原子核三分裂变

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The most probable outcome of the ternary fission is the emission of two heavy fragments and one light-charged particle. In about 90\%, these are $\alpha$ particles, which often referred to as the long-range alpha (LRA). Such decay has been extensively studied over decades in various heavy fissioning systems. The probability of such a process has been found to be about (2-4)$\times 10^{-3}$ relative to binary fission. The experimental data showed an increasing trend in the probability of such a process with an increase in fissility parameter within the range of 35 - 39. In the last decades, a region of the heaviest nuclei has been substantially expanded in both proton and neutron numbers. This includes neutron-deficient heavy and superheavy nuclei with fissility parameters, which are significantly exceeding the aforementioned range. In the present work, the currently available experimental data on the probability of the LRA emission, which is a representative of ternary fission, are discussed. The probabilities of LRA emission were calculated within the various empirical approaches, including the presently suggested semi-empirical expression. The latter one was derived on the basis of the $\alpha$-decay property of the fissioning nucleus. The results of all approaches discussed show that the probabilities of LRA emission are substantial (up to a percentage) in the fission of neutron-deficient heavy and superheavy nuclei.

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Within the framework of the quantum fission theory on the base of the mechanism of the intermediate nucleus formation in the virtual state, research continues on the experimental characteristics of prescission light nuclei for cases of ternary spontaneous and induced fission (with the participation of thermal neutrons) of heavy nuclei 252Cf and 235U, 239Pu, respectively. On the basis of Gamow's alpha-decay theory, the probabilities of the formation of ω_(n_3 ) nuclei in the parent nuclei were calculated. It was found that for the cases of the appearance of third particles in two types of fission (spontaneous and induced), such characteristics as the values of the yields δ_(n_3 ), the maxima of the experimental energy distributions T_(n_3 max), as well as the probabilities of formation of ω_(n_3 )obtained in this work for prescission light nuclei, are close.

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The distributions of ternary fission fragment’s energies have been presented for ³²S + ²³⁸U reaction at 220 MeV projectile energy, by developing a programming code based on simultaneous decay kinematics. Here, the energy distributions are shown for three different cases of angular arrangements of the fragments. The first case is for random distribution of angles and it is found that for fragment mass numbers 89, 82, and 77; the system releases the maximum amount of energy (247 MeV). On the other hand, among all three fragments, the third fragment (the lightest one), carries more than 200 MeV energy, and heaviest fragment carries the lowest amount of energy which is less than 40 MeV for most of the cases. The second case is the one where the angles of first (heaviest) and second (medium heavy) fragments are kept equal in both sides of beam direction and for this case, three fragment’s combinations (¹³²Sn + ⁷⁸Ni + ⁶⁰Zn, ¹⁴⁴Nd + ⁷⁸Ni + ⁴⁰Ca, and ¹³²Sn + ⁹⁸Sr + ⁴⁰Ca) has been considered by considering shell closure nuclei to see the energy distribution patterns. In the last case, where first and second fragments have been kept fixed at 50 degrees in both sides of the beam direction, it is found that third fragment decays toward the backward direction for all combinations carrying the maximum amount of energy among three fragments. Eventually, the total fragment’s energy for ¹³²Sn +⁷⁸Ni + ⁶⁰Zn, ¹⁴⁴Nd + ⁷⁸Ni + ⁴⁰Ca, and ¹³²Sn + ⁹⁸Sr + ⁴⁰Ca combinations are found to be 406 MeV, 403 MeV, and 419 MeV respectively. To recapitulate, it has been found that lighter fragments get the maximum amount of energies for all three cases and this method of calculating energies can be applied for any nuclear system that decays simultaneously into three fragments. Therefore, the result of this work is an important guide for experimental work on the evidence of ternary events by comparing energy distributions.

In the framework of trinuclear system (TNS) model, we investigate the formation of heavy fission isomers produced in spontaneous ternary fission of 252 Cf, and their decay while traversing the Cu foil, observed in Dubna experiments. After the first decay of TNS, the asymmetric DNS is formed introducing itself as a fission isomer in cluster state. The Coulomb interaction of this asymmetric DNS and foil nucleus Cu decreases the DNS decay barrier. The calculated half-lives of asymmetric DNS show a strong decrease when the DNS approaches to the foil nucleus Cu, supporting the experimental observations.

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It is proposed to measure the shift in the angular distribution of light charged particles (LCP) in ternary fission caused by polarized neutrons of plutonium isotopes in the resonance region with 𝐸𝑛 = 0.264 eV for the 241Pu target and 𝐸𝑛 = 0.294 eV for the 239Pu target. The reliability of interpretation of these experiments will compare favorably with measurements carried out previously at 𝐸𝑛 = 4.5 meV. The advantage is associated with a noticeable weakening of the influence of resonances, the parameters of which may raise some doubts. We are talking about resonances introduced at neutron energies 𝐸𝑛 < 0 eV. In addition, in the region of these two resonances, the fractions of impurity partial cross sections with a spin different from the spin of the resonance itself are small. It is important that the magnitude of the effects expected at the indicated resonance energies will be significantly greater than those previously obtained in the cold neutron energy region.

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We present our first results for a microscopic simulation of symmetric boost fission in terms of the antisymmetrized molecular dynamics (AMD) model. In AMD model, ground states of fissioning nuclei were prepared by a frictional cooling method and symmetrical boost momenta were given to nucleons inside to split the ground-state into fission fragments. After the simulation, we calculated the mass numbers and total kinetic energy (TKE) of the fission fragments. We also calculated orbital angular momenta of each fragment and identified them as spins, their mutual orientation and their orientation with respect to the linear momenta which defined the fission axis. Moreover, we found spin distribution of fission fragments was similar to the one given by the Fermi-gas model if spin cut-off parameter was adjusted. Finally, several ternary fission events were observed, emitting Tritium or 4He from the neck region, and average energy and angles of these ternary particles with respect to the fission axis were found to be in accord with experimental data.

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We present a freeze-out approach for describing the formation of heavy elements in expanding nuclear matter. Applying concepts used in modeling heavy-ion collisions or ternary fission, we determine the abundances of heavy elements taking into account in-medium effects such as Pauli blocking and the Mott effect, which describes the dissolution of nuclei at high densities of nuclear matter. With this approach, we search for a universal initial distribution in a quasi-equilibrium state from which the coarse-grained pattern of the solar abundances of heavy elements freezes out and evolves by radioactive decay of the excited states. The universal initial state is characterized by the Lagrange parameters, which are related to temperature and chemical potentials of neutrons and protons. We show that such a state exists and determine a temperature of 5.266 MeV, a neutron chemical potential of 940.317 MeV and a proton chemical potential of 845.069 MeV, with a baryon number density of 0.013 fm−3 and a proton fraction of 0.13. Heavy neutron-rich nuclei such as the hypothetical double-magic nucleus 358Sn appear in the initial distribution and contribute to the observed abundances after fission. We discuss astrophysical scenarios for the realization of this universal initial distribution for heavy-element nucleosynthesis, including supernova explosions, neutron star mergers and the inhomogeneous Big Bang. The latter scenario may be of interest in the light of early massive objects observed with the James Webb Space Telescope and opens new perspectives on the universality of the observed r-process patterns and the lack of observations of population III stars.

We investigate the ternary fissions of $^{252}$Cf (spontaneous) and $^{236}$U (neutron-induced) into medium-mass fragments, as reported by the Dubna group, using the Hartree-Fock plus BCS method with the SLy6 Skyrme interaction. Compared to microscopic-macroscopic methods used so far, this self-consistent approach provides a greater flexibility of nuclear shapes. Our working hypothesis is that the shape evolution proceeds while the system is still mononuclear. The results show that a ternary fission valley emerges for intermediate elongations of the middle fragment, only when its mass is strongly constrained. This ternary mode is dynamically suppressed by the competition with the dominant binary decay channel. This suggests that a description based solely on quantum tunneling through the energy barrier is insufficient to evaluate its probability. To quantify this suppression, we apply a simple Langevin-type model of overdamped motion with constant damping and temperature, supplemented by a basic estimate of quantum tunneling where relevant. Under assumptions expected to yield an upper bound, we find the probability of ternary fission per binary decay to be on the order of $10^{-8}-10^{-9}$ for $^{252}$Cf and $10^{-10}-10^{-11}$ for $^{236}$U.

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Numerous experimental and theoretical observations have concluded that the probability of the three fragment emission (ternary fission) or binary fission increases when one proceeds towards the heavy mass region of nuclear periodic table. Many factors affect fragment emission, such as the shell effect, deformation, orientation, and fissility parameter. Binary and ternary fissions are observed for both ground and excited states of the nuclei. The collinear cluster tripartition (CCT) channel of the U(n , f) reaction is studied, and we observe that the CCT may be a sequential or simultaneous emission phenomenon. To date, different approaches have been introduced to study the CCT process as a simultaneous or sequential process, but the decay dynamics of these modes have not been not fully explored. Identifying the three fragments of the sequential process and exploring their related dynamics using an excitation energy dependent approach would be of further interest. Hence, in this study, we investigate the sequential decay mechanism of the U(n , f) reaction using quantum mechanical fragmentation theory (QMFT). The decay mechanism is considered in two steps, where initially, the nucleus splits into an asymmetric channel. In the second step, the heavy fragment obtained in the first step divides into two fragments. Stage I analysis is conducted by calculating the fragmentation potential and preformation probability for the spherical and deformed choices of the decaying fragments. The most probable fragment combination of stage I are identified with respect to the dips in the fragmentation structure and the corresponding maxima of the preformation probability ( ). The light fragments of the identified decay channels (obtained in step I) agree closely with the experimentally observed fragments. The excitation energy of the decay channel is calculated using an iteration process. The excitation energy is shared using an excitation energy dependent level density parameter. The obtained excitation energy of the identified heavy fragments is further used to analyze the fragmentation, and the subsequent binary fragments of the sequential process are obtained. The three identified fragments of the sequential process agree with experimental observations and are found near the neutron or proton shell closure. Finally, the kinetic energy of the observed fragments is calculated, and the middle fragment of the CCT mechanism is identified.

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Collisions of actinide nuclei form, during very short times of few 10;{-21} s, the heaviest ensembles of interacting nucleons available on Earth. Such collisions have been proposed as an alternative way to produce heavy and superheavy elements. They are also used to produce superstrong electric fields by the huge number of interacting protons to test spontaneous positron-electron (e;{+}e;{-}) pair emission predicted by the quantum electrodynamics theory. The time-dependent Hartree-Fock theory is used to study collision dynamics of two 238U atomic nuclei. In particular, the role of nuclear deformation on collision time and on reaction mechanisms such as nucleon transfer is emphasized. The highest collision times (approximately 4 x 10;{-21} s at 1200 MeV) should allow experimental signature of spontaneous e;{+}e;{-} emission in case of bare uranium ions. Surprisingly, we also observe ternary fission due to purely dynamical effects.

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The neutron richness of the light charged particles emitted out of the fission plane in heavy ion reactions has been experimentally investigated via the production of A=3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$A=3$$\end{document} mirror nuclei in 86\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{86}$$\end{document}Kr +nat\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\textrm{nat}$$\end{document}Pb reactions at 25 MeV/u. The energy spectra and angular distributions of triton (t) and 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^3$$\end{document}He in coincidence with two fission fragments are measured with the Compact Spectrometer for Heavy IoN Experiment (CSHINE). The energy spectrum of 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{3}$$\end{document}He is observed harder than that of triton in the fission events, in accordance with the phenomena reported as “3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{3}$$\end{document}He-puzzle” in inclusive measurements. With a data-driven energy spectrum peak cut scenario, it is observed that the yield ratio R(t/3He)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R(\mathrm{t/^3He})$$\end{document} increases with the angle to the fission plane, showing an enhancement of neutron-rich particle emission from out-of-fission-plane. A qualitative comparison with the transport model calculations suggests that this observation may serve as a new probe for the nuclear symmetry energy.

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MicroMegas detectors are versatile gaseous detectors which are used for ionizing particle detection. A MicroMegas detector consists of two adjacent gas-filled volumes. One volume acts as a drift region with an electric field operating in the ionization chamber regime, the second volume is the amplification region acting as a parallel-plate avalanche counter. The use of the microbulk technique allows the production of thin, radiation resistant, and low-mass detector with a highly variable gain. Such MicroMegas detectors have been developed and used in combination with neutron time-of-flight measurements for in-beam neutron-flux monitoring, fission and light-charged particle reaction cross section measurements, and for neutron-beam imaging. An overview of MicroMegas detectors for neutron detection and neutron reaction cross section measurements and related results and developments will be presented.

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The Light-Charged Particle Detector Array (LPDA) operates at the Back-n white neutron source of the China Spallation Neutron Source (CSNS). The high neutron flux at Back-n causes event pile-up in the grid ionization chamber (GIC) of the LPDA. The particle identification method previously used for the 6Li(n, t)4He reaction channel ignored the events of two tritons being incident simultaneously, resulting in a systematic underestimation of particle yield. To address this issue, we propose a novel function g(E,R(E)) that relates particle energy E to ionization range R(E), which can be used to extract the proportion of double-triton from statistical distributions. Multi-parameter analysis in the neutron energy region from 0.3eV to 1MeV reveals that the double-triton events, the triton events and the invalid events constitute 3.4%, 94.6% and 2% of the total counts, respectively. This work validates the feasibility of resolving (n, cp) pile-up events under high-flux conditions, offering new approaches for detector designing in high-rate environments such as nuclear reactors or accelerator-driven systems.

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) provides neutrons in the continuous energy region from 0.5 eV to 200 MeV. A spectrometer named Light charged Particle Detector Array (LPDA) is designed for the study of (n, lcp) reactions at Back-n. The main detector of the LPDA spectrometer, a 16-unit ΔE-ΔE-E telescope array, is composed of two arrays of 8-unit ΔE-ΔE-E telescope. Each telescope unit consists of a Low-Pressure Multi-Wire Proportional Chamber (LPMWPC), a Si-PIN detector, and a CsI(Tl) scintillator detector. In 2021, a neutron-proton (n-p) scattering reaction cross-section measurement experiment was accomplished as the first experiment of the telescope array. Protons can be clearly identified in the ΔE-E spectrum (LPMWPC + Si-PIN) and the ΔE-E spectrum (Si-PIN + CsI(Tl)). Cross sections of the n-p scattering reaction in the neutron energy range of several MeV are extracted. The ΔE-E method also provides new measurement opportunities for many-body neutron induced light charged-particle emission reactions.

In recent years, particle discrimination methods based on digital waveform analysis techniques for neutron-transmutation-doped silicon (nTD-Si) detectors have become widely used for the identification of low-energy charged particles. Although the particle discrimination capability of this method has been well demonstrated for small incident angles, the particle discrimination performance may be affected by changes in the detector response when the detector is moved closer to the charged particle source and the incident position distribution and incident angle distribution to the detector become wide. In this study, we performed a beam test for particle discrimination in light-charged ($Z \le 2$) particles using the digital waveform analysis method with a pad-type nTD-Si detector and investigated the dependence of the performance of the particle discrimination on the incident position and incident angle. As the incident angle increased, a decrease in the maximum current was observed, which was sufficient to affect the performance of the particle discrimination. This decrease can be expressed as a function of the penetration depth of the charged particles into the detector, which varies for each nuclide.

In the past two decades cooperating with Frank Laboratory of Neutron Physics (FLNP), Joint Institute for Nuclear Research (JINR) measurements of (n, α) reaction cross sections for 6Li, 10B, 25Mg, 39K, 40Ca, 54,56,57 Fe, 58Ni, 63Cu, 64,67 Zn, 95Mo, 143Nd and 147,149 Sm nuclei were performed in the MeV neutron energy region based on the 4.5 MV Van de Graaff accelerator at Peking University. In recent years, our measurements were extended in three aspects. Firstly, measurements were expanded from two-body reactions to three-body reactions such as 10B (n, t2 α). Secondly, the neutron energy region was extended from below 8 MeV to 8 - 11 MeV by using the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE), with which cross sections of 54,56 Fe(n, α)53,51Cr reactions were measured. Thirdly, based on the newly-built China Spallation Neutron Source (CSNS) Back-n WNS (White Neutron Source), differential and angle-integrated cross sections for 6Li(n, t) and 10B(n, α) reactions were measured in the neutron energy region from 1 eV to 3 MeV.

We present recent experiments on an innovative alpha particle detection system, designed to investigate charged particle confinement and transport in high magnetic fields. Our test platform operates within a 3-T Siemens MRI superconducting magnet, providing a large cross-section (~ 40 cm diameter) for studying the behavior of charged particles in an aluminum vacuum can that is inserted into a uniform 3 T magnetic field. Using Americium-241 (241Am) sources placed inside this cylindrical vacuum chamber, we conducted simulations and experiments to measure and analyze alpha particle flux. This system enables the study of fundamental charged particle dynamics, which are relevant to a variety of applications, including nuclear propulsion concepts. Alpha particles serve as a surrogate for fission fragments due to their similar charge-to-mass ratio and comparable velocity, allowing us to explore key physical mechanisms that could influence the confinement and transport of fission fragments in future propulsion systems, specifically a fission fragment rocket engine (FFRE). This much more efficient nuclear rocket propulsion FFRE design was first proposed in the 1980s with the intent of greatly reducing transit times in long-duration space travel. Our objective is to enhance the operational efficiency of this nuclear rocket while gaining deeper insights into the behavior of fuel particles and of the fission-fragment ejecta within strong magnetic fields experimentally. The methodologies developed in this study establish a foundation for future experimental studies involving FFRE. More broadly, this work introduces a versatile approach for analyzing ion flux and nuclear reaction fragments across various experimental platforms.

A spectrometer for detecting charged particles has been developed, designed for high-precision research in nuclear physics and applied tasks. The instrument is based on a two-section ionization chamber with a Frisch grid, providing high detection efficiency, nearly isotropic solid angle (~4π), and minimal background noise levels, which is critically important for reliable determination of small reaction cross-sections. The relevance of this development is driven by growing interest in studying neutron-induced reactions related to nuclear energy development, radiation protection, and fundamental research into nuclear structure, as well as the lack of modern spectrometers capable of working with both solid and gaseous targets without loss of efficiency. The device is effectively used in systematic studies of charged particle emission reactions induced by fast neutrons on light and medium-mass nuclei. It enables obtaining energy distributions of reaction products, total and differential cross-sections, as well as angular distributions of charged particles. A key advantage of the spectrometer is its ability to work with both solid and gaseous samples, significantly expanding its application scope in scientific research.

The PADME experiment at LNF-INFN employs positron-on-target-annihilation to search for new light particles. Crucial parts of the experiment are the charged particle detectors, composed of plastic scintillator bars with light transmitted by wavelength shifting fibers to silicon photomultipliers (SiPMs). The location of the detector — close to a turbomolecular pump, inside a vacuum tank, and exposed to 0.5 T magnetic field — has driven the design of custom modular SiPM front-end and power supply electronics. The design of the system and its performance, confirming the desired sub-ns resolution on the reconstructed particle flying times, is shown and discussed.

This paper presents the results of neutron detection efficiency and dosimetry between a borated centrifugally tensioned metastable fluid detector (B-CTMFD) vs He-3 Ludlum-42-49B, and, the Fuji NSN3 conducted using a Cf-252 neutron source behind lead and concrete shielding. MCNP code simulations accounted for 3-D effects and derived cpm/mic.Sv/h factors. Ludlum and NSN3 offer fixed sensitivity, but CTMFD offered on-demand sensitivity by varying its Pneg state between 0.3-0.7 MPa. The B-CTMFD demonstrated sensitivity of up to ~22x greater than Ludlum and 5x greater than NSN3, for 0-15 cm Pb shielding, and 0-30 cm concrete shielding; it overcomes the 60% detection penalty inherent in the NB-CTMF-designed only to detect fast-energy neutrons - as described in the companion (Part-1) paper. Unlike the NB-CTMFD, which used 100% DFP (C5H2F10), the B-CTMFD requires the use of an azeotropic mixture of DFP, methanol, and tri-methyl borate (TMB - using natural boron) in 80:4:16 proportion. The B-CTMFD was about 6 times more sensitive than NB-CTMFD under the most heavily shielded condition and taken together, also offered 2-energy bin neutron spectroscopic enablement, together with 22-5x higher absolute efficiency- relative sensitivity compared with the non-spectroscopic Ludlum (He-3) and NSN3 (methane-nitrogen) based detectors. From an intrinsic efficiency standpoint, the B-CTMFD operating at Pneg = 0.7 MPa state, demonstrated even superior ~103x higher intrinsic efficiency over Ludlum and NSN3.

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A Monte Carlo simulation of the energy spectrum of the α particles emitted from a 238U3O8 sample is performed. Through comparing the simulated and measured energy spectra of the α particles, the non-uniformity of the 238U3O8 sample is obtained, and then the number of 238U target nuclei is determined. Using the obtained non-uniformity, a Monte Carlo simulation is developed to simulate the energy spectrum of neutron induced fission fragments. The simulated and measured energy spectra of neutron induced fission fragments agree well with each other.

The energy spectrum of prompt gamma-rays from 235U thermal fission is reproduced by a fission reaction model FIFRELIN to identify the origin of spectral features. This spectrum is characterized by a bump at 4-4.5 MeV, a shoulder at around 8 MeV, and a tail above 10 MeV, which are attributed to 132Sn and 133Sb, fission fragments with mass from 130 to 134, and those with mass from 99 to 104, charge from 40 to 42, and spin from 12 ℏto 16 ℏ, respectively. Among prompt gamma-rays, high-energy part is important to get insight into scission, because the quanta are emitted by highly excited fission fragments, which still keep the memory of the scission configuration. Our analysis suggests that coincidence detection of high energy gamma-rays and their source fission fragments identifying their isotopic species, spin and excitation energy with particular focus on those with mass number less than 104 will be useful to make conclusions about the origin of high energy gamma-rays.

The fission target detection system, which is based on U-235(or U-238)fission target and large area 4H-SiC detector, has been developed for pulsed neutron detection. However, calibration of its neutron energy response curve is challenging due to its very low detection efficiency to fast neutrons. In the past, the calibration of the neutron sensitivity for the fission target detection system was limited to using ∼ 14 MeV neutrons generated by the Cockcroft-Walton accelerator. To obtain the response function for the complete range of neutron energies, extrapolation based on neutron fission cross sections was required. In this paper, we present the calibration of its energy response at the China Spallation Neutron Source (CSNS) Back-n beam line using the time of flight method, both with double-bunch and single-bunch mode in end-station 1(with a flight path of ∼ 55 m). The SiC detector with a thin sensitive thickness of 30 μm has lower scattering background than the traditional Si-PIN detector . As a result, the energy response curve of the fission target detection system above 0.26 MeV has been successfully acquired. The spectrum of the double-bunch mode was unfolded using the Bayesian algorithm, and the results indicate that, under conditions of sufficient counts, this method can yield results similar to those obtained from the single-bunch mode. The issue of pulse height defect of SiC detector to fission fragments is discussed. This experiment confirms that our detection system of SiC+fission target has a strong signal-to-noise ratio and anti-interference capability. At the same time, it demonstrates that this device has its own advantages in measuring the energy response of low sensitivity detectors.

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The shift of the angular distribution of different light charged particles in ternary fission of 235U induced by polarized neutrons, the so-called ROT effect, was estimated by modified trajectory calculations, which take into account the rotation of the compound nucleus. In previous publications only α-particles were considered. It is shown here that inclusion of tritons significantly improves the agreement of the energy dependence of the ROT effect with experiment while the inclusion of 5He particles practically does not influence this dependence. In particular, the change in the magnitude of the ROT effect depending on the energy of incident neutrons is correctly predicted. Also, the ROT effect for gamma quanta and neutrons in binary fission is discussed along the same lines, because all mentioned effects are proportional to the effective angular velocity of the compound nucleus at the moment of scission.

An experimental study of rare fission modes of ${ }^{252}$ Cf was conducted using a hybrid pixel detector system based on Timepix technology. The primary objective was to investigate quaternary fission events, particularly those involving the decay of unstable light charged particles, such as excited states of ${ }^{7} \mathbf{L i}$ and ${ }^{8} \text{Be}$. The detection setup consisted of a $\Delta \mathrm{E}$ detector $(15 \mu \mathrm{m}$ thick) placed in front of $300 \mu \mathrm{m}$ thick Timepix sensor, offering high spatial resolution $(<10 \mu \mathrm{m})$ and per-pixel energy sensitivity. This configuration enabled the precise reconstruction of angular correlations and decay kinematics, significantly exceeding the capabilities of conventional silicon detectors. In addition to the traditional $\Delta E-E$ technique, detailed cluster analysis was performed using pattern recognition methods to identify charged particles, reconstruct their energy, and infer the parent isotopes. Two identical telescopes were positioned face-to-face at a distance of 2 cm from the ${ }^{252} \text{Cf}$ source, covering a limited angular range of about $3^{\circ}-5^{\circ}$ and $140^{\circ}-180^{\circ}$ for the opening angles between coincident LCPs. Due to this restricted geometry, Monte Carlo simulations were done to correct geometrical acceptance and detector response. Trajectory-based angular distribution calculations were also performed for the decay of unstable isotopes and compared with the experimental results.

The large angular and momentum acceptance magnetic spectrometer VAMOS++, at GANIL, France, is frequently used for nuclear structure and reaction dynamics studies. It provides an event-by-event identification of heavy ions produced in nuclear reactions at beam energies around the Coulomb barrier. The highly non-linear ion optics of VAMOS++ requires the use of the heavy ion trajectory reconstruction methods in the spectrometer to obtain the high-resolution definition of the measured atomic mass number. Three different trajectory reconstruction methods, developed and used for VAMOS++, are presented in this work. The performances obtained, in terms of resolution of reconstructed atomic mass number, are demonstrated and discussed using a single data-set of fission fragments detected in the spectrometer.