Nuclei Mode Research Articles

Semiclassical description of wobbling and chiral modes in triaxial nuclei

A time-dependent variational principle with an angular momentum coherent state as a variational state, is used to describe the dynamics associated to a triaxial rotor Hamiltonian with rigidly aligned high-j quasiparticles. Solving the variational principle within a stereographic parametrization of the coherent state, one obtains a classical energy function and a set of canonical equations of motion expressed in terms of the azimuth angle and a canonical conjugate coordinate represented by the third projection of the total angular momentum. The system’s rotational dynamics is investigated through the evolution on total angular momentum of the canonical variables as well as spherical angles corresponding to minima of the constant energy surface. The unique minimum energy conditions are spin-dependent and define phases with specific dynamic behaviour. The transition between phases is investigated for a single and two aligned quasiparticle spins. The discrete energy levels and corresponding wave-functions are obtained through a quantization procedure applied to the classical energy function. The formalism is used for numerical applications to 135Pr and 134Pr nuclei.

Novel Excitation Modes in Nuclei: Experimental and Theoretical Investigation on Multiple Chiral Doublets

As a microscopic quantal many-body system, the structure of atomic nucleus is understood by measuring and interpreting its responses to all kinds of probes. The responses manifest in different kinds of energy excitation spectra with specific energy and angular momentum (spin), and link with electric and magnetic transition rates.

Primary emissions and secondary organic aerosol formation from in-use diesel vehicle exhaust: Comparison between idling and cruise mode

Diesel vehicle exhaust is an important source of carbonaceous aerosols, especially in developing countries, like China. Driving condition impacts diesel vehicle emissions, yet its influence needs further understanding especially on secondary organic aerosol (SOA) formation. In this study tailpipe exhaust from an in-use light duty diesel vehicle at idling and driving speeds of 20 and 40 km h−1 was introduced respectively into a 30 m−3 indoor smog chamber to investigate primary emissions and SOA formation during photo-oxidation. The emission factors of SO2 at 20 and 40 km h−1 were higher than those at idling, whereas the emission factors of aromatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs) and oxygenated volatile organic compounds (OVOCs) decreased when driving speeds increased. The emission factors of black carbon (BC) and primary organic aerosol (POA) at idling were comparable to those at 20 and 40 km h−1. The SOA production factors were 0.41 ± 0.09 g kg-fuel−1 at idling, approximately 2.5 times as high as those at 20 km h−1 (0.16 ± 0.09 g kg-fuel−1) or 40 km h−1 (0.17 ± 0.09 g kg-fuel−1). Total carbonaceous aerosols, including BC, POA and SOA, from diesel vehicles at 20 and 40 km h−1 were 60–75% of those at idling, due largely to a reduction in SOA production. Measured AHs and PAHs altogether were estimated to explain <10% of SOA production, and eight major OVOCs could contribute 8.4–23% of SOA production. A preliminary comparison was further made for the same diesel vehicle at idling using diesel oils upgraded from China 3 to China 5 standard. The emission factors of total particle numbers decreased by 38% owing to less nuclei mode particles, which was probably caused by the reducing fuel sulfur content; the emission factors of BC were almost unchanged, the POA emission factors and SOA production factors however decreased by 72% and 37%.

$\beta$(EC) delayed fission in the heaviest nuclei

Nuclear fission is one of the radioactive decay modes of heavy nuclei, and is a limiting factor in the existence of the superheavy elements. For decades, both experimental and theoretical works devoted to the study of fission have been performed, and are still ongoing. Among them, the so-called $\beta$ (electron capture)-delayed fission is of special interest. In this work, all known cases of electron-capture delayed fission in heavy nuclei were used to establish a semi-empirical approach that could quantitatively estimate the probability of the process. This framework was constructed based on a qualitative discussion of the fission-barrier shape, in contrast to a parabolic shape. The results show a strong effect of the fission-barrier shape on the delayed fission process. The predictions for yet unmeasured cases of electron-capture delayed fission in nuclei with atomic numbers in the wide range ( $79\leq Z\leq 119$) including the superheavy nuclei are given. It is suggested that $ \beta$-delayed fission manifests itself as one of the main decay modes of the superheavy nuclei, if $ \beta$ decay takes place.

Bayesian Neural Network improvements to nuclear mass formulae and predictions in the SuperHeavy Elements region

A systematic study based on the Bayesian Neural Network (BNN) statistical approach is introduced to improve the predictive power of current nuclear mass formulae when applied to nuclides not yet experimentally detected. In a previous work by the present authors, the methodology was introduced considering only the Duflo-Zuker mass model (Duflo J. and Zuker A., Phys. Rev. C, 52 (1995) R23) to explore the S uperH eavy E lements (SHE) region, with focus on the α-decay process. Due to the discrepancy among different mass formulae we decided to extend in the present calculation the application of the Bayesian Neural Network methodology to other mass formula models and to discussing their implications on predictions of SHE α-decay half-lives. The -value prediction using a set of ten different mass models has been greatly improved for all models when compared to the available experimental data. In addition, we have used the improved -value to determine the SHE α-decay half-lives with a well-succeeded model in the literature, currently employed for different hadronic nuclear decay modes of heavy nuclei, the E ffective L iquid D rop M odel (ELDM). Possible SHE candidates recently investigated are explicitly calculated (specially the 298, 299,300120 isotopes, and results present a promising via of research for these nuclei through α-decay process.

Soft breathing modes in neutron-rich nuclei with the subtracted second random-phase approximation

We analyze the isoscalar response related to breathing modes with particular attention being paid to low-lying excitations in neutron--rich nuclei. We use the subtracted second random--phase approximation (SSRPA) to describe microscopically the response. By increasing the neutron excess, we study the evolution of the response in Ca isotopes going from $^{40}$Ca to $^{48}$Ca and to $^{60}$Ca as well as in $N=20$ isotones going from $^{40}$Ca to $^{36}$S and to $^{34}$Si. Finally, the case of $^{68}$Ni is investigated. We predict soft monopole modes in neutron--rich nuclei which are driven by neutron excitations. At variance with dipole pygmy modes, these neutron excitations are not only strongly dominant at the surface of the nucleus but over its entire volume. The effect of the mixing with two particle-two hole configurations induced by the SSRPA model is analyzed. The properties of such soft neutron modes are investigated in terms of their excitation energies, transition densities and wave--function components. Their collectivity is also discussed as a function of the isospin asymmetry and of the mass of the nucleus. The link between such low--energy compression modes and a compressibility modulus introduced for neutron--rich infinite matter is finally studied.

Competition of rotation around the intermediate and long axes in Tl193

CITATION: Ndayishimye, J. 2019. Competition of rotation around the intermediate and long axes in 193Tl. Physical Review C, 100(1):014313, doi:10.1103/PhysRevC.100.014313.

ATOMIC NUCLEI AND QUARKS UNVEIL THEIR SECRETS

Because logic excludes that protons and neutrons have an outer layer to hold quarks together, there must by definition be a structural relationship between the quarks themselves to avoid jeopardizing the stability of the nucleus. To substantiate this, it is necessary to move away from the beaten track in an attempt to better understand the functioning of the nucleus and the atom as a whole. The structure of the nucleus of the atom has been re-mapped and spatially rearrangedand, in its simplicity, explains completely the inner workings of that atomic nucleus. It became immediately clear that it was only a small glimpse into a whole new world that has remained hidden so far and undoubtedly will open new fields of research in both physics and chemistry. The test of the validity of the reasoning behind the new way to approach the atomic nuclei and quarks is reinforced by explaining in detail the various decay modes of the atomic nuclei. Alpha decay, Beta plus decay, Beta minus decay, electron capture and nuclear fission are presented with detailed examples based on the new composition of the atomic nucleus. Although it seems rather technical at first, it is in reality a very elegant and easy-to-understand way how the mechanism of transformation of the structures of the atomic nucleus works. The current accepted theories that explain mass distribution of fission fragments through the liquid drop model, the shell model or the so-called unified model that brings the shell model and the liquid drop model together to explain certain magnetic and electric properties that neither of the two separately can explain, have been re-evaluated resulting in a logical and better diagnostic picture of the entire process.

Search for decay modes of heavy and superheavy nuclei * * Supported by the Turkish Science and Research Council (TÜBİTAK) with Grant Number 118R028

Spontaneous fission (SF) with a new formula based on a liquid drop model is proposed and used in the calculation of the SF half-lives of heavy and superheavy nuclei (Z= 90–120). The predicted half-lives are in agreement with the experimental SF half-lives. The half-lives of decay (AD) for the same nuclei are obtained by using the Wentzel-Kramers-Brillouin (WKB) method together with Bohr-Sommerfeld (BS) quantization condition considering the isospin-dependent effects for the cosh potential. The decay modes and branching ratios of superheavy nuclei (Z= 104-118) with experimental decay modes are obtained, and the modes are compared with the experimental ones and with the predictions found in the literature. Although some nuclei have predicted decay modes that are different from their experimental decay modes, decay modes same as the experimental ones are predicted for many nuclei. The SF and AD half-lives, branching ratios, and decay modes are obtained for superheavy nuclei (Z= 119–120) with unknown decay modes and compared with the predictions obtained in a previous study. The present results provide useful information for future experimental studies performed on both the AD and SF of superheavy nuclei.

Cluster radioactivity of Og176118294

According to theory, cluster radioactivity becomes an important decay mode in superheavy nuclei. In this work, we predict that the strongly-asymmetric fission, or cluster emission, is in fact the dominant fission channel for $^{294}_{118}$Og$_{176}$, which is currently the heaviest synthetic isotope known. Our theoretical approach incorporates important features of fission dynamics, including quantum tunneling and stochastic dynamics up to scission. We show that, despite appreciable differences in static fission properties such as fission barriers and spontaneous fission lifetimes, the prediction of cluster radioactivity in $^{294}_{118}$Og$_{176}$ is robust with respect to the details of calculations, including the choice of energy density functional, collective inertia, and the strength of the dissipation term.

Nuclear collective dynamics in the lattice Hamiltonian Vlasov method

The lattice Hamiltonian method is developed for solving the Vlasov equation with nuclear mean-field based on the Skyrme pseudopotential up to next-to-next-to-next-to leading order. The ground states of nuclei are obtained through varying the total energy with respect to the density distribution of nucleons. Owing to the self-consistent treatment of initial nuclear ground state and the exact energy conservation in the lattice Hamiltonian method, the present framework of solving the Vlasov equation exhibits very stable nuclear ground state evolution. As a first application of the new lattice Hamiltonian Vlasov method, we explore the iso-scalar giant monopole and iso-vector giant dipole modes of finite nuclei. The obtained results are shown to be comparable to that from random-phase approximation and consistent with the experimental data, indicating the capability of the present method in dealing with the long-time near-equilibrium nuclear dynamics.

Beta decay gets the ab initio treatment

One of the fundamental radioactive decay modes of nuclei is β decay. Now, nuclear theorists have used first-principles simulations to explain nuclear β decay properties across a range of light- to medium-mass isotopes, up to 100Sn.

Discrepancy between experimental and theoretical β-decay rates resolved from first principles

$\beta$-decay, a process that changes a neutron into a proton (and vice versa), is the dominant decay mode of atomic nuclei. This decay offers a unique window to physics beyond the standard model, and is at the heart of microphysical processes in stellar explosions and the synthesis of the elements in the Universe. For 50 years, a central puzzle has been that observed $\beta$-decay rates are systematically smaller than theoretical predictions. This was attributed to an apparent quenching of the fundamental coupling constant $g_A \simeq $ 1.27 in the nucleus by a factor of about 0.75 compared to the $\beta$-decay of a free neutron. The origin of this quenching is controversial and has so far eluded a first-principles theoretical understanding. Here we address this puzzle and show that this quenching arises to a large extent from the coupling of the weak force to two nucleons as well as from strong correlations in the nucleus. We present state-of-the-art computations of $\beta$-decays from light to heavy nuclei. Our results are consistent with experimental data, including the pioneering measurement for $^{100}$Sn. These theoretical advances are enabled by systematic effective field theories of the strong and weak interactions combined with powerful quantum many-body techniques. This work paves the way for systematic theoretical predictions for fundamental physics problems. These include the synthesis of heavy elements in neutron star mergers and the search for neutrino-less double-$\beta$-decay, where an analogous quenching puzzle is a major source of uncertainty in extracting the neutrino mass scale.

Synthesis and properties of isotopes of the transactinides

Abstract Isotopes of transactinide elements have to be synthesized in nuclear reactions with light or heavy beam particles. The efficient production by neutron capture and subsequent β − decay as it is used for the production of isotopes of actinide elements up to fermium is no longer possible due to the lack of suitable target material. The content of this article is about the synthesis and the study of the decay properties of nuclei to which atomic, respectively proton numbers from Z = 104 to 118 could be unambiguously assigned by physical means. The results identified the reaction products as isotopes of new elements beyond the actinides, the transactinides. As such the elements received names given by the discovers ranging from rutherfordium for element 104 to oganesson for element 118 which completes the 7th row of the Periodic Table of the Elements. Intensive heavy ion beams, sophisticated target technology, efficient electromagnetic ion separators, and sensitive detector arrays were the prerequisites for discovery of the elements from Z = 107 to 118 during the years from 1981 to 2013. The results and the techniques are described. Also given is a historical introduction into early experiments and the theoretical predictions for a possible existence of an island of stability located at the crossing of the next closed shells for the protons and neutrons beyond the doubly magic nucleus 208Pb. The experimental results are compared with recent theoretical calculations on cross-sections and decay modes of these superheavy nuclei, respectively isotopes of superheavy elements. An outlook is given on further improvement of experimental facilities which will be needed for exploration of the extension and structure of the island of superheavy nuclei, in particular for searching for isotopes with longer half-lives predicted to be located in the south east and for isotopes of further new elements expected in the north-east direction of the island at the upper end of the chart of nuclei.

Influence of biodiesel/diesel blends on particle size distribution of CI engine under steady/transient conditions

Biodiesel is considered as one of the most potential alternative fuels for transport sector. To better assess the overall effects of biodiesel application, an experimental study was conducted concerning the effects of rapeseed oil methyl ester (RME) and its blends with baseline diesel on particle size distribution (PSD) of a turbocharged compression-ignited (CI) engine under both steady and transient operating conditions. The influence of fuel-side combustion technique of using oxygenated additives on the transient particle emission was identified. Tests were carried out under constant engine speed and various load conditions, and controlled transient operation was employed for the transient study. The results show that biodiesel addition causes advanced start of combustion (SOC) under constant injection timing and higher in-cylinder pressure and heat release rate. Biodiesel has significant effects on the particle size distribution (PSD) under both steady-state and transient condition. For steady-state condition, the number concentration of carbonaceous particles (dp > 22 nm) decrease while that of non-carbonaceous particles (dp < 22 nm) increase with the increase of biodiesel proportion. For transient condition, biodiesel addition, as an oxygenated blending agent, can effective suppress the increase of carbonaceous particles but the nuclei mode particle increase dramatically during the load increasing process. In general, the oxygenated biodiesel is a very potential alternative of fossil fuel in constraining engine smoke opacity and particle emission under both steady-state and transient operating conditions. It is especially effective in reducing larger particles in the carbonaceous soot mode.

The effect of short range correlation on the inelastic C4 form factors of 18O nucleus

The effect of short range correlations on the inelastic longitudinalCoulomb form factors for different states of J   4 , T  1withexcitation energies 3.553,7.114, 8.960 and 10.310 MeV in 18O isanalyzed. This effect (which depends on the correlation parameter )is inserted into the ground state charge density distribution throughthe Jastrow type correlation function. The single particle harmonicoscillator wave function is used with an oscillator size parameter b.The parameters  and b are considered as free parameters, adjustedfor each excited state separately so as to reproduce the experimentalroot mean square charge radius of 18O. The model space of 18O doesnot contribute to the transition charge density. As a result, theinelastic Coulomb form factors of 18O comes absolutely from thecore polarization transition charge density. According to thecollective modes of nuclei, the core polarization transition chargedensity is assumed to have the form of Tassie shape. It is found thatthe introduction of the effect of short range correlations is necessaryfor obtaining a remarkable modification in the calculated inelasticlongitudinal Coulomb form factors and considered as an essential forexplanation the data amazingly throughout the whole range ofconsidered momentum transfer.

Toroidal Modes in Nuclei by Inelastic Electron Scattering

Electron scattering is a tool that can provide relatively clean view of the nuclear structure in both ground and excited states, as it depends on the well-known electromagnetic interaction. But since the common expressions for its cross section were derived with certain assumptions, in this paper we describe several nontrivial steps necessary for a proper theoretical calculation within the current density-functional framework, namely with Skyrme QRPA for axial nuclei, with aim to enable comparison of the theoretically predicted low-lying $1^-$ toroidal modes with future (e,e') experiments.

Bose-Einstein condensation of α clusters and new soft mode in C12 – Fe52 4N nuclei in a field-theoretical superfluid cluster model

Bose-Einstein condensation of alpha clusters in light and medium-heavy nuclei is studied in the frame of the field theoretical superfluid cluster model. The order parameter of the phase transition from the Wigner phase to the Nambu-Goldstone phase is a superfluid amplitude, square of the moduli of which is the superfluid density distribution. The zero mode operators due to the spontaneous symmetry breaking of the global phase in the finite number of alpha clusters are rigorously treated. The theory is systematically applied to N alpha nuclei from12C-52Fe at various condensation rates. In 12C it is found that the energy levels of the gas-like well-developed alpha cluster states above the Hoyle state are reproduced well in agreement with experiment for realistic condensation rates of alpha clusters. The electric E2 and E0 transitions are calculated and found to be sensitive to the condensation rates. The profound raison d'etre of the alpha cluster gas-like states above the Hoyle state, whose structure has been interpreted geometrically in the nuclear models without the order parameter such as the cluster models or ab initio calculations, is revealed. It is found that in addition to the Bogoliubov-de Gennes vibrational mode states collective states of the zero mode operators appear systematically at low excitation energies from the N alpha threshold energy. These collective states, new-type soft modes in nuclei due to the Bose-Einstein condensation of the alpha clusters, emerge systematically in light and medium-heavy mass regions and are also located at high excitation energies from the ground state in contrast to the traditional concept of soft mode in the low excitation energy region.

Nuclear surface energy coefficients in cluster decay

The influence of different nuclear surface energy coefficients of the proximity potential in cluster decay of heavy, unstable radioactive nuclei is studied using a fission model by incorporating the preformation probability as the penetration probability of the overlapping region. An expression for preformation probability is fitted for preformation values, for which best matching is noted between calculated and experimental half-lives and is used in further calculations of cluster decay of superheavy elements. Half-lives for heavy cluster emission such as Ar, Ca, Ti, Cr, Fe, Co, Ni, Zn, Ga, Ge and Se, from superheavy nuclei with mass number in the range $ 252 \leq A \leq 294$ are predicted using the fitted expression for preformation probability. Predicted half-lives of heavy particle decay of superheavy nuclei compare well with the other prediction for a few clusters. Alpha decay being the predominant decay mode of heavy and superheavy nuclei, half-lives of heavy and superheavy nuclei are also calculated. Calculated half-lives of alpha decay for superheavy nuclei better reproduce the experimental values.

Nanoparticle Emissions and GPF for MPI Gasoline Cars

Further efforts to reduce the air pollution from traffic are undertaken worldwide and the filtration of exhaust gas will also be increasingly applied on gasoline cars (GPF) … gasoline particle filter).In the present paper, some results of investigations of nanoparticles from four MPI gasoline cars are represented. The measurements were performed at vehicle tailpipe and in CVS-tunnel. Moreover, two variants of GPF were investigated on a high-emitting modern vehicle, including analytics of PAH and attempts of soot loading in road application.The modern MPI vehicles can emit a considerable amount of PN, which in some cases attains the level of Diesel exhaust gas without DPF and can pass over the actual European limit value for GDI (6.0 × 1011 #/km). The GPF-technology offers in this respect further potentials to reduce the PN-emissions of traffic. With GPF, in the investigated steady state operation, there is no significant visible nuclei mode and the ultrafine particles concentrations below 10 nm size are insignificant.