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The present study focuses on investigating the shape evolution of neutron-rich even-even osmium (Os) transitional nuclei within the range of neutron number N = 82 to N = 190. The investigation is conducted using density-dependent meson-nucleon and point-coupling models within the framework of the covariant density functional theory (CDFT). Additionally, the results obtained from the CDFT calculations are compared with those obtained using the relativistic mean-field model with a nonlinear meson-nucleon interaction. The potential energy curve for Os isotopes (ranging from 158 Os to 260 Os) is analyzed in order to identify phase shape transitions, such as oblate-spherical-prolate. Furthermore, ground state bulk properties are calculated to gain insights into the structure of Os isotopes. The self-consistent calculations reveal a clear shape transition in the even-even Os isotopes, and overall, good agreement is observed among the different models employed as well as with the available experimental data. [ABSTRACT FROM AUTHOR]

Formation of neutron clusters from strongly correlated neutrons has become one of the hottest topics in nuclear physics. They lie at the heart of understanding the exotic structure of nuclei around the neutron drip line and provide an important basis for testing nuclear interactions due to the absence of Coulomb interaction and further developing theoretical models. Moreover, neutron clusters composed purely of neutrons could serve as a mini prototype of neutron matter to study the still elusive properties of the extremely neutron-rich nuclear matter, building a bridge between finite nuclei and neutron stars. In this paper, we will briefly review the recent highlights of experimental and theoretical works on neutron clusters.

This article is devoted to the description of the properties of the lightest nuclei with a large excess of neutrons. Light nuclei have always attracted attention due to the wide variety of their properties. While the structural characteristics of medium and heavy nuclei vary fairly smoothly, only single deviations are observed, the structure of light nuclei varies sharply, two neighboring light nuclei are often completely different from each other. This, on the one hand, makes their study a very interesting task, and on the other hand it makes it difficult to identify common trends. Our interest in light neutron-rich nuclei is connected with the desire to observe the characteristic features of nuclei overloaded with neutrons.

The availability of new radioactive ion beams has broadened the study of nuclear reactions and nuclear structure. The main mechanism to produce the secondary beams is the fragmentation of the projectile. An alternative method for the production of the exotic nuclei is the multinucleon transfer. We measured production cross section for the B, C, N and O isotopes in the reaction18O + Ta and the beam energy at 10 MeV/nucleon. The cross sections were obtained by integrating the momentum distributions of the isotopes. It was shown that in deep inelastic processes the production yields of different isotopes could be well described using statistical models and could also be explained by the Qgg-systematic.

Predictions of nuclear properties far from measured data are inherently inaccurate because of uncertainties in our knowledge of nuclear forces and in our treatment of quantum many-body effects in strongly-interacting systems. While the model bias can be directly calculated when experimental data is available, only an estimate can be made in the absence of such measurements. Current approaches to compute the estimated bias quickly lose predictive power when their input variables are taken far from the training region, resulting in uncontrolled uncertainties in applications such as nucleosynthesis simulations. In this letter, we present a novel technique to identify the input variables of machine learning algorithms that can provide robust estimates of model bias. Our process is based on selecting input variables, or features, based on their probability distribution functions across the entire nuclear chart. We illustrate our approach on the problem of quantifying the model bias in nuclear binding energies calculated with Density Functional Theory (DFT). We prove that building model biases with only Z and N as features leads to highly unreliable extrapolations. Conversely, we show that proper feature selection can systematically improve theoretical predictions without increasing uncertainties.

Multinucleon transfer reactions, characterized by the exchange of many nucleons at energies in the vicinity of the Coulomb barrier, have been extensively used in the last decades to understand the production of neutron-rich nuclei, as well as to study their structure. In this Mini Review, recent results related to the production mechanism of heavy neutron-rich nuclei obtained with stable and radioactive beams will be discussed together with the results concerning the proton transfer channels. Additionally, newest results from a series of experiments carried out to study nucleon-nucleon correlations for closed-shell and superfluid systems employing the large solid angle magnetic spectrometer PRISMA will be summarized.

The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher cross-sections. The main drawback of this technique is the wide angular distribution of the transfer products, which makes it challenging to catch and prepare them for precision measurements. To overcome this obstacle, we are building the NEXT experiment: a solenoid magnet is used to separate the different transfer products and to focus those of interest into a gas-catcher, where they are slowed down. From the gas-catcher, the ions are transferred and bunched by a stacked-ring ion guide into a multi-reflection time-of-flight mass spectrometer (MR-ToF MS). The MR-ToF MS provides isobaric separation and allows for precision mass measurements. In this article, we will give an overview of the NEXT experiment and its perspectives for future actinide research. [ABSTRACT FROM AUTHOR]

In the present study, the fusion reactions induced by neutron-rich nuclei have been investigated using the improved quantum molecular-dynamics (ImQMD) model. First, the accuracy of the results was determined by using a set of parameters IQ3a for 16O+92Zr, 40Ca+46Ti and 16O+154Sm fusion excitation functions. The obtained results revealed that the measured fusion excitation function can be reasonably well reproduced. A comparison was also performed with the theoretical results based on the coupled-channel calculations. Then, the time evolution of densities for the 16O+59Co and 32S+92Zr reactions in which the target nuclei were neutron-rich were studied and the fusion cross sections were calculated dynamically. It was found that the fusion cross sections of these reactions at energies around the Coulomb barrier can be well reproduced by using the ImQMD modle.

Using the reaction 7Li(7Li,10C) we tried to populate states in the tetraneutron. A peak in the energy spectrum of identified 10C, which we cannot attribute to a reaction with any other of the target components, corresponds to an excitation of the 10C+4n system of 2.93±0.16 MeV. Under different kinematic conditions an equivalent peak was observed. For a binding energy of the tetraneutron of −2.93 MeV a much larger width than the observed upper limit of Γ

We investigate 15 different Skyrme-interaction parametrizations and apply them to the chains of Te, Xe, Ba, Ce, Nd, Sm, Gd, Dy, Er, and Yb isotopes beyond N = 78 to calculate theoretical binding energies within the mean-field approach based on density functional theory. Results of calculations are compared with available experimental data on binding energies and quadrupole deformation with the aim to find out which interaction is the most convenient for shape and structure studies of these isotopic chains. [ABSTRACT FROM AUTHOR]

The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher cross-sections. The main drawback of this technique is the wide angular distribution of the transfer products, which makes it challenging to catch and prepare them for precision measurements. To overcome this obstacle, we are building the NEXT experiment: a solenoid magnet is used to separate the different transfer products and to focus those of interest into a gas-catcher, where they are slowed down. From the gas-catcher, the ions are transferred and bunched by a stacked-ring ion guide into a multi-reflection time-of-flight mass spectrometer (MR-ToF MS). The MR-ToF MS provides isobaric separation and allows for precision mass measurements. In this article, we will give an overview of the NEXT experiment and its perspectives for future actinide research.

The energy dissipation processes in multinucleon transfer reactions of 136Xe+198Pt at incident energies Elab=5.59 and 7.98 MeV/nucleon are investigated by using the improved quantum molecular dynamics model. The total-kinetic-energy-mass (TKE-Mass) distributions, the total kinetic energy loss (TKEL) distributions, and the excitation energy distributions of the primary binary products under different contact time scales of the reaction partners are analyzed. It shows that the value of the energy dissipation has an increasing trend over contact time. The quasielastic, the deep-inelastic, and the quasifission events can be roughly distinguished by the contact time. By analysing the correlation between the isotopic cross sections and the contact time, we find that the neutron-rich nuclei are produced in the deep-inelastic collisions.

Aiming to produce new neutron-rich nuclei at N = 126, the multi-nucleon transfer reactions 136Xe+194Ir, 208Pb are investigated by using the GRAZING model and the three-dimensional time-dependent Hartree-Fock (TDHF) approach. Deexcitation processes of the primary fragments are taken into account in both models. Comparison with the experimental data of 136Xe+208Pb at Ec.m. = 450 MeV indicates that the isotopic production cross sections around the entrance channel can be well reproduced by both models. The results of GRAZING indicate that 136Xe+194Ir is a promising candidate for producing new neutron-rich isotones with N = 126. The limitation of using TDHF to investigate multi-nucleon transfer reactions is also discussed.

The neutron, proton, and matter densities of the ground state of the 14B and 17C exotic nuclei are analyzed using the binary cluster model (BCM). Two density parameterizations are used in BCM calculations namely; Gaussian (GS) and harmonic oscillator (HO) parameterizations. According to the calculated results it found that, the BCM gives a good description of the nuclear structure for above neutron-rich exotic nuclei. The elastic form factors of the unstable 14B and 17C exotic nuclei and those of their stable isotopes 10B and 13C are determined using the plane-wave Born approximation. The main difference between the elastic form factors of unstable nuclei and their stable isotopes is due to the difference in the center of mass correction. Moreover, the Glauber model is used to calculate the matter rms radii and reaction cross section of these exotic nuclei. The calculate results of the mentioned nuclei give a good accordance with the experimental data. [ABSTRACT FROM AUTHOR]

We studied the charge radius ( r c ), neutron radius ( r n ), and neutron skin-thickness (Δ r = r n − r p ) over a chain of isotopes from C to Zr with the stable region to the neutron drip line. Theoretical calculations are done with axially deformed self-consistent relativistic mean-field theory (RMF) and effective nonlinear NL3 and NL3* interactions. The theoretically estimated values are compared with available experimental data and a reasonable agreement is noted. We additionally assessed the two-neutron separation energy ( S 2 n ) to mark the drip line nuclei of the considered isotopic series. In the reference of S 2 n , neutron magicity is also discussed. The calculated neutron radii are compared with empirical estimation made by r = r 0 N 1 / 3 to examine the abnormal trend of the radius for neutron drip line nuclei. In view to guide the long tails, the density distribution for some skin candidates is analyzed. Finally, neutron skin thickness is observed for the whole considered isotopic series. [ABSTRACT FROM AUTHOR]

Neutron-rich Sr nuclei around N=60 exhibit a sudden shape transition from a spherical ground state to strongly prolate-deformed. Recently, much new insight into the structure of Sr isotopes in this region has been gained through experimental studies of the excited levels, transition strengths, and spectroscopic factors. In this work, a “classic” shell model description of strontium isotopes from N=50 to N=58 is provided, using a natural valence space outside the 78Ni core. Both even–even and even–odd isotopes are addressed. In particular, spectroscopic factors are computed to shed more light on the structure of low-energy excitations and their evolution along the Sr chain. The origin of deformation at N=60 is mentioned in the context of the present and previous shell model and Monte Carlo shell model calculations.

Time-dependent Hartree-Fock (TDHF) theory has been a powerful tool in describing a variety of complex nuclear dynamics microscopically without empirical parameters. In this contribution, recent advances in nuclear dynamics studies employing TDHF and its extensions are briefly reviewed, in line with the study of multinucleon transfer (MNT) reactions. The latter lies at the core of this Research Topic, whose application for the production of extremely neutron-rich nuclei has been extensively discussed in recent years. Having in mind the ongoing theoretical developments, it is envisaged how microscopic theories may contribute to the future MNT study.

The radial wave functions of the Harmonic Oscillator and Woods-Saxon potentials within the three-body [two-body] model of Core + 2n [Core + n ] have been used to study some of the basic structural features such as the ground state proton, neutron and matter densities, the associated root mean square (rms) radii and elastic form factors of neutron-rich 17B [22N] halo nucleus. The long tail manner is clearly shown in the results obtained of neutron and matter densities of these nuclei. According to the calculated results it is found that this model provides a good description on the nuclear structure of above exotic nuclei. The reaction cross sections for these nuclei have been studied using the Glauber model with an optical limit approximation at high energy region. [ABSTRACT FROM AUTHOR]

Predictions are presented for proton skins based on isospin-asymmetric equations of state derived microscopically from high-precision chiral few-nucleon interactions. Moreover, the relation between the neutron skin of a nucleus and the difference between the proton radii of the corresponding mirror nuclei is investigated.

We explore the systematics of ground-state and excitation energies in singly-strange hypernuclei throughout the helium and lithium isotopic chains — from He Λ 5 to He Λ 11 and from Li Λ 7 to Li Λ 12 — in the ab initio no-core shell model with importance truncation. All calculations are based on two- and three-baryon interaction from chiral effective field theory and we employ a similarity renormalization group transformation consistently up to the three-baryon level to improve the model-space convergence. While the absolute energies of hypernuclear states show a systematic variation with the regulator cutoff of the hyperon–nucleon interaction, the resulting neutron separation energies are very stable and in good agreement with available data for both nucleonic parents and their daughter hypernuclei. We provide predictions for the neutron separation energies and the spectra of neutron-rich hypernuclei that have not yet been observed experimentally. Furthermore, we find that the neutron drip lines in the helium and lithium isotopic chains are not changed by the addition of a hyperon. [ABSTRACT FROM AUTHOR]

The characteristics of two modifications of the semiconductor (s.c.d.) setup consisting of telescopes on the basis of silicon detectors are presented. These settings allow performing a precision measurement of energy in a large dynamic range (from a few to hundreds of MeV) and particle identification in a wide range of masses. The issues of measurement of the characteristics of s.c.d. telescopes and their impact on the quality of the obtained experimental data are considered. Considerable attention is paid to the use of created semiconductor devices for the search for and spectroscopy of light exotic nuclei on the accelerators of PNPI (Gatchina) and LANL (Los Alamos). [ABSTRACT FROM AUTHOR]

A new technique to measure the lifetime τ of a neutron-radioactive nucleus that decays in-flight via neutron emission is presented and demonstrated utilizing MonteCarlo simulations. The method is based on the production of the neutron-unbound nucleus in a target, which at the same time slows down the produced nucleus and the residual nucleus after (multi-) neutron emission. The spectrum of the velocity difference of neutron(s) and the residual nucleus has a characteristic shape, that allows to extract the lifetime. If the decay happens outside the target there will be a peak in the spectrum, while events where the decay is in the target show a broad flat distribution due to the continuous slowing down of the residual nucleus. The method itself and the analysis procedure are discussed in detail for the specific candidate 26 O. A stack of targets with decreasing target thicknesses can expand the measurable lifetime range and improve the sensitivity by increasing the ratio between decays outside and inside the target. The simulations indicate a lower limit of measurable lifetime τ ∼ 0 . 2 ps for the given conditions. [ABSTRACT FROM AUTHOR]

Experimental data of β -decay half-lives of nuclei with atomic number between 20 and 190 are investigated. A systematic formula has been proposed to calculate β -decay half-lives of neutron-rich nuclei, with a particular consideration on shell and pair effects, the decay energy Q as well as the nucleon numbers (Z, N). Although the formula has relatively few parameters, it reproduces the experimental -decay half-lives of neutron-rich nuclei very well. The predicted half-lives for the r-process relevant nuclei obtained with the current formula serve as reliable input in the r-process model calculations. [ABSTRACT FROM AUTHOR]

For nucleosynthesis calculations of the r-process it is important to know beta-decay half-lives of short-lived neutron-rich nuclei. In the present paper these characteristics are calculated for an extended number of neutron-rich nuclei, important for the r-process. In our calculations the model description of beta-strength functions based on Finite Fermi-Systems Theory is used. The comparison with other predictions and experimental data is done. It is shown that the accuracy of beta-decay half-lives of short-lived neutron-rich nuclei is increasing with increasing neutron excess and can be used for modeling of nucleosynthesis of heavy nuclei in the r-process. For nuclei heavier than lead the half-lives of neutron-rich nuclei are on average 10 times smaller, than proposed of other predictions. [ABSTRACT FROM AUTHOR]

Predictions of nuclear properties far from measured data are inherently inaccurate because of uncertainties in our knowledge of nuclear forces and in our treatment of quantum many-body effects in strongly-interacting systems. While the model bias can be directly calculated when experimental data is available, only an estimate can be made in the absence of such measurements. Current approaches to compute the estimated bias quickly lose predictive power when their input variables are taken far from the training region, resulting in uncontrolled uncertainties in applications such as nucleosynthesis simulations. In this letter, we present a novel technique to identify the input variables of machine learning algorithms that can provide robust estimates of model bias. Our process is based on selecting input variables, or features, based on their probability distribution functions across the entire nuclear chart. We illustrate our approach on the problem of quantifying the model bias in nuclear binding energies calculated with Density Functional Theory (DFT). We prove that building model biases with only Z and N as features leads to highly unreliable extrapolations. Conversely, we show that proper feature selection can systematically improve theoretical predictions without increasing uncertainties. [ABSTRACT FROM AUTHOR]

Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics (ImQMD) model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the stability of an individual nucleus and the description of fusion cross sections at energies near the Coulomb barrier can be further improved. Simultaneously, the quasifission process in Sm+Gd is also investigated with the microscopic dynamics model for the first time. We find that at energies above the Bass barrier, the fusion probability is smaller than 10 for this reaction, and the nuclear contact time is generally smaller than 1500 fm/ c. From the central collisions of Sm+Gd, the neutron-rich fragments such as Gd, W can be produced in the ImQMD simulations, which implies that the quasi-fission reaction could be an alternative way to synthesize new neutron-rich heavy nuclei. [ABSTRACT FROM AUTHOR]

New experimental data on 2 energies of Sn confirm the trend of lower 2 excitation energies of even-even tin isotopes with N>82 compared to those with N<82. However, none of the theoretical predictions using both realistic and empirical interactions can reproduce experimental data on excitation energies as well as the transition probabilities ( $B(E2; 6^{+} \rightarrow 4^{+}$)) of these nuclei, simultaneously, apart from the ones whose matrix elements have been changed empirically to produce mixed seniority states by weakening the pairing. We have shown that the experimental result also shows good agreement with the theory in which three-body forces have been included in a realistic interaction. The new theoretical results on transition probabilities are discussed to identify the experimental quantities which will clearly distinguish between different views. [ABSTRACT FROM AUTHOR]

A combination of germanium detectors was installed at the PF1B neutron guide of the ILL to perform prompt spectroscopy of neutron-rich nuclei produced in the neutron-capture induced-fission of U and Pu. In addition, LaBr detectors from the FATIMA Collaboration were installed to complement with the EXOGAM clovers to measure lifetimes of low-lying excited states. The measured characteristics and online spectra indicate very good performances of the overall set-up. [ABSTRACT FROM AUTHOR]