Littérature scientifique sur le sujet « Super-Heavy elements (SHE) »

A new detector system dedicated for very/super heavy elements (VHE/SHE) detection that decay by spontaneous fission is presented. Such a decay mode of nuclei can be found e.g. in the region of Z ≈100 (Fermium). Future experiments realized in the frame of French-Polish collaboration at the cyclotrons in GANIL and in the Heavy Ion Laboratory (HIL), University of Warsaw, is described. The results of test measurements made in the HIL for reactions 20 Ne (8 A . MeV )+120 Sn , 179 Au are presented.

Recent experiments performed at GANIL with a crystal blocking technique have shown direct evidences of long fission times in the Super-Heavy Elements (SHE) region. Aimed to localize the SHE island of stability, can these experiments give access to the fission barrier and then to the shell-correction energy? In this paper, we calculate the fission time of heavy elements by using a new code, KEWPIE2, devoted to the study of the SHE. We also investigate the effect of potential structure beyond the saddle on the fission time.

We present a large scale survey of life-times for spontaneous fission in the regime of super-heavy elements (SHE), i.e. nuclei with Z =104-122. This is done on the basis of the Skyrme-Hartree-Fock model. The axially symmetric fission path is computed using a quadrupole constraint. Self-consistent cranking is used for the collective masses and associated quantum corrections. The actual tunneling probability is estimated by the WKB approximation. Three typical Skyrme forces are used to explore the sensitivity of the results. Benchmarks in the regime Z =104-108 show an acceptable agreement. The general systematics reflects nicely the islands of shell stabilization and the crossover from α-decay to fission for the decay chains from the region of Z / N =118/176.

Abstract Dubna Gas-Filled Recoil Separator (DGFRS-2) is a new facility at the Super Heavy Element Factory which allows us to study the properties of superheavy elements (SHEs) formed in complete fusion reactions in the femtobarn cross-section range. High dispersion and complex magnetic configuration make it difficult to tune the separator and find the optimal current values in the magnetic elements. This work presents a simulation model of the DGFRS-2 based on a GEANT4 toolkit. The main methods of trajectory simulations of heavy ions in gaseous media are discussed and several new processes are implemented in GEANT4. Calculation results agreed well with the data produced in test experiments which allows us to use this model for transmission determination and tuning of the separator in experiments aimed at SHE investigations.

One of the frontiers of today’s nuclear physics research is the synthesis of Super Heavy Elements (SHE). Fusion-fission dynamics, namely the competition between quasi fission and fusion is one of the key challenges to optimize the SHE. To have an insight into the dynamics, one requires the study of fission fragment mass and angular distribution near barrier energies for heavy-ion induced fission reactions. Recent successful installation of linear accelerators in India offers a unique opportunity to study the dynamics of nuclear reactions and formation process of SHE. For the effective utilization of these current, as well as upcoming facilities, development of novel detectors to study reaction dynamics, formation process of SHE with heavier projectiles and higher beam energies is needed. Gaseous detectors have undergone a rapid improvement in terms of spatial, temporal and energy resolution, rate capability, radiation hardness, ion feedback etc., ushering in a new genre of micro-structured devices based on semi-conductor technology, commonly known as Micro-Pattern Gaseous Detectors (MPGDs). Although many of the MPGD structures were primarily developed for high-rate tracking of charged particles in high energy physics experiments, stability of operation, simplicity of construction and relatively low cost make these detectors suitable for other applications, such as low-energy nuclear physics experiments. The present activities encompass a detailed evaluation of the operational conditions of Micromesh-Multi Wire and THGEM-Multi Wire hybrid detector operated in low-pressure isobutane gas with a view to optimizing their use in the detection of charged particles and fission fragments.

To optimize the exploration of Super Heavy Elements (SHE), the key challenge is to understand the dynamics of the fusion-fission through the measurements of mass and angular distribution of the fission fragments. For the detection of fission fragments, position sensitive Multi-Wire Proportional Counters are generally used due to their high gain, good temporal and position resolution. However, these detectors use fragile anode wires having a diameter of only 10 μm and therefore they are vulnerable. In the present work, a detector based on robust Thick Gaseous Electron Multiplier (THGEM) has been proposed. A numerical demonstration of THGEM-Multi Wire hybrid detector technology as a possible candidate for the new generation low-energy fission studies and their evaluation as a function of different possible geometric and electric configuration in low-pressure gas is discussed here.

We have investigated the synthesis of superheavy elements using Cr-induced fusion reactions. We have studied all possible Cr-induced fusion reactions for the synthesis of super heavy nuclei [Formula: see text]. We have achieved the semi-empirical formula for fusion barrier heights ([Formula: see text]), positions ([Formula: see text]), curvature of the inverted parabola ([Formula: see text]) of Cr-induced fusion reactions for the synthesis of superheavy nuclei with atomic number range [Formula: see text]. The proposed formula produces fusion barriers of Cr-induced fusion reactions for the synthesis of super heavy nuclei with the simple inputs of mass number ([Formula: see text]) and atomic number ([Formula: see text]) of projectile-targets. We have also identified the targets for Cr-induced fusion reactions to synthesis superheavy elements of [Formula: see text]. We have also studied the entrance channel parameters such as mass asymmetry ([Formula: see text]), charge asymmetry ([Formula: see text]), coulomb interaction parameter ([Formula: see text]’), Businaro–Gallone mass asymmetry parameter ([Formula: see text]) and Isospin asymmetry parameter [[Formula: see text]]. We hope that our predictions may be the guide for the future experiments in the synthesis of more superheavy elements using [Formula: see text]Cr-induced fusion reactions.

The half-life and the [Formula: see text]-value of alpha decay in several super heavy elements are calculated. The nuclear potential is computed using the double-folding method. Using the S-matrix theory, the alpha decay is treated as a scattering problem between alpha particle and the daughter nucleus. Nuclear potential was approximated by the parameterized Woods–Saxon potential. This idea has also been extended to predict the half-life and the [Formula: see text]-value of the heaviest elements of few other alpha chains.

We presented the results of the series of experiments on the synthesis of Mc isotopes in the 243Am + 48Ca reaction performed at the new separator DGFRS-2 and cyclotron DC280 of the SHE Factory at FLNR JINR. There were registered 110 new 288Mc decay chains, 10 289Mc chains, and 4 287Mc chains. Alpha decay of 268Db with an energy of 7.6–8.0 MeV, half-life \(16_{{ - 4}}^{{ + 6}}\) h and α-branch \(51_{{ - 12}}^{{ + 14}}\% \) was registered for the first time together with a new spontaneously fissioning isotope 264Lr with a half-life of \(4.8_{{ - 1.3}}^{{ + 2.2}}\,\,{\text{h}}.\) The measured cross section of the 243Am(48Ca, 3n)288Mc reaction was \(17.1_{{ - 4.7}}^{{ + 6.3}}\) pb, which is the largest for known superheavy nuclei. A new isotope 286Mc was synthesized with a half-life of \(20_{{ - 9}}^{{ + 98}}\) ms and an α-particle energy of 10.71 ± 0.02 MeV. Spontaneous fission of 279Rg was first observed in one of the four new decay chains of 287Mc. The reaction excitation function was measured at six 48Ca energies in the range of 239–259 MeV, which led to the first observation of the 5n channel with a cross section of \(0.5_{{ - 0.4}}^{{ + 1.3}}\) pb. The decay properties of 20 previously known isotopes have been determined with higher accuracy.

Abstract The 20th century started with the realization that working together and collaborating expedites new discoveries. The Solvay Conference in 1911 brought together scientists to try to understand the real nature of matter, the new elements, and their properties. Through global conflicts, the scientists stayed in communication and organized IUPAC and IUPAP to stay current in advances internationally in chemistry and physics, respectively. The outcomes include the discovery and naming of the elements that complete the periodic table of elements and the chart of nuclides with the heavy atoms and all of their isotopes. Mary Lowe Good forged new directions in developing tools in the field of radiochemistry. She exemplified cooperation and collaboration nationally and internationally. Now the advances in the heavy elements by Yuri Ts. Oganessian and colleagues staying close to the principles of international cooperation and sharing the new information about the connection of the production of super heavy elements to the main part of the chart of nuclides. The future lies in determining whether there are more elements to be discovered and what are their chemical properties.

Cette thèse étudie le mécanisme de synthèse des éléments super-lourds (SHE) par des réactions de fusion-évaporation. Il s'agit de noyaux de numéro atomique \(Z \ge 104\) qui n'existent pas dans la nature en raison de leurs barrières de fission macroscopiques qui disparaissent. Ils sont stabilisés par une correction quantique du modèle en couches. La recherche de nouveaux SHE repousse les limites de la physique nucléaire et nous permet de mieux comprendre leur formation, leur stabilité et leur structure. Cependant, la synthèse des SHE est un défi en raison de la diminution des sections efficaces de production à mesure que la charge atomique augmente, ce qui nécessite des simulations théoriques pour guider les expériences et identifier les conditions de réaction optimales.Ce travail se concentre sur l'amélioration du pouvoir prédictif du modèle Kewpie2, conçu pour la simulation de la réaction de fusion-évaporation. Cette réaction est modélisée comme un processus en trois étapes : capture, formation et survie. Alors que Kewpie2 simule de manière indépendante la section efficace de capture et la probabilité de survie, il nécessitait des calculs externes pour la probabilité de formation. Cette thèse met en œuvre l'étape de formation dans le code Kewpie2 pour la première fois en utilisant à la fois les formalismes de sur-critiques et de Langevin complet. La distance du point d'injection (décrivant la configuration initiale de la phase de formation pour le système projectile-cible) est optimisée pour les réactions de fusion froide et chaudes séparément. Une paramétrisation améliorée de la distance du point d'injection, compatible avec le formalisme de Langevin, reproduit les sections efficaces de résidus d'évaporation mesurées pour les réactions de fusion chaude, généralement avec un ratio inférieur à un ordre de grandeur. Pour les réactions de fusion froide, les canaux d'émission de plusieurs neutrons sont expliqués par l'introduction d'un terme structurel supplémentaire, ce qui permet d'obtenir un bon accord avec les données expérimentales. Dans ce cas, les données du canal 1n sont décrites comme ayant une déviation d'un facteur par rapport aux données expérimentales, alors que pour les canaux 2n et 3n, les ratios sont à l'intérieur d'un ordre de grandeur. La thèse étudie également la modélisation de la probabilité de survie en utilisant les données les plus récentes pour SHE. Les étapes de formation et de survie sont testées de manière approfondie et comparées au modèle de fusion par diffusion (FbD) pour 27 réactions de fusion froide et 24 réactions de fusion chaude.L'analyse des coefficients de frottement réduits dans le cadre de l'approche de Langevin suramortie suggère que la dynamique n'est pas sur-critique. Par conséquent, un formalisme de Langevin unidimensionnel complet est étudié et implémenté dans Kewpie2. Le formalisme est appliqué aux données de réaction de fusion chaude. Les paramètres du modèle sont optimisés à l'aide d'une technique d'ajustement systématique, et les résultats confirment que la dynamique n'est pas sur-critique. Dans cette approche, les prédictions du modèle se situent dans un ordre de grandeur d'écart par rapport aux données expérimentales. Les prédictions pour la synthèse d'éléments de numéros atomiques ZCN = 119 et 120 s'accordent avec les résultats d'autres codes. En outre, une méthode d'étude des rapports de probabilités de formation est proposée et discutée pour la synthèse des isotopes 258No et 259Db.En conclusion, ce travail améliore considérablement Kewpie2, ce qui en fait un outil autonome pour l'étude de la synthèse SHE et l'orientation des futurs efforts expérimentaux
This thesis investigates the mechanism of synthesising super-heavy elements (SHE) via fusion evaporation reactions. These are nuclei with atomic numbers \(Z \ge 104\) and do not exist in nature due to their vanishing macroscopic fission barriers. They are stabilised by quantum shell correction. The search for new SHE pushes the boundaries of nuclear physics, furthering our understanding of their formation, stability, and structure. However, synthesising SHE is challenging due to decreasing production cross sections as the atomic charge increases, necessitating theoretical simulations to guide experiments and identify optimal reaction conditions.This work focuses on improving the predictive power of the Kewpie2 model, designed for fusion evaporation simulation. Fusion evaporation is modelled as a three-stage process: capture, formation, and survival. While Kewpie2 independently simulates the capture cross section and survival probability, it has relied on external calculations for formation probability. This thesis implements the formation step in the Kewpie2 code for the first time using both the overdamped and full Langevin formalisms. The injection point distance (describing projectile-target nuclei starting configuration) is optimised for cold and hot fusion reaction datasets in both cases. An improved injection point distance parametrisation, consistent with the Langevin formalism, reproduces measured evaporation residue cross sections for hot fusion reactions, typically with accuracy better than an order of magnitude. For cold fusion reactions, multiple neutron emission channels are explained by introducing an additional structural term, achieving good agreement with experimental data. In this case, the 1n channel data are described as having a factor deviation from the experimental data, while the 2n and 3n channels are within an order of magnitude. The thesis also investigates survival probability modelling using the latest data for SHE. Both the formation and survival steps are extensively tested and compared with the Fusion-by-Diffusion (FbD) model for sets of 27 cold and 24 hot fusion reactions.Analysis of the reduced friction coefficients within the overdamped Langevin approach suggests that the dynamic is not fully damped. Therefore, a full one-dimensional Langevin formalism is investigated and implemented in Kewpie2. The formalism is applied to hot fusion reaction data. The fitting coefficients of the model are optimised using a so-called systematic fitting technique, and the results confirm that the dynamic is not fully damped. In this approach, the model predictions are within an order of magnitude deviations from the experimental data. Predictions for the synthesis of elements with atomic numbers ZCN = 119 et 120 align with results from other codes. Additionally, a method for studying ratios of formation probabilities is proposed and discussed for the synthesis of 258No et 259Db..In conclusion, this work significantly enhances Kewpie2, making it a self-contained tool for studying SHE synthesis and guiding future experimental efforts

<div class="section abstract"><div class="htmlview paragraph">In India, , as per mandate of hon'ble Supreme Court of India for reduction of emission due to vehicles, compressed natural gas (CNG) powered city buses and passengers cars are in use since 2000. Their usage is limited to metropolitan cities like Delhi, Mumbai, Bangalore etc. due to limitation of CNG storage and dispensing infrastructure along with low energy density storage. High energy density liquid form of natural gas storage (LNG) can overcome these difficulties and promising in near future. Simultaneously, there is a need for development of efficient fuel storage system, fuel supply system, engine optimization &amp; calibration, engine lubricant etc. suitable for implementation of LNG for automotive application. In this background, the present work is aimed at the framework of engine testing facility, development of dedicated lubricant and performance of the engine for LNG application.</div><div class="htmlview paragraph">This paper describes LNG engine test lab standard operating procedure developed during the LNG internal combustion engine dynamometer testing programme. Due to safety requirement, it is neither advisable nor permissible to connect large LNG cryogenic tankers to engine test bench. Hence, state of the art small &amp; portable cryogenic LNG tank (450 Lit water capacity (WC)) comprised of vacuum and super insulated layered configuration manufactured as per International Organization for Standardization (ISO) 21029-1 and type tested according to ISO-12991 was designed as horizontal tank to transport LNG from large LNG cryogenic tanker to engine testing site. Bharat Stage (BS) VI emission standard complied LNG engine testing facility was developed and forced convection heat transfer methodology applied for avoiding icing at re-gasified liquefied natural gas (RLNG) fuel line.</div><div class="htmlview paragraph">This paper presents the development of dedicated lubricant for LNG fuelled heavy duty (HD) engine and establishment of oil drain interval and evaluation was done on 6-cylinder HD engine using LNG fuel. The engine was optimized for using LNG fuel. Initial performance of the engine using LNG was compared vis-à-vis CNG and, thereafter, the engine was subjected to endurance test of 1500 hours as per engine simulated driving cycle that closely represents road drive conditions to validate the technology and to establish the drain interval of lubricant. Further, to access the actual performance, limited field trials of 30,000 Km with LNG fuelled busses have been completed. It has been observed that LNG shows reduction of CO, THC and CH4 emissions and NOx emissions increased as compared to CNG. However, these values meet the BS VI emission norms. Oil sampling and analysis were undertaken after completion of every 100 hrs along with performance of the engine i.e. Power (kW), Torque (Nm) and brake specific fuel consumption (BSFC) (g/kWh) and emission characteristics. Engine performance was found satisfactory during endurance test. Developed engine oil demonstrated excellent behavior with LNG fuel and used engine oil physicochemical properties i.e. Kinematic viscosity@100°C, Total Base number (TBN), Total acid number (TAN), oxidation, nitration and wear elements (Iron (Fe), Copper (Cu), Aluminum (AL), Lead (Pb)) were reported well within the permissible limit. The study shows that the lubricant can be used for LNG application.</div></div>