behind the aluminum plate is 12~14 times the cross-sectional area of the original fragment. 3# fragments has weaker behind-target hole enlargement effect. Low-density 2# and 4# fragments can ignite the aviation kerosene tank behind the target, and 4# fragments show the best ignition effect. There is an internal consistency between hole enlargement capability on the aftereffect target of energetic fragments and the behind-target ignition capability. Without sacrificing the anti-detonation and penetration performance, low-density energetic fragments can be preferentially selected to ensure the behind-target damage effect.

Characterization of a platform for the gas transport, collection, and identification of fission products in the high-intensity laser environment

Recent progress in the production of laser accelerated high flux proton beams opens new possibilities for the study of fission in unique environments. To this end, we are currently pursuing the development of a platform for the swift gas transport, collection, and identification of fission products. Fission is induced in targets fixed inside a sealed chamber through which a carrier gas flows, transporting fission products to a carbon filter for collection and online spectroscopy. This has been recently demonstrated using target normal sheath accelerated protons at the PHELIX laser facility. There were large discrepancies between measured rates and those expected based on established fission yields and measured beam parameters. These discrepancies prompted a large number of tests at the Idaho Accelerator Center (IAC), where fission in uranium is induced by bremsstrahlung photons generated by 21 MeV electrons from a linear electron accelerator. The results are compared to a series of models that account for the slowing of energetic fission fragments in the carrier gas and the fluid dynamics of the gas flow that transports fission products to the collection filter. Characterization of the apparatus reveals a few mechanisms that together account for a portion of the previously observed discrepancies at the PHELIX laser facility. However, additional research is necessary before high-accuracy experiments can be performed with the apparatus. Work performed under the auspices of the U.S. Department of Energy by LLNL under contract DE-AC52-07NA27344.

A case study for heat and mass transfer of viscous fluid flow in double layer due to ciliated channel

The present study is a measurement of the thermal and mass transfer of a two-layered flow of viscous fluid induced by cilia motion under the effect of buoyancy forces through a channel. Cilia are mostly of two classes: motile and non-motile cilia for locomotion and sensory processing. Cilia tissue cells are epithelia lining the lungs that sweep away liquids or solids, and organisms that have cilia are protozoans that use them for movements are the examples. The ciliary apparatus is related to cell cycle movement and proliferation, and cilia display an energetic fragment in human and animal development and in ordinary life. The fluid is considered to be incompressible, and layers of fluid do not mix with each other. The fluid flow for mass and thermal transfer is modelled in wave and fixed frame. Solutions for temperature, velocity of fluid, and concentration profile are obtained using a well-known method, namely the Homotopy Perturbation Method (HPM), by the computation software "MATHEMATICA". The behavior of emerging parameters is shown graphically in the results section. Graphical results can be analyzed for the temperature and velocity profile, which are extreme in the inner layer for both fluid and concentration distribution and are highest at the external layers of fluid. It is the first study not examined in the literature.

Study on the Ignition Mechanism of Inert Fuel Tank Subjected to High-Velocity Impact of Fragments.

Nowadays, aircraft fuel tanks are protected by measures such as inerting, fire and explosion suppression, which significantly improve their ability to mitigate mechanical damage and prevent fire in the case of an accidental attack. In this study, an equivalent inert fuel tank with fire and explosion suppression was designed according to the vulnerabilities of a typical fighter. Then, a ballistic gun, a 37 mm gun and a two-stage light-gas gun were used to propel different fragments in tank damage experiments at different speeds (1400 m/s–2600 m/s). Experimental results show that the disassembly of a fuel tank is a prerequisite for igniting fuel. When the fragments hit the gas phase of the tank, the fuel tank was not disassembled and the fuel was not ignited. The calculation results show that the internal oxygen concentration was always lower than the limiting oxygen concentration (12%) before the fuel tank was disassembled. In addition, the minimum ignition speeds of inerted fragments with different masses as predicted by the ignition criterion when hitting the liquid fuel are consistent with the test results. This shows that increasing the mass of inert fragments will increase the minimum ignition speed and reduce the probability of ignition of the fuel. However, the implosion effect of the energetic fragments released about 3 times the chemical energy of its own kinetic energy, and the high-temperature and high-pressure products were very beneficial to the disintegration and ignition of the fuel tank compared to inert fragments.

Super-short fission mode in fermium isotopes

The so-called super-short fission mode, in which a nucleus divides nearly symmetrically into two unusually energetic fragments, competes favorably with the standard asymmetric fission mode for spontaneous fission of a limited number of nuclei near $^{264}\mathrm{Fm}$ but it quickly fades away at finite excitations. We investigate the energy-dependent competition between those two fission modes for even fermium isotopes from $^{254}\mathrm{Fm}$ to $^{268}\mathrm{Fm}$, using the Metropolis method to simulate the strongly damped fission dynamics being driven by shape- and energy-dependent level densities. The origin of the super-short mode is discussed and its effects on the fragment mass distribution, the total fragment kinetic energy, and the neutron multiplicity are calculated. Generally good agreement with the available data is obtained.

Effect of increasing Ti content on the phase, interface, dynamic mechanical properties and ballistic performance of W–Ti–Zr alloys

W2Zr intermetallic is an important reason for the brittleness of W–Zr binary system. When W–Zr alloys are used as the energetic fragment, the integrity of a projectile cannot be maintained under the explosion even propellant loading process, resulting in severe fracture of the projectile. Moreover, due to the strong atomic bonding in W2Zr intermetallic, the oxidation reactivity of the Zr atoms with oxygen in the air is significantly suppressed, limiting the effective energy release of W–Zr fragment under high-speed impacting process. In this study, based on the thermodynamic analysis, 30W-xTi-(70-x)Zr (wt.%) alloys were designed and prepared by powder metallurgy. It was found that the formation and stabilization temperature of W2Zr phase can be reduced by increasing the Ti content. The hard W-rich phase has changed from the coarse W2Zr particle to fine W2Zr precipitate and finally to the WTix solid solution with the increase of Ti content. Meanwhile, a semi-coherent interface between fine W2Zr precipitate and α matrix and even coherent interface between WTix and α matrix were formed, by which the intergranular fracture ratio between W-rich phases and α matrix was significantly decreased in the W–Ti–Zr alloys. Consequently, higher dynamic compressive strength and ductility of the W–Ti–Zr alloys were obtained by increasing the Ti content. The selected W–Ti–Zr alloys with high strength and proper failure strain exhibited good penetration and energy-releasing behaviors when they were used as reactive bullet launching at a velocity of about 1250 m/s. The relationship among the dynamic compressive strength, ductility and ballistic performance of the W–Ti–Zr reactive structural alloys was also discussed in detail.

Biological Impact of Target Fragments on Proton Treatment Plans: An Analysis Based on the Current Cross-Section Data and a Full Mixed Field Approach.

Simple SummaryProton therapy is now an established external radiotherapy modality for cancer treatment. Clinical routine currently neglects the radiobiological impact of nuclear target fragments even if experimental evidences show a significant enhancement in cell-killing effect due to secondary particles. This paper quantifies the contribution of proton target fragments of different charge in different irradiation scenarios and compares the computationally predicted corrections to the overall biological dose with experimental data.Clinical routine in proton therapy currently neglects the radiobiological impact of nuclear target fragments generated by proton beams. This is partially due to the difficult characterization of the irradiation field. The detection of low energetic fragments, secondary protons and fragments, is in fact challenging due to their very short range. However, considering their low residual energy and therefore high LET, the possible contribution of such heavy particles to the overall biological effect could be not negligible. In this context, we performed a systematic analysis aimed at an explicit assessment of the RBE (relative biological effectiveness, i.e., the ratio of photon to proton physical dose needed to achieve the same biological effect) contribution of target fragments in the biological dose calculations of proton fields. The TOPAS Monte Carlo code has been used to characterize the radiation field, i.e., for the scoring of primary protons and fragments in an exemplary water target. TRiP98, in combination with LEM IV RBE tables, was then employed to evaluate the RBE with a mixed field approach accounting for fragments’ contributions. The results were compared with that obtained by considering only primary protons for the pristine beam and spread out Bragg peak (SOBP) irradiations, in order to estimate the relative weight of target fragments to the overall RBE. A sensitivity analysis of the secondary particles production cross-sections to the biological dose has been also carried out in this study. Finally, our modeling approach was applied to the analysis of a selection of cell survival and RBE data extracted from published in vitro studies. Our results indicate that, for high energy proton beams, the main contribution to the biological effect due to the secondary particles can be attributed to secondary protons, while the contribution of heavier fragments is mainly due to helium. The impact of target fragments on the biological dose is maximized in the entrance channels and for small values. When applied to the description of survival data, model predictions including all fragments allowed better agreement to experimental data at high energies, while a minor effect was observed in the peak region. An improved description was also obtained when including the fragments’ contribution to describe RBE data. Overall, this analysis indicates that a minor contribution can be expected to the overall RBE resulting from target fragments. However, considering the fragmentation effects can improve the agreement with experimental data for high energy proton beams.

Construction of Layered High-Energy Materials via Directional Hydrogen Bonding

Energetic substances with layered crystal packing have been identified as the most promising next-generation high-energy materials (HEMs) due to their excellent insensitivity. The challenge, however, is how to design layered HEMs. In this study, a novel strategy called “acceptor–donor separation” was proposed to control the layer-by-layer stacking of energetic molecules through directional hydrogen boding: that is, a hydrogen bond donor and acceptor are located in different energetic segments and at least one of them has a conjugated planar structure, which will enable the energetic fragments to be infinitely extended in a two-dimensional plane to form a target layered structure. The experimental results showed that three exemplary substances designed by using this strategy possess the expected layered structures, which have been confirmed by single-crystal X-ray diffraction, demonstrating the robustness of this strategy. Moreover, the three as-synthesized HEMs all exhibit excellent insensitivity (impact sensitivity IS > 40 J; friction sensitivity FS > 360 N), affording safety far beyond those of the most powerful HEMs in use today. Especially, the hydroxylammonium energetic salts possess good detonation performance (detonation velocity D = 8924 m s–1; detonation pressure P = 36.9 GPa) comparable to that of 1,3,5-trinitro-1,3,5-triazine (RDX), one of the most powerful high explosives in use today.

On the Use of Chromium Coating for Inner-Side Fuel Cladding Protection: Thickness Identification Based on Fission Fragments Implantation and Damage Profile

Inner-side coatings have been proposed as a complementary solution within the accident tolerant fuel (ATF) framework, to provide enhanced protection for the nuclear fuel cladding. Unlike external surface, the degradation of irradiated internal cladding surface has not been studied extensively. Fission fragments produced during the fission of nuclear fuel is one of the key players in this degradation. This study aimed to estimate the minimum thickness of the thin chromium film, required to protect the inner side of the nuclear fuel cladding. The approach used is based on a set of calculations, of Ion ranges and damage profiles, for a group fission fragments, using the TRIM code. The calculation results were verified by comparison with the experimental data associated with the phenomena of the inner cladding degradation of thermo-releasing elements. The recommended minimum thickness for such a film was found to be 9 microns. Calculations also showed that chromium metal has a greater stopping power compared to the zirconium-based alloy E110, which indicates an increased ability of chromium to withstand exposure to energetic fission fragments during reactor operation.

Dissociation dynamics of multiply charged CH3I in moderately intense laser fields

We report on the fragmentation of multiply charged ${\mathrm{CH}}_{3}\mathrm{I}$ ions through dissociative ionization and Coulomb explosion induced by moderately intense (${10}^{12}--{10}^{13} \mathrm{W}/{\mathrm{cm}}^{2}$) ultrashort laser fields. Velocity map imaging of the fragment ions as a function of pulse duration, ranging from 25 fs to 1.5 ps, leads to kinetic energies, angular distributions, and the relative ion yield in different channels of these fragments. We propose possible pathways for the fragmentation channels based on the kinetic energies and theoretical potential energy curves. For the energetic fragments, we observe an enhanced yield with increasing pulse duration. A simple one-dimensional classical model of wave-packet propagation over the proposed intermediate state potential energy curve is used to estimate the ionization probability as a function of pulse duration. Our results suggest that a delayed enhanced ionization is a consequence of rearrangement of the energies of the molecular orbitals following bond stretching. The resultant energy upshift of the inner orbitals at larger internuclear separation gives rise to resonant multiorbital coupling at a critical distance, which enables enhanced ionization for longer pulses.

Electron-impact ionization and ionic fragmentation of O2from threshold to 120 eV energy range

We study the electron-impact induced ionization of O2from threshold to 120 eV using the electron spectroscopy method. Our approach is simple in concept and embodies the ion source with a collision chamber and a mass spectrometer with a quadruple filter as a selector for the product ions. The combination of these two devices makes it possible to unequivocally collect all energetic fragment ions formed in ionization and dissociative processes and to detect them with known efficiency. The ion source allows varying and tuning the electron-impact ionization energy and the target-gas pressure. We demonstrate that for obtaining reliable results of cross-sections for inelastic processes and determining mechanisms for the formation of O[Formula: see text] ions, it is crucial to control the electron-impact energy for production of ion and the pressure in the ion source. A comparison of our results with other experimental and theoretical data shows good agreement and proves the validity of our approach.

Observing pre-edgeK-shell resonances in Kr, Xe, andXeF2

The $1s\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}np$ Rydberg transitions below the $1s$ ionization thresholds of Kr and Xe are obscured in x-ray absorption spectra due to core-hole lifetime broadening. However, the $np$ spectator electrons associated with those resonances can affect the core-hole decay spectra. We report on ion charge-state distributions of Kr and Xe measured in coincidence with ${KL}_{2,3}$ ($K{\ensuremath{\alpha}}_{1,2}$), ${KM}_{2,3}$ ($K{\ensuremath{\beta}}_{1,3}$), and ${\mathrm{KN}}_{2,3}$ ($K{\ensuremath{\beta}}_{2}$) x-ray fluorescence as the incident x-ray energy is scanned through pre-edge resonances and ionization thresholds. The coincidence measurements select vacancy cascades that begin with a radiative transition that transfers $1s$ holes to the $2p$, $3p$, and $4p$ shells followed by emission of Auger electrons. We observe shifts of ion yields from higher to lower charge states that we attribute to $np$ spectator electrons. For the special case of ${\mathrm{Kr}}^{1+}$ that is produced in coincidence with $K{\ensuremath{\beta}}_{2}$ x rays, the ion yield decreases in the pre-edge region. This is attributed to production of neutral, metastable Kr $4{p}^{\ensuremath{-}1}np$ states that reduce the ${\mathrm{Kr}}^{1+}$ yield. Model fits to the x-ray absorption spectra are presented to show the lifetime broadened pre-edge resonances and ionization thresholds. High-level relativistic coupled-cluster calculations that treat relativistic, electron correlation, and wave function relaxation effects on the same footing obtain agreement with the experimental $1s$ ionization energies of Kr and Xe to $<2$ eV. The Xe $K$-edge x-ray absorption spectrum and ion charge-state distributions of ${\mathrm{XeF}}_{2}$ were also recorded. Excitation of the $7{\ensuremath{\sigma}}_{u}$ lowest unoccupied molecular orbital (LUMO) in ${\mathrm{XeF}}_{2}$ is observed in the pre-edge region. Our ab initio calculations find that the $6{p}_{z}$ Rydberg state is strongly perturbed by the presence of the $7{\ensuremath{\sigma}}_{u}$ LUMO. A fit to the measured LUMO, $6{p}_{x}$, $6{p}_{y}$, $6{p}_{z}$ Rydberg states, and ionization threshold is guided by the relativistic coupled-cluster calculations. The F ligands modify the valence electron charge distribution and result in a $\ensuremath{\sim}2.3$ eV chemical shift of the Xe $1s$ ionization energy relative to atomic Xe. Xe $1{s}^{\ensuremath{-}1}$ core-hole decay in ${\mathrm{XeF}}_{2}$ results in ionization of the F ligands and energetic fragmentation into atomic ions. Ion charge-state spectra of ${\mathrm{XeF}}_{2}$ were recorded in coincidence with x-ray fluorescence for excitation on the LUMO resonance and above the Xe $1s$ ionization threshold. For the ion time of flight spectra recorded on the LUMO resonance, the ${\mathrm{F}}^{q+}$ ($q=1$--4) peaks are split into two peaks along the linear polarization direction of the incident x-ray beam. This effect is attributed to spatial alignment of ${\mathrm{XeF}}_{2}$ molecules by resonant x-ray absorption, and the peak splittings are used to measure the F ion fragmentation energies following $K{\ensuremath{\alpha}}_{1,2}$, $K{\ensuremath{\beta}}_{1,3}$, and $K{\ensuremath{\beta}}_{2}$ x-ray fluorescence. We observe variations of the F ion charge state yields and fragmentation energies for the three fluorescence pathways that leave the molecule in different outer-shell hole states.

2]Rotaxanes Bearing a Tetralactam Macrocycle: The Role of a Trifurcated Hydrogen Bond in the Crystalline State

This study investigated the proper classification and quantification of intercomponent trifurcated hydrogen bonds, in the crystalline state, of rotaxanes bearing a tetralactam Leigh‐type macrocycle. Quantum mechanical calculations were carried out to obtain the interaction paths and their stabilization energies. In general, the use and necessity of fragmentation in types of interaction have been reported in the literature, although they are commonly performed only using a geometric approach. This results in N–H···O interactions that are indicated as the main interactions between components, neglecting other possible interactions. The use of energetic fragmentation was demonstrated here under an appropriate demarcation considering all interactions and showing the existence and role of the C–H···O interaction. The C–H···O interactions showed similar energy to N–H···O interactions with average values around –4.75 kcal mol–1and –4.60 kcal mol–1, respectively. This revealed that the three hydrogen bonds are part of a cooperative set of interactions with a similar contribution. The trifurcated hydrogen bonds presented high contribution in the total intercomponent stabilization energy of the rotaxanes, with an average value of 51 % in the studied series.

Are small carnivores urban avoiders or adapters: Can they be used as indicators of well-planned green areas?

Terrestrial mammalian carnivores are generally sensitive to urbanization. Yet, some mesocarnivores have adapted to the urban and suburban environment. The response of small carnivores to urbanization is poorly studied, partly due to methodological difficulties. We assessed the impact of urbanization on a representative of small carnivores – the least weasel Mustela nivalis. Data from 254 trapping sessions of monitoring small mammals (27 810 trap-days) conducted in different urbanized and non-urbanized habitats (Poland, Central Europe) were used and analysed in a logistic regression model. The probability of occurrence of weasels was tested in relation to the land cover type, abundance of rodents (weasel’s food base), proportion of a built-up area (on the 500 m radius buffer) and trapping effort. The weasel avoided urban areas and if the percentage of a built-up area was higher than 32% the probability of occurrence of the weasel was low (P < 0.5). Within urbanized areas, least weasel were only detected on the outskirts of a city or in the valleys of large rivers. Conversely, habitat type did not predict the presence of least weasel in non-urbanized areas. The possible reasons for the lack of the weasel in urban green areas are narrow food specialization (mainly rodents as prey; no use of anthropogenic food sources), high energetic demands, and fragmentation and isolation of green areas. Despite the high ecological plasticity of this species, the strong negative response of the least weasel to urbanization causes that their occurrence can be an indicator of well-planned urban greenery. The occurrence of the least weasel indicates both the functional connectivity of green areas in the city and the abundance and availability of the prey base – ground-dwelling animals from lower trophic groups.

Azo1,3,4-oxadiazole as a Novel Building Block to Design High-Performance Energetic Materials

In this study, the azo1,3,4-oxadiazole energetic fragment was first introduced into the energetic materials using a simple synthetic strategy, yielding two symmetrical covalent compounds 4 and 5. All new compounds (3–5) were well-characterized by IR spectroscopy, NMR spectroscopy, thermal analysis, and single-crystal X-ray diffraction analysis. As supported by differenctial scanning calorimetry data, compounds 4 and 5 possess excellent decomposition temperatures as high as 248 and 278 °C, respectively. To the best of our knowledge, 278 °C ranks highest in all 1,3,4-oxadiazole-based energetic compounds. Their energetic performances were evaluated with EXPLO5. Both 4 and 5 show good detonation velocities (D) of 8409 and 8800 m s–1 and detonation pressures (P) of 29.3 and 35.1 GPa, comparable to RDX (D: 8795 m s–1, P: 34.9 GPa). Furthermore, on the basis of the single-crystal data, quantum-chemical calculations were employed to better understand their intrinsic structure–property relationship. All these posi...

Review of Neutron Diagnostics Based on Fission Reactions Induced by Fusion Neutrons

Neutrons are an exceptional diagnostic signature in magnetic fusion experiments with high temperature plasma. A part of neutron detection methods relies on detecting nuclear reactions products, initiated by neutrons. Among different possibilities, the neutron-induced fission reactions can be used. These methods use the specific properties of the radioactive decay phenomena induced by neutrons of heavy elements like uranium or thorium. The neutron-induced fission reactions produce energetic fission fragments that can be detected in a special type of ionization chambers that has one of electrode covered with fissionable material. A fission reaction may be also adapted to neutron detection by activation method. A dedicated target-sample made from fissionable isotope (like 235U, 238U, 232Th), irradiated by neutrons, is the source of prompt and delayed neutrons. The decay curve of delayed neutrons can be registered almost immediately after irradiation by fusion neutrons, with a delay resulting exclusively from the time of transport of the samples to the measuring set-up. The yield of a fusion neutron source can be calculated from that measurement. Fission phenomena and fissionable materials are applicable in plasma neutron diagnostics. The lecture gives the introduction to the nuclear fission process and the particular attention is done to the phenomenon and physics of delayed neutrons which are generated during the fission reaction. Examples of delayed neutrons activation set-up and fission chambers dedicated for tokamaks are presented.