Transactinide Nuclei Research Articles

Peculiarities of Rotational Bands in Heavy and Superheavy Nuclei: Description of Yrast-Band States in 248Cm

A further development of the expanded microscopic version of the IBM is presented by considering two-quasiparticle phonons with multipolarity up to J = 14+J. The developed theoretical scheme is applied to describe the properties of the yrast-band states in 248Cm up to spin 34+. This heavy transactinide nucleus is the only nucleus in this mass region where the values of B(E2) up to spin I = 28+ are measured. That is why it is considered foremost, because this information allows testing the presented theoretical scheme based on a larger volume of experimental data. The region of transactinide nuclei differs from lighter ones by the absence of the effect of the back bending in the moment of inertia dependence on the square of the rotation frequency up to the spin I = 28+. This article is intended in particular to find out the reason for this effect. Peculiar properties of the rotational bands in heavy and superheavy nuclei are discussed.

Prediction of high-K isomeric states in transactinide nuclei close to N=162

Transactinide nuclei around neutron number N=162 display axially deformed equilibrium shapes. In the present study we are particularly interested in the occurrence of high-K isomers in the axially deformed isotopes of Rf (Z=104), Sg (Z=106), Hs (Z=108), and Ds (Z=110), with neutron number N=160-166 and the effect of the N=162 closure on the structure and distribution of two-quasiparticle (2qp) states. The evolution of high-K isomers is analyzed in a self-consistent axially symmetric relativistic Hartree-Bogoliubov calculation using the blocking approximation with time-reversal symmetry breaking.

Spontaneous fission and competing ground state decay modes of actinide and transactinide nuclei

Based on the preformed cluster model, we have carried out a comprehensive theoretical study on the decay paths of ground state actinide and transactinide nuclei, specifically from $^{232}\mathrm{U}$ to $^{264}\mathrm{Hs}$ exhibiting the phenomenon of spontaneous fission (SF). This is an extension of our earlier studies on $\ensuremath{\alpha}$ decay, exotic cluster emission, and heavy particle radioactivity, where an effort is made to identify the most probable fragments in the SF process. These observations in turn, could provide a testing ground for future SF half-life measurements. To obtain a clear picture of the dynamics involved, the variations of fragmentation potential, preformation factor, and decay barrier height have been examined. The calculated potential energy surfaces show a change from a predominantly asymmetric fission to a symmetric fragmentation with the increase in the N/Z ratio of parent nuclei. In addition, an exclusive analysis of SF with $\ensuremath{\alpha}$ and other possible cluster emissions for the $^{232,234,236,238}\mathrm{U}$ parents was made to have better insight of nuclear structure information. In other words, the comparative nature of $\ensuremath{\alpha}$, cluster, heavy fragment, and SF decay paths is analyzed in view of shell closure property of the decay fragments. Interestingly, the calculated decay half-lives for the $^{82}\mathrm{Ge}$ heavy cluster are in fact shown to lie within the limits of experiments, thereby presenting themselves as exciting new possibilities which may be validated via future experiments.

Decay analysis of pre-actinide and trans-actinide nuclei formed using various projectiles on aAu197target atECN*=60MeV

Decay analysis of pre-actinide and trans-actinide nuclei formed using various projectiles on a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mtext>Au</mml:mtext><mml:mprescripts /><mml:none /><mml:mn>197</mml:mn></mml:mmultiscripts></mml:math>target at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>E</mml:mi><mml:mrow><mml:mi>CN</mml:mi></mml:mrow><mml:mo>*</mml:mo></mml:msubsup><mml:mo>=</mml:mo><mml:mn>60</mml:mn></mml:mrow></mml:math>MeV

On spontaneous fission and α-decay half-lives of atomic nuclei

It is shown, that the Gamow-like model with only one adjustable parameter–radius constant—is able to reproduce well the alpha-decay half-lives for all even–even nuclei with the proton number larger than 50. The systematics for odd–A and odd–odd isotopes can be also well described when one introduces an additional hindrance factor. A similar model based on the W J Świa̧tecki idea from 1955 is developed to reproduce the spontaneous fission half-lives of transactinide nuclei. The achieved accuracy of reproduction of the data is better than that obtained in more advanced theories.

Consistent description of the cluster-decay phenomenon in transactinide nuclei

Systematic investigation of the known even-even transactinide cluster emitters has been carried out by considering the cluster as a point particle and using the exact quantum mechanical treatment of the decay process. It is shown that the cluster decay phenomenon can be described reasonably well using a simple Woods-Saxon mean field. Sensitivity of the half-lives on various aspects of the mean field has been investigated in detail.

Predicting the production of neutron-rich heavy nuclei in multinucleon transfer reactions using a semi-classical model including evaporation and fission competition, GRAZING-F

Background: Multi-nucleon transfer reactions have recently attracted attention as a possible path to the synthesis of new neutron-rich heavy nuclei. Purpose: We study transfer reactions involving massive nuclei with the intention of understanding if the semi-classical model GRAZING coupled to an evaporation and fission competition model can satisfactory reproduce experimental data on transfer reactions in which fission plays a role. Methods: We have taken the computer code GRAZING and have added fission competition to it (GRAZING-F) using our current understanding of $\Gamma_n/\Gamma_f$, fission barriers and level densities. Results: The code GRAZING-F seems to satisfactory reproduce experimental data for $+1p$, $+2p$ and $+3p$ transfers, but has limitations in reproducing measurements of larger above-target and below-target transfers. Nonetheless, we use GRAZING-F to estimate production rates of neutron-rich $N=126$ nuclei, actinides and transactinides. Conclusions: The GRAZING code, with appropriate modifications to account for fission decay as well as neutron emission by excited primary fragments, does not predict large cross sections for multi-nucleon transfer reactions leading to neutron-rich transactinide nuclei, but predicts opportunities to produce new neutron-rich actinide isotopes.

High-Kisomers in transactinide nuclei close toN=162

We extend our recent study of shape evolution, collective excitation spectra, and decay properties of transactinide nuclei [V. Prassa, T. Nik\ifmmode \check{s}\else \v{s}\fi{}i\ifmmode \acute{c}\else \'{c}\fi{}, and D. Vretenar, Phys. Rev. C 88, 044324 (2013)], based on the microscopic framework of relativistic energy density functionals, to two-quasiparticle (2qp) excitations in the axially deformed Rf, Sg, Hs, and Ds isotopes, with neutron number $N=160--166$. The evolution of high-$K$ isomers is analyzed in a self-consistent axially symmetric relativistic Hartree-Bogoliubov calculation using the blocking approximation with time-reversal symmetry breaking. The occurrence of a series of low-energy high-$K$ isomers is predicted, in particular the ${9}_{\ensuremath{\nu}}^{\ensuremath{-}}$ in the $N=160$ and $N=166$ isotopes, and the ${12}_{\ensuremath{\nu}}^{\ensuremath{-}}$ in the $N=164$ nuclei. The effect of the $N=162$ deformed-shell closure on the excitation of 2qp states is discussed. In the $N=162$ isotones we find a relatively low density of 2qp states, with no two-neutron states below 1.6 MeV excitation energy and two-proton states at $\ensuremath{\approx}0.5$ MeV higher energy than the lowest 2qp states in neighboring isotopes. This is an interesting result that can be used to characterise the occurrence of deformed shell gaps in very heavy nuclei.

Structure of transactinide nuclei with relativistic energy density functionals

A microscopic theoretical framework based on relativistic energy density functionals (REDFs) is applied to studies of shape evolution, excitation spectra, and decay properties of transactinide nuclei. Axially symmetric and triaxial relativistic Hartree-Bogoliubov (RHB) calculations, based on the functional DD-PC1 and with a separable pairing interaction, are performed for the even-even isotopic chains between Fm and Fl. The occurrence of a deformed shell gap at neutron number $N=162$ and its role on the stability of nuclei in the region around $Z=108$ is investigated. A quadrupole collective Hamiltonian, with parameters determined by self-consistent constrained triaxial RHB calculations, is used to examine low-energy spectra of No, Rf, Sg, Hs, and Ds with neutron number in the interval $158\ensuremath{\le}N\ensuremath{\le}170$. In particular, we analyze the isotopic dependence of several observables that characterize the transitions between axially symmetric rotors, $\ensuremath{\gamma}$-soft rotors, and spherical vibrators. An interesting example of a possible occurrence of shape-phase transitions and critical-point phenomena in this mass region is explored.

New nuclear structure features in transactinide nuclei

The structural evolution of heavy nuclei, with $Z&gt;82$, is investigated by looking at the differential variation of the two-neutron separation energies. It indicates, by nonmonotonous behavior at certain neutron numbers, structure phenomena such as major shell ($N=126$) and deformed subshell ($N=152$) closures. Another interesting effect is observed at $N\ensuremath{\sim}142$, which is very well correlated with a previously observed, intriguing behavior of quantities measured in $\ensuremath{\alpha}$ decay, such as relative branching ratios and hindrance factors of excited states from the ground-state band of deformed nuclei in this region. Corroboration of the existing experimental data indicates another possible deformed subshell closure.

Structure of superheavy nuclei

Properties of transactinide nuclei needed for the interpretation of spectroscopic data and for the extrapolation to the expected "island of stability" of superheavy nuclei are reviewed from a theorist's point of view in the framework of self-consistent mean-field models.

Rotational states and masses of heavy and superheavy nuclei

The macroscopic-microscopic model with the Lublin-Strasbourg drop, the Strutinsky shell-correction method, and the BCS approach for pairing correlations is used with the cranking model to describe nuclear masses and rotational bands in even-even Ra to Cn isotopes of actinide and transactinide nuclei. The single-particle levels and potential-energy surfaces are calculated with the Yukawa-folded single-particle potential using the “modified funny hills” (c, h) shape parametrization. A monopole pairing force is used in our calculations. At equilibrium deformation the pairing strength is adjusted for every nucleus so as to reproduce the experimentally known rotational E2+ state within the cranking model. The pairing strength obtained in this way is used to predict the masses and rotational states in superheavy No to Cn nuclei. It is also shown that the rotational states with L 10 in Ra to No nuclei evaluated using a simple rotational formula agree quite well with the data. We propose a simple mechanism which takes into account a dynamical coupling of rotation with the pairing field that then allows one to obtain an excellent agreement with the data up to the states with the largest angular momenta (L 30) measured in this mass region.

Nuclear spectroscopy of the heaviest elements: studies of 254No, 257Rf, and 261Sg

Recently it has become possible to perform detailed spectroscopy on nuclei beyond Z = 100 with the aim of understanding the underlying single-particle structure of superheavy elements. A number of such experiments have been performed at the 88-Inch Cyclotron of the Lawrence Berkeley National Laboratory using the Berkeley Gas-filled Separator (BGS), coupled with delayed γ-ray and electron-decay spectroscopy. Experiments have been performed on 254No (Z = 102), 257Rf (Z = 104), and 261Sg (Z = 106). The results provide new information on the properties of transactinide nuclei, which is important for testing models of the heaviest elements.

Spectroscopy of actinide and transactinide nuclei

Abstract The role of isomers for nuclei with Z ≥ 100 is discussed. Recent advances in experimental instrumentation leading to combined in-beam gamma ray and conversion electron spectroscopy are discussed. The rotational spectra of nuclei with Z ≥ 94 and their moments of inertia are discussed. Examples for in-beam spectroscopy leading to the discovery and identification of isomers are given in 248,250Fm. Here some attention is given to the assignment of nuclear configurations from g-factors measured via the branching ratios of coupled bands built on the isomers. A full list of the longest lived isomers in nuclei with Z ≥ 82 is given.

Synthesis of transactinide nuclei in cold fusion reactions using radioactive beams

Chances of synthesis of transactinide nuclei in cold fusion reactions (one-neutron-out reactions) using radioactive beams are evaluated. Because in most of the cases intensities of radioactive beams are significantly less than those of the stable beams, reactions with the greatest radioactive-beam intensities for the particular elements are considered. The results are compared with the recent ones obtained by Loveland [Phys. Rev. C 76, 014612 (2007)], who investigated the same nuclei.

CLUSTERING PHENOMENA IN SUPERHEAVY NUCLEAR SYSTEMS

Dynamics of heavy-ion low energy damped collisions is studied within the model based on the Langevin type equations. Shell effects on the multi-dimensional potential energy surface play an important role in these reactions. This leads to several local minima on the fission path of heavy nucleus — so called isomeric states which are nothing else but the two-cluster configurations with magic or semi-magic cores surrounded with a certain number of shared nucleons. In a giant nuclear system (formed, for example, in U + U collision) the three-body clustering configurations may also appear. Enhanced yield of the nuclides far from the projectile and target masses was found in the multi-nucleon transfer reactions due to the shell effects. It suggests that the low-energy damped collisions of transactinide nuclei may be used as an alternative way for the production of surviving superheavy long-living neutron-rich nuclei.

Observation of the3nEvaporation Channel in the Complete Hot-Fusion ReactionMg26+Cm248Leading to the New Superheavy NuclideHs271

The analysis of a large body of heavy ion fusion reaction data with medium-heavy projectiles (6 < or = Z < or = 18) and actinide targets suggests a disappearance of the 3n exit channel with increasing atomic number of the projectile. Here, we report a measurement of the excitation function of the reaction (248)Cm ((26)Mg,xn)(274-x)Hs and the observation of the new nuclide (271)Hs produced in the 3n evaporation channel at a beam energy well below the Bass fusion barrier with a cross section comparable to the maxima of the 4n and 5n channels. This indicates the possible discovery of new neutron-rich transactinide nuclei using relatively light heavy ion beams of the most neutron-rich stable isotopes and actinide targets.

COLLECTIVE EXCITATIONS OF TRANSACTINIDE NUCLEI IN A SELF-CONSISTENT MEAN FIELD THEORY

We applied the ATDHFB approach for study of properties of collective quadrupole states in several transactinide nuclei: 238 U , 240 Pu , 242 Pu , 246 Cm , 248 Cm , 250 Cf and 252 Cf . Calculated energies and B(E2) transition probabilities are in a reasonable agreement with experimental data. We present also results concerning superdeformed collective states in the second minimum of potential energy of the 240 Pu nucleus.

Synthesis of transactinide nuclei using radioactive beams

The prospects for the synthesis of transactinide nuclei using radioactive beams are evaluated quantitatively for a modern radioactive beam facility. A simple formalism for calculating the complete fusion cross sections that reproduces the known heavy element production cross sections over six orders of magnitude is used to calculate the production rates for transactinide nuclei with $Z\ensuremath{\leqslant}120$. All possible projectile and target combinations are evaluated. Exciting new possibilities for studies of the atomic physics, chemistry, and nuclear spectroscopy of the heaviest elements should be realized at a modern radioactive beam facility. The synthesis of new heavy elements is best undertaken at stable beam accelerators.

Superheavy nuclei and giant quasi-atoms

Dynamics of heavy-ion low energy collisions is studied within the realistic model based on multi-dimensional Langevin equations. Symmetric and asymmetric fusion reactions leading to formation of superheavy nuclei are analyzed. Collisions of transactinide nuclei are investigated as an alternative way for production of neutron-rich superheavy elements. In many events lifetime of the composite giant system consisting of two touching nuclei turns out to be rather long ( ⩾ 10 −20 s ); sufficient for observing line structure in spontaneous positron emission from super-strong electric fields, a fundamental QED process.