Dinuclear System Research Articles

Possibilities for synthesis of new isotopes of superheavy nuclei in cold fusion reactions

In order to find a way to produce superheavy nuclei (SHN), which appear in the gap between the SHN synthesized by cold fusion and those by hot fusion, or those so far not yet been produced in the laboratory, we tried to make use of a set of projectile isotopic chains, to use a radioactive beam projectile, and to test symmetric fusion reactions for gaining more neutrons to synthesize neutron-richer SHN based on the dinuclear system (DNS) model via cold fusion reactions. It is found that the nuclei (265)Mt, (268,272)Ds, (273)Rg, and (274,275,276)Cn may be produced with the detectable evaporation residual cross sections. The intensities of radioactive beams are significantly less than those of the stable beams, therefore using a stable beam is predicted to be the most favorable method for producing SHN. From the symmetric reaction system Xe-136 + Xe-136, no fusion event was found.

Ligand Attachment Chemistry in the Preparation of PCsp3P and PCsp2P Complexes of Rhodium

The attachment of electron-rich PCP pincer ligands bis(2-(dialkylphosphino)phenyl)methane (alkyl = isopropyl, tert-butyl) to rhodium via reactions with [(COE)2Rh(μ-X)]2 (X = Cl, OSO2CF3) through C–H bond activations is reported. The first C–H activation to produce PCsp3P derivatives is facile and favors products wherein the remaining benzylic C–H and the Rh–H hydrogens are trans-disposed across the new Rh–C bond. For the less bulky isopropyl-substituted ligand, chlorido- or triflato-bridged dinuclear products are favored, while for the tert-butyl-adorned ligand, monomers are formed. The favoring of both trans C–H/Rh–H and dinuclear systems hampers the second C–H activation, necessary to form the (more desirable) PCcarbeneP derivatives. Through spectroscopic and structural investigations, the factors that influence the ligand attachment chemistry through successive C–H activations in these ligands are discussed.

Interpretation of the low energy fission process in the framework of dinuclear system conception

The possibility of the interpretation of fission of heavy nuclei as the process of formation, evolution and decay of dinuclear system is discussed. The interpretation is based on the nuclear interaction data obtained in heavy-ion nuclear physics investigations.

Description of alpha decay and cluster radioactivity in the dinuclear system model

A unified description of cluster radioactivity and α-decay of cold nuclei in the dinuclear system model is proposed. Quantum dynamical fluctuations along the charge (mass) asymmetry coordinate determine the spectroscopic factor, and tunneling along the relative distance coordinate determines the penetrability of the barrier of the nucleus–nucleus interaction potential. A new method for calculating the spectroscopic factor is proposed. The hindrance factors for the orbital angular momentum transfer are studied. A potential reason for the half-life to deviate from the Geiger–Nuttall law in α-decays of neutron-deficient nuclei 194, 196Rn is found. The fine structure of α-decays of U and Th isotopes is predicted and characterized. The model is used to describe α-decays from the rotational band of even–even nuclei. The known half-lives in the regions of “lead” and “tin” radioactivities are reproduced well, and the most probable cluster yields are predicted. The cluster decay of excited nuclei is discussed. The relation of cluster radioactivity to spontaneous fission and highly deformed nuclear states is analyzed.

Quasifission and fusion-fission processes in the reactionsKr78+Ca40andKr86+Ca48at 10 MeV/nucleon bombarding energy

Within the dinuclear system model the charge, mass, and isotopic distributions of the products in the reactions $^{78}\mathrm{Kr}+^{40}\mathrm{Ca}$ and $^{86}\mathrm{Kr}+^{48}\mathrm{Ca}$ are predicted at bombarding energy 10 MeV/nucleon. The heavy-ion phase-space exploration code is applied to take into consideration the pre-equilibrium emission of light particles. The competition is treated between complete fusion followed by the decay of compound nucleus and quasifission channels. The possible explanation of the odd-even staggering in the yield of the final reaction products at high excitation energies is discussed.

Multinucleon transfer in theXe136+Pb208reaction

The dynamic mechanics in the multinucleon transfer reaction $^{136}\mathrm{Xe}+^{208}\mathrm{Pb}$ at an incident energy of ${E}_{\mathrm{c}.\mathrm{m}.}=450$ MeV is investigated by using the improved quantum molecular dynamics model (ImQMD). The lifetime of the neck directly influences the nucleon exchange and energy dissipation between the projectile and the target. The total-kinetic-energy--mass distributions and excitation energy division of primary binary fragments and the mass distributions of primary fragments at different impact parameters are calculated. The thermal equilibrium between two reaction partners has been observed at the lifetime of a neck larger than $480\phantom{\rule{4.pt}{0ex}}\mathrm{fm}/c$. By using the statistical decay code gemini to describe the de-excitation process of the primary fragments, the isotope production cross sections from Pt to At are compared with the prediction by the dinuclear system and GRAZING model. The calculations indicate that the GRAZING model is suitable for estimating the isotope production cross sections only for $\mathrm{\ensuremath{\Delta}}Z=\ensuremath{-}1$ to +2; the DNS + gemini calculations underestimate the cross sections in the neutron-rich and neutron-deficient regions; and the ImQMD + gemini calculations give reasonable predictions of the isotope production cross sections for $\mathrm{\ensuremath{\Delta}}Z=\ensuremath{-}3$ to 0.

Description of the Fusion-Fission Reactions in the Framework of Dinuclear System Conception

Within the dinuclear system model fusion-fission reactions 78Kr+40Ca and 86Kr+48Ca is investigated. The charge distributions of the decay products are predicted at bombarding energy 10 MeV/nucleon. The competition is treated between complete fusion followed by the decay of compound nucleus and quasifission channels. The possible explanation of the odd-even staggering in the yield of the final reaction products at high excitation energies is discussed.

Description of quasifission reactions in the dinuclear system model

The formation and evolution of dinuclear systems in quasifission reactions are investigated. The process of formation of reaction products is analyzed based on the concept of a dinuclear system. Isotopic trends of cross sections of production of superheavy nuclei in quasifission reactions are discussed. The yields of new neutron-rich isotopes of nuclei with Z = 64–80 in quasifission reactions are predicted. The mechanism of production of complex fragments in complete fusion and quasifission reactions is analyzed.

Effect of entrance channel on dynamics of heavy ions collision

A combined dynamical model using concept of dinuclear systems (DNS) and one-dimensional (1D) Langevin equations was applied to investigate the effect of entrance channel on dynamics of heavy ions collision. The [Formula: see text]Si+[Formula: see text]Er, [Formula: see text]O+[Formula: see text]W and [Formula: see text]F+[Formula: see text]Ta reactions which formed the compound nucleus [Formula: see text]Pb have been considered to study this effect. We studied these reactions dynamically and calculated the ratio of evaporation residue cross-section to fusion cross-section [Formula: see text] as a tool for investigation of entrance channel effect. Results of combined model are compared with available experimental data and results of 1D Langevin equations. Obtained results based on combined model are in better agreement with experimental data in comparison with results of Langevin equations. We concluded for [Formula: see text]Si+[Formula: see text]Er and [Formula: see text]F+[Formula: see text]Ta reactions the results of combined model that support the quasi-fission process are different relative to Langevin dynamical approach, whereas for [Formula: see text]O+[Formula: see text]W system the two models give similar results.

Nuclear structure effects in quasifission – understanding the formation of the heaviest elements

Quasifission is an important process suppressing the fusion of two heavy nuclei in reactions used to create superheavy elements. Quasifission results in rapid separation of the dinuclear system initially formed at contact. Achieving reliable a priori prediction of quasifission probabilities is a very diffcult problem. Through measurements with projectiles from C to Ni, the Australian National University’s Heavy Ion Accelerator Facility and CUBE spectrometer have been used to map out mass-angle distributions (MAD) - the fission mass-ratio as a function of centre-of-mass angle. These provide information on quasifission dynamics in the least modeldependent way. Average quasifission time-scales have been extracted, and compared with TDHF calculations of the collisions, with good agreement being found. With the baseline information from the survey of experimental MAD, strong influences of the nuclear structure of the projectile and target nuclei can be clearly determined.

Application of the dinuclear system model to fission process

A theoretical evaluation of the collective excitation spectra of nucleus at large deformations is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of nucleons between clusters. In this work the method of calculation of the potential energy and the collective spectrum of fissioning nucleus at scission point is presented. Combining the DNS model calculations and the statistical model of fission we calculate the mass, total kinetic energy, and angular distribution of fission fragments for the neutron–induced fission of 239 Pu.

Peculiarities of quasifission reactions in heavy ion collisions

The probability of the formation and decay of a dinuclear system is investigated for a wide range of relative orbital angular momentum values. The mass and angular distributions of the quasifission fragments are studied to understand the reaction mechanisms of the heavy ion collision of 78Kr (10A MeV) + 40Ca within dinuclear system model. The quasifission products are found to contribute to the mass-symmetric region of the mass distribution in collisions with a large orbital angular momentum. The analysis of mass and angular distributions of quasifission fragments shows the possibility of the 180° rotation of the system so that projectile-like products can be observed in the forward hemisphere with large cross sections, which can explain the phenomenon observed recently in the ISODEC experiment.

Rigid linked dinuclear salph-co(III) catalyst for carbondioxide/epoxides copolymerization

Mononuclear and dinuclear salen-co(III) catalysts were designed for carbon dioxide (CO2) and propylene oxide (PO) copolymerization. The dinuclear system maintained its activity with a turn over frequency (TOF) of 406h−1 at [PO]/[Cat]=20,000. In contrast, the mononuclear catalyst system almost lost its activity with a TOF of 3h−1. The two cobalt centers in dinuclear structure may work synergistically due to the conjugated structure. This may contribute to the enhancement of the activity. The dinuclear catalyst system offered the highest molecular weight (Mn=200,000) among reported dinuclear catalysts heretofore. Polymerization mechanism for the dinuclear catalyst system was postulated based on the subtly designed experiments. Synergy effect with the positive help of cocatalyst was explored. To further enhanced the thermal property of poly(propylene carbonate) (PPC), poly(cyclohexene carbonate) (PCHC) was incorporated. The glass transformation temperature of the copolymer of PPC-PCHC could be adjusted by the feed ratio of PO and cyclohexene oxide (CHO).

Isotopic dependence of superheavy nuclear production in hot fusion reactions

The dependence of the evaporation residue cross section (ERCS)'s ability to produce superheavy nuclei (SHN) on the isospin of colliding nuclei is analyzed within the dinuclear system concept. ERCSs are discussed in detail and compared with existing experimental data. The fusion probabilities and surviving probabilities depend sensitively on the neutron numbers of the target and projectile nuclei. In most cases a neutron excess in the system can increase the producing cross section of a new nuclide of SHN. Some predicted ERCSs for the new isotopes of SHN were found to be as large as about 1--8 pb, which is large enough to be realized experimentally with the current existing technology. Element 120 may be produced by $^{50}\mathrm{Ti}+^{251,252}\mathrm{Cf}$, with the ERCS being about 0.03 pb, and element 119 may be produced by the reaction channel $^{50}\mathrm{Ti}+^{248,249}\mathrm{Bk}$, with the ERCS being about 0.1 pb via $3n$ and $4n$ emission channels, respectively. Radioactive projectiles are not much more favorable in comparison to stable projectiles.

Cluster approach to the structure ofPu240

The cluster approach, which allows us to take into account both shape deformation parameters and cluster degrees of freedom, is developed to describe alternating-parity rotational bands. The important ingredient of the model is the dinuclear system concept in which the wave function of the nucleus is treated as a superposition of a mononucleus and two-cluster configurations. The model is applied to describe the multiple positive and negative parity rotational bands in $^{240}\mathrm{Pu}$. The observed excitation spectrum and the angular momentum dependences of the parity splitting and of the electric $E1$ and $E2$ transition moments are explained. Special emphasis is made on the investigation of the recently measured positive parity ${0}_{2}^{+}$ rotational band of reflection-asymmetric nature. The results suggest that this band might be understood as being built on the lowest excited state in the mass asymmetry degree of freedom. The $B(E1)/B(E2)$ branching ratios between the reduced transition probabilities of decay from the states of the ${0}_{2}^{+}$ band to the first negative parity band and to the groundstate band, respectively, are calculated and compared with experimental data.

Universal damping mechanism of quantum vibrations in deep sub-barrier fusion reactions

We demonstrate the damping of quantum octupole vibrations near the touching point when two colliding nuclei approach each other in the mass-asymmetric $^{208}$Pb + $^{16}$O system, for which the strong fusion hindrance was clearly observed. We, for the first time, apply the random-phase approximation method to the heavy-mass asymmetric di-nuclear system to calculate the transition strength $B$(E3) as a function of the center-of-mass distance. The obtained $B$(E3) strengths are substantially damped near the touching point, because the single-particle wave functions of the two nuclei strongly mix with each other and a neck is formed. The energy-weighted sums of $B$(E3) are also strongly correlated with the damping factor which is phenomenologically introduced in the standard coupled-channel calculations to reproduce the fusion hindrance. This strongly indicates that the damping of the quantum vibrations universally occurs in the deep sub-barrier fusion reactions.

Fusion–fission dynamics studies using mass distribution as a probe

Study of quasifission reaction mechanism and shell effects in compound nuclei has important implications on the synthesis of superheavy elements (SHE). Using the major accelerator facilities available in India, quasifission reaction mechanism and shell effects in compound nuclei were studied extensively. Fission fragment mass distribution was used as a probe. Two factors, viz., nuclear orientation and direction of mass flow of the initial dinuclear system after capture were seen to determine the extent of quasifission. From the measurement of fragment mass distribution in α-induced reaction on actinide targets, it was possible to constrain the excitation energy at which nuclear shell effect washed out.

Approximating the spin distributions in capture reactions between spherical nuclei

Twenty years ago an approximation for the spin distribution of the dinuclear systems formed in capture reactions with heavy ions was proposed. This approximation is used nowadays. However, since that time the experimental errors of the measured capture cross sections were reduced drastically. We show that the accuracy of the old spin distribution approximation is certainly out of date and propose a new approximation built on the dynamical modeling of the capture process. Results suggest that this new approximation might be useful especially for performing modeling of decay of excited dinuclear systems (compound nuclei) formed during heavy-ion collisions.

Copper(II) complexes of terminally free alloferon peptide mutants containing two different histidyl (H1 and H6 or H9 or H12) binding sites Structure Stability and Biological Activity

Mono- and dinuclear copper(II) complexes of the alloferon 1 with point mutations H9A/H12A H1GVSGH6GQA9GVA12G, H6A/H12A H1GVSGA6GQH9GVA12G and H6A/H9A H1GVSGA6GQA9GVH12G have been studied by potentiometric, UV-visible, CD, EPR spectroscopic, and mass spectrometry (MS) methods. Complete complex speciation at metal-to-ligand molar ratios 1:1 and 2:1 was obtained. For all systems studied in the 5 – 6.5 pH range, the CuL complex dominates with 3N{NH2,NIm-H1,NIm-H6 or 9 or 12} binding site. The stability of the CuL complexes for the ligands studied varies according to the H9A/H12A>H6A/H12A>H6A/H9A series. For the dinuclear systems the amine/imidazole nitrogen donor atoms of the histidine residue H1 and the imidazole nitrogen atoms of H6 or H9 or H12 can be considered as independent metal-binding sites in the species formed. The stability of the dinuclear complexes is higher when two coordinated copper(II) ions are closer to each other.The inductions of phenoloxidase activity and apoptosis in vivo in Tenebrio molitor cells by the ligands and their copper(II) complexes at pH7.4 have been studied. The H6A/H9A, H6A/H12A peptides displayed lower hemocytotoxic activity compared to that of alloferon 1, while the H9A/H12A analogue was not active. Among the copper(II) complexes, the most active was the Cu(II)-H9A/H12A complex formed at pH7.4 with 3N{NH2,NIm-H1,NIm-H6} (CuL) and 3N{NH2,N−,NIm-H6} and/or 4N{NH2,NIm-H1,N−,NIm-H6} (CuH−1L) binding sites. The Cu(II)-H6A/H9A and Cu(II)-H6A/H12A complexes were not active.

Influence of nuclear basic data on the calculation of production cross sections of superheavy nuclei

The center of the predicted island of stability of superheavy nuclei (SHN) has not yet been observed experimentally. Many theories are being developed to understand the synthesizing mechanism of superheavy nuclei. However, all of them have to use some basic nuclear data. Three data tables, FRDM1995 [P. M\oller et al., At. Data Nucl. Data Tables 59, 185 (1995)], KTUY2005 [H. Koura et al., Prog. Theor. Phys. 113, 305 (2005)], and WS2010 [Ning Wang et al., Phys. Rev. C 82, 044304 (2010)], are used to investigate the SHN production. Based on the dinuclear system concept, the evaporation residue cross sections of SHN for $Z$=112--118 are calculated for the $^{48}\mathrm{Ca}$-induced hot fusion reactions. It turns out that unlike the predictions made with the KTUY2005 and WS2010 data, the magic numbers $Z$=114 and $N$=184 predicted with the FRDM1995 data do not contradict the experimental data obtained so far.