Fission Of Heavy Nuclei Research Articles

Dynamic Modeling of Clustering in Multimodal Fission of Heavy Nuclei

Dynamic Modeling of Clustering in Multimodal Fission of Heavy Nuclei

Formation mechanism of decay fragments in spontaneous ternary fission of heavy nuclei

A model for describing spontaneous ternary fission of heavy nuclei is presented. It follows from the suggested model that heavy nuclei have the same half-lives in spontaneous ternary and binary fission processes. The collinear cluster tripartition process observed in FOBOS experiments is found to be the dominant reaction channel in spontaneous true ternary fission of heavy nuclei within our model. Competition between binary fission and the formation of a trinuclear system, which is responsible for the ratio of spontaneous ternary and binary fission yields, is introduced.

Application of the cranking method to the semimicroscopic algebraic cluster model and nuclear molecules

A particular quantum phase transition (QPT) is studied at excited energies of light nuclei within the Semimicroscopic Algebraic Cluster Model (SACM), using a combination of catastrophe theory and a direct minimization of the potential. A distinct change from a compact nucleus to a nuclear molecule is described as a second order QPT occurring at a certain value of angular momentum. This finding is in accordance with experimental observations when nuclear molecules appear. The method has implication in the fission of heavy nuclei.

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

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

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.

Design Implementation and Parallel Operation of High-Current High-Power Multipulse Converters Feeding Nuclear Fuel Simulators

Nuclear reactors are designed to maintain a chain reaction producing a steady flow of neutrons generated by fission of heavy nuclei, such as uranium. They produce thermal energy, which is converted into mechanical energy and ultimately into electrical energy feeding to a grid network. In a nuclear reactor, fuel undergoes various power/temperature transients during normal and off -normal situations. One needs to simulate these transients in experimental facilities for performing variety of reactor engineering and safety related tasks. The facility consists of scaled thermal hydraulic test setup comprising process equipment, instrumented nuclear fuel channel simulator, and high current converters for feeding power equivalent to fission power to those simulators to handle the transients safely in controlled manner. The experimental results are used to generate database of various vital nuclear reactor process parameters under all types of operational transients and off -normal conditions that can be compared with predictions from computer codes thus validating ever-evolving and advanced software. Besides, simulation of severe accidental conditions of nuclear reactor in facility is also necessary for evaluation of thermal hydraulic design safety margin. A low-resistance fuel simulator of identical geometry with power scaling is directly heated by high dc current to simulate fission power for generating experimental database. The converters have capability to generate power/temperature transients for simulating nuclear reactor conditions. This article presents design, functional description, specifications, simulation, hardware implementation of 10 kA, 12-pulse, thyristorized converters powering fuel simulators. The successful implementation of parallel operation of four converters feeding 27 kA current is described in this article.

Some Thoughts on the Future of the Nuclear Energy Industry

Recent assessments of the strategic prospects of the nuclear energy industry tend to show a somewhat condescending attitude towards fusion, which, regretfully, has grounds given the current state of affairs in nuclear science. However, the analysis of the problems and the potentialities of the fusion of light nuclei and fission of heavy nuclei suggests that a full-scale development of each of the two nuclear technologies inevitably involves the need to overcome some formidable technological, materials science, environmental, and economic problems, some of which may put the feasibility of pursuing these nuclear energy programs at question. At the same time, the physical features of the fission and fusion processes objectively suggest that it may be reasonable to combine the two nuclear technologies within a joint nuclear energy system to enable a greater synergetic effect. This apparently would markedly lessen the problems attendant upon the application of each of the discussed technologies in the course of the full-scale development of nuclear energy.

A ROOT-based program for analysing T-odd asymmetry results of the neutron-induced fission of heavy nuclei

A ROOT-based program for analysing T-odd asymmetry results of the neutron-induced fission of heavy nuclei

Energy Outlook for Thermonuclear Fusion

Analysis of the problems and potential of two nuclear technologies based on fusion reactions of light nuclei and fission of heavy nuclei shows the following. Independent large-scale development of each one will make it necessary to overcome still unsolved technological, materials science, environmental, and economic problems, raising the question of the expediency of further development of these energy industries. At the same time, the physical features of the fission and fusion processes objectively indicate the expediency of combining them into a unified nuclear energy system, which will have a large synergistic effect. This will greatly mitigate the adverse aspects of each technology that will appear if the two systems develop independently. Calculations of neutron multiplication in the blanket of a hybrid thermonuclear reactor that confirm the physical feasibility and reliability of picking the direction of development in the form of a unified nuclear energy system are presented.

РАЗРАБОТКА МОДЕЛЕЙ, АЛГОРИТМОВ И ПРОГРАММНОГО КОМПЛЕКСА ДЛЯ РЕШЕНИЯ ЗАДАЧ ОЦЕНКИ РИСКА НА АЭС ПРИ ЗАПРОЕКТНЫХ АВАРИЯХ

A project is aimed at the development of models, algorithms and a program complex to carry out measures for safety increase and risk decrease during development of new nuclear power plants (NPP) and operation of working nuclear power ones. A basic novelty of the project is the development of a methodical apparatus for the estimate a radiation risk at NPP in case of the most dangerous (beyond-design) failures with the emission of origins of thermal neurons with the low density of a flow. 
 Atomic piles based on the use of fission energy of heavy nuclei fission are powerful sources of gamma and neuron radiation. The project is aimed at the computer modeling and development of new methods, algorithms and a program complex for the problem solution in the estimate of safety and risks at NPPs at the most dangerous (beyond-design) failures with the emission of thermal neurons sources with the low density of a flow. To realize the project it is necessary to develop a methodical approach to the solution of problems in the estimate of doses of external and internal irradiation and the estimate of damage for the population living around NPPs at the most dangerous (beyond-design failures with the emission of thermal neurons sources with the low density of a flow taking into account a population age structure. On the basis of these solutions there will be offered measures to decrease a risk and safety increase NPP safety.

An instrument for measuring T-odd asymmetries in the fission of heavy nuclei

We describe an experimental setup used to measure the T-odd asymmetry effects for prompt fission neutrons and γ-rays in binary fission of some heavy nuclei induced by polarized neutrons with resonance energy. The overall setup as well as the details of the design and performance of the key components like fission fragment detectors, neutron and γ detectors, and the electronics used in the data acquisition and processing system are presented. The experimental setup on beam line POLI of the FRM II reactor (Garching, Germany), as well as the neutron beam characteristics, polarization measurements are described, too.

SYNTHESIS REACTORS WITH USE OF ION ACCELERATORS

Nuclear reactors based on fission of heavy nuclei were created a decade after the discovery of uranium fission by neutrons. Attempts to create reactors based on synthesis of light nuclei have been continuing for more than seven decades. The main direction of their implementation repeats natural technologies - implementation of reactions under the influence of high (stellar) temperatures. This direction has faced a lot of problems, and in the modern sense requires huge investments for its implementation. There are developments based on the use of accelerator technology. In this paper, there is an assessment of feasibility to create synthesis reactors using colliding ion beams of the D-D, D-T, D-3He reactions. The technical solutions applicable for their implementation are shown, advantages of such reactors over thermonuclear reactors, possibility of producing fuel for them and the problems that arise.

Clusterization in heavy cold nuclei

A cluster is broadly understood to be an object which keeps its identity in a larger scale system. Manifestations of clustering can be revealed in very different size systems from exotic nuclei to galaxies. In our work we search for cluster effects in low energy fission of heavy nuclei. In the series of experiments carried out with the spectrometers based both on the gas filled (FOBOS spectrometer and its modifications) detectors and mosaics of solid-state detectors (setups at the beams of alpha-particles and deuterons, COMETA spectrometer) using the “missing mass” method and with the direct detection of three decay partners, we have discovered a new type of the ternary decay of heavy nuclei dubbed by us “collinear cluster tri-partition (CCT)”. The most interesting aspects of both the original methodic used and the physics of the effect observed are discussed in the presented report.

Odvrácená strana legendy: Otto Hahn v kontextu nacistického Německa

The article aims to demystify a long-standing legend about Otto Hahn, who, as the Nobel Prize winner for chemistry for the discovery of the fission of heavy nuclei, is widely regarded as an academic figurehead in the world of science. He was considered a symbol of so-called German decency and responsibility; he was a model example of an anti-Nazi scientist who did not collaborate with the criminality of the regime in its warmongery. It was only from the 1990s onwards that historians gained access to new archival materials, which allowed for a comprehensive picture of Hahn’s work in Nazi Germany and his involvement in uranium research during wartime, whose aim was construction of nuclear reactors and bombs.

Nuclear and chemical characterization of heavy actinides

Abstract Recent progress in the production of heavy nuclei far from stability and in the studies of nuclear and chemical properties of heavy actinides is briefly reviewed. Exotic nuclear decay properties including nuclear fission of heavy nuclei, measurements of first ionization potentials of heavy actinides, and redox studies of heavy actinides are described. Brief history of discovery of the transuranium elements is also presented.

Test of isospin conservation in thermal neutron-induced fission of $$^{245}\mathrm{Cm}$$ 245 Cm

We have recently shown that the general trends of partition-wise fission fragment mass distribution in heavy-ion-induced compound nuclear (CN) fission of heavy nuclei can be reproduced reasonably well by using the concept of isospin conservation, hence providing a direct evidence of isospin conservation in neutron-rich systems [Jain et al, Nucl Data Sheets 120, 123 (2014); Garg and Jain, Phys. Scr. 92, 094001 (2017); Jain and Garg, EPJ Web of Conference 178, 05007 (2018); Garg et al, Phys. Scr. 93, 124008 (2018)]. In this paper, we test the concept of isospin conservation to reproduce the fission fragment mass distribution emerging from thermal neutron-induced CN fission reaction, $$^{245}\mathrm{Cm}(n_{\mathrm{th}}, \hbox {f})$$ . As earlier, we use Kelson’s conjectures [I Kelson, Proceedings of the Conference on Nuclear Isospin (Academic Press, New York, 1969)] to assign isospin to neutron-rich fragments emitted in fission, which suggest the formation of fission fragments in isobaric analogue states. We calculate the relative yields of neutron-rich fragments using the concept of isospin conservation and basic isospin algebra. The calculated results reproduce the experimentally known partition-wise mass distributions quite well. This highlights the usefulness of isospin as an approximately good quantum number in neutron-rich nuclei. This also allows us to predict the fragment distribution of the most symmetric Cd–Cd partition and the heavier mass fragment distributions, both not measured so far.

Цифровое нейтрон/гамма разделение с органическим сцинтиллятором

The paper presents the results of neutron-gamma discrimination using organic stilbene scintillator. Stilbene scintillations are characterized by a fast rise time (~1 ns), and their decline is characterized by the existence of a fast (for compton electrons from gamma-quanta) and a slow (for recoil protons from fast neutrons) component. A well-known PSD (pulse shape discrimination) method of simultaneous measurement of the total charge and the part of this charge in the tail of the pulse, is proposed for identifying particles. An analog-to-digital converter of the TsRS-32 type was used to convert neutron and gamma-ray pulses and to store them in a digital format. An algorithm has been developed in the C ++ and ROOT programming languages for digital data processing. Stilbene-based detectors are planned to be used in an experiment to study T-odd effects for given particles in the fission of heavy nuclei induced by polarized neutrons. Experimental work was carried out in the I.M. Frank Laboratory of Neutron Physics Joint Institute for Nuclear Research.

Fusion: a true challenge for an enormous reward

Nuclear physics shows that energy can be released from both fission of heavy nuclei and fusion of light nuclei. Steady progress shows that fusion — an important additional option for energy production in the future — promises to be a clean and safe solution for mankind’s long-term energy needs with minimal environmental impact. A source of energy which would be inexhaustible, inherently safe and environmentally friendly, is this not a marvellous prospect? Nuclear fusion, a possible candidate for this role, has been the energy source of our Sun and the stars in the universe for billions of years. This process requires temperatures of tens of millions of degrees, so extremely high and foreign to our daily experience that it seems out of reach. Nevertheless, these extremely high temperatures are routinely realised in several laboratories all over the world, and since the early 1990s, tens of MW fusion power have been released from fusion reactions. We are witnessing the birth of a new technology destined to meet the gigantic future energy needs of mankind with minimal impact on the environment.

Measurement of the ROT effect in the neutron induced fission of 235U in the 0.3 eV resonance at a hot source of polarized neutrons

The TRI and ROT asymmetries in fission of heavy nuclei have been extensively studied during more than a decade. The effects were first discovered in the ternary fission in a series of experiments performed at the ILL reactor (Grenoble) by a collaboration of Russian and European institutes, and were carefully measured for a number of fissioning nuclei. Later on, the ROT effect has been observed in the emission of prompt gamma rays and neutrons in fission of 235U and 233U, although its value was an order of magnitude smaller than in the α-particle emission from ternary fission. All experiments performed so far are done with cold polarized neutrons, what assumes a mixture of several spin states, the weights of these states being not well known. The present paper describes the first attempt to get “clean” data by performing the measurement of gamma and neutron asymmetries in an isolated resonance of 235U at the POLI instrument of the FRM2 reactor in Garching.

Investigation of the heavy nuclei fission with anomalously high values of the fission fragments total kinetic energy

Binary fission of 232Th and 238U induced by fast neutrons were under intent investigation in the IPPE during recent years. These measurements were performed with a twin ionization chamber with Frisch grids. Signals from the detector were digitized for further processing with a specially developed software. It results in information of kinetic energies, masses, directions and Bragg curves of registered fission fragments. Total statistics of a few million fission events were collected during each experiment. It was discovered that for several combinations of fission fragment masses their total kinetic energy was very close to total free energy of the fissioning system. The probability of such fission events for the fast neutron induced fission was found to be much higher than for spontaneous fission of 252Cf and thermal neutron induced fission of 235U. For experiments with 238U target the energy of incident neutrons were 5 MeV and 6.5 MeV. Close analysis of dependence of fission fragment distribution on compound nucleus excitation energy gave us some explanation of the phenomenon. It could be a process in highly excited compound nucleus which leads the fissioning system from the scission point into the fusion valley with high probability.