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The new MUSETT silicon-wall has been built to study and obtain detailed spectroscopic information on the transfermium and transactinide elements. MUSETT is located at GANIL at the detection plane of VAMOS, the latter coupled with the EXOGAM germanium array. Results from the in-beam commissioning are reported and an overview of our future experimental program will be given.
Experiments were performed at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron facility to investigate the electron-transfer reduction reaction of dipositive Lr ( Z = 103) with O 2 gas. Ions of 255 Lr were produced in the fusion-evaporation reaction 209 Bi( 48 Ca,2n) 255 Lr and were studied with a novel gas-phase ion chemistry technique. The produced 255 Lr 2+ ions were trapped and O 2 gas was introduced, such that the charge-exchange reaction to reduce 255 Lr 2+ to 255 Lr 1+ was observed and the reaction rate constant was determined to be k = 1.5(7) × 10 -10 cm 3 /mol/s. The observation that this reaction proceeds establishes the lower limit on the second ionization potential of Lr to be 13.3(3) eV. This gives further support that the actinide series terminates with Lr. Additionally, this result can be used to better interpret the situation concerning the placement of Lu and Lr on the periodic table within the current framework of the actinide hypothesis. The success of this experimental approach now identifies unique opportunities for future gas-phase reaction studies on actinide and super heavy elements.
We report the formulation and implementation of KRCASPT2, a two-component multi-configurational second-order perturbation theory based on Kramers restricted complete active space self-consistent field (KRCASSCF) reference function, in the framework of the spin-orbit relativistic effective core potential. The zeroth-order Hamiltonian is defined as the sum of nondiagonal one-electron operators with generalized two-component Fock matrix elements as scalar factors. The Kramers symmetry within the zeroth-order Hamiltonian is maintained via the use of a state-averaged density, allowing a consistent treatment of degenerate states. The explicit expressions are derived for the matrix elements of the zeroth-order Hamiltonian as well as for the perturbation vector. The use of a fully variational reference function and nondiagonal operators in relativistic multi-configurational perturbation theory is reported for the first time. A series of initial calculations are performed on the ionization potential and excitation energies of the atoms of the 6p-block; the results display a significant improvement over those from KRCASSCF, showing a closer agreement with experimental results. Accurate atomic properties of the superheavy elements of the 7p-block are also presented, and the electronic structures of the low-lying excited states are compared with those of their lighter homologues.
A formula for the relationship between the {alpha}-decay energies (Q values) of superheavy nuclei (SHN) is presented, which is composed of the effects of Coulomb energy and symmetry energy. It can be employed not only to validate the experimental observations and measurements to a large extent, but also to predict the Q values of heaviest SHN with a high accuracy generally which will be very useful for future experiments. Furthermore, the shell closures in superheavy region and the effect of the symmetry energy on the stability of SHN against {alpha} decay are discussed with the help of this formula.
Studies of the chemical properties of superheavy elements (SHE) pose interesting challenges due to their short half-lives and low production rates. Chemical systems must have extremely fast kinetics, fast enough kinetics to be able to examine the chemical properties of interest before the SHE decays to another nuclide. To achieve chemistry on such time scales, the chemical system must also be easily automated. Most importantly however, a chemical system must be developed which provides suitable separation and kinetics before an on-line study of a SHE can be performed. Relativistic effects make studying the chemical properties of SHEs interesting due to the impact these effects could have on the SHEs chemical properties. Relativistic effects arise when the velocity of the s orbital electrons approach the speed of light. As this velocity increases, the Bohr radius of the inner electron orbitals decreases and there is an increase in the particles mass. This contraction results in a destabilization of the energy of the outer d and f electron orbitals (5f and 6d in the case of SHE), which can cause these to expand due to their increased shielding from the nuclear charge. Another relativistic effect is the spin-orbit splitting for p, d, and f orbitals into j = 1 1/2 states. This can lead most interestingly to a possible increased stability of element 114, which due to large spin-orbit splitting of the 7p orbital and the relativistically stabilized 7p 1/2 and 7s orbital gives rise to a closed shell ground state of 7s 2 7p 1/2 2 . The homologs of element 105, dubnium (Db), Ta and Nb and the pseudo-homolog Pa, are well known to hydrolyze and form both neutral and non-neutral monoatomic and polyatomic species that may cause issues with extraction from a given chemical system. Early ion-exchange and solvent-extraction studies show mixed results for the behavior of Db. Some studies show Db behaving most similar to Ta, while others show it behaving somewhere between Nb and Pa. Much more recent studies have examined the properties of Db from HNO 3 /HF matrices, and suggest Db forms complexes similar to those of Pa. Very little experimental work into the behavior of element 114 has been performed. Thermochromatography experiments of three atoms of element 114 indicate that the element 114 is at least as volatile as Hg, At, and element 112. Lead was shown to deposit on gold at temperatures about 1000 C higher than the atoms of element 114. Results indicate a substantially increased stability of element 114. No liquid phase studies of element 114 or its homologs (Pb, Sn, Ge) or pseudo-homologs (Hg, Cd) have been performed. Theoretical predictions indicate that element 114 is should have a much more stable +2 oxidation state and neutral state than Pb, which would result in element 114 being less reactive and less metallic than Pb. The relativistic effects on the 7p 1/2 electrons are predicted to cause a diagonal relationship to be introduced into the periodic table. Therefore, 114 2+ is expected to behave as if it were somewhere between Hg 2+ , Cd 2+ , and Pb 2+ . In this work two commercially available extraction chromatography resins are evaluated, one for the separation of Db homologs and pseudo?homologs from each other as well as from potential interfering elements such as Group IV Rf homologs and actinides, and the other for separation of element 114 homologs. One resin, Eichrom's DGA resin, contains a N,N,N',N'-tetra-n-octyldiglycolamide extractant, which separates analytes based on both size and charge characteristics of the solvated metal species, coated on an inert support. The DGA resin was examined for Db chemical systems, and shows a high degree of selectivity for tri-, tetra-, and hexavalent metal ions in multiple acid matrices with fast kinetics. The other resin, Eichrom's Pb resin, contains a di-t-butylcyclohexano 18-crown-6 extractant with isodecanol solvent, which separates analytes based on steric interactions between the cavity of the crown ether and electrostatic interactions between the oxygen's of the ether and cations in the mobile phase. This particular resin has been shown to have an extremely high uptake affinity for Pb, a direct homolog of element 114, and is thus a good initial extractant to examine for a potential element 114 chemical system. Figure 1.1 shows the respective extractant molecules from the DGA and Pb resins. Batch uptake experiments were conducted to examine the uptake behavior of Ta on the DGA resin. Batch uptake experiments were also conducted to examine the uptake behavior of Ge on the Pb resin. Column experiments were designed based on batch uptake experiments of Ta, Am, Pa, Np, Zr, and Nb to establish a sequential extraction of Group IV/V homologs as well as Am for potential use as a Db chemical system.
The evaporation residue (ER) cross sections for 3n and 4n evaporation channels in the {sup 50}Ti + {sup 249}Bk reaction leading the formation of {sup 296}119 and {sup 295}119 isotopes are evaluated by means of a modified fusion-by-diffusion model. In the model, the dynamic evolution from dinucleus to mononucleus is taken into account with the two-dimensional coupled Langenvin equations. The calculated maximum ER cross sections in 3n and 4n evaporation channels of the {sup 50}Ti + {sup 249}Bk reaction are 0.17 and 0.57 pb, respectively. The cross section of 0.57 pb is close to the present experimental limit for the registration of the evaporation residual nuclei. Therefore, superheavy element 119 may be the most hopeful new element with Z>118 to be synthesized under somehow improved experimental conditions in the near future.
A review of methods of efficient accounting for correlation and relativistic effects is presented. A considerable part of efforts for these approaches must be devoted to coping with integrations over spin-angular variables, occurring in the matrix elements of the operators under consideration. Efficient methods to find the abovementioned quantities are described, based on the use of symmetry properties of operators and matrix elements in three spaces (orbital, spin and quasispin), on second quantization in coupled tensorial form, and on graphical technique. This allows to study and to generate fairly accurate their spectroscopic data practically for any atom and ion of periodical table.
{alpha} decay of {sup 271-294}115 superheavy nuclei is studied using the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The predicted {alpha} half-lives of {sup 287}115 and {sup 288}115 nuclei and their decay products are in good agreement with experimental values. Comparison of {alpha} and spontaneous fission half-lives predicts four-{alpha} chains and three-{alpha} chains, respectively, from {sup 287}115 and {sup 288}115 nuclei and are in agreement with experimental observation. Our study predicts two-{alpha} chains from {sup 273,274,289}115, three-{alpha} chains from {sup 275}115, and four-{alpha} chains consistently from {sup 284,285,286}115 nuclei. These observations will be useful for further experimental investigation in this region.
The aim of the OLIMPIYA experiment is to search for and identify traces of heavy and superheavy nuclei of galactic cosmic rays (GCR) in olivine crystals from stony–iron meteorites serving as nuclear track detectors. The method is based on layer-by-layer grinding and etching of particle tracks in these crystals. Unlike the techniques of other authors, this annealing-free method uses two parameters: the etching rate along the track ( V {sub etch}) and the total track length ( L ), to identify charge Z of a projectile. A series of irradiations with different swift heavy ions at the accelerator facilities of GSI (Darmstadt) and IMP (Lanzhou) were performed in order to determine and calibrate the dependence of projectile charge on V {sub etch} and L . To date, one of the most essential results of the experiment is the obtained charge spectrum of GCR nuclei within the range of Z > 40, based on about 11.6 thousand processed tracks. As the result of data processing, 384 nuclei with charges Z ≥ 75 have been identified, including 10 nuclei identified as actinides (90 < Z < 103). Three tracks were identified to be produced by nuclei with charges 113 < Z < 129. Such nuclei may be part of the Island of Stability of transfermium elements.
The semi-empirical macroscopic-microscopic mass formula is further improved by considering some residual corrections. The rms deviation from 2149 known nuclear masses is significantly reduced to 336 keV, even lower than that achieved with the best of the Duflo-Zuker models. The {alpha}-decay energies of super-heavy nuclei, the Garvey-Kelson relations, and the isobaric multiplet mass equation (IMME) can be reproduced remarkably well with the model, and the predictive power of the mass model is good. With a systematic study of 17 global nuclear mass models, we find that the quadratic form of the IMME is closely related to the accuracy of nuclear mass calculations when the Garvey-Kelson relations are reproduced reasonably well. Fulfilling both the IMME and the Garvey-Kelson relations seem to be two necessary conditions for improving the quality of the model prediction. Furthermore, the {alpha}-decay energies of super-heavy nuclei should be used as an additional constraint on global nuclear mass models.
The current state of the problem of heavy-element production in the astrophysical r-process is surveyed. The nucleosynthesis process in the neutron-star-merger scenario, within which the problem of free-neutron source is solved, is considered most comprehensively. A model that describes well the observed abundances of heavy elements is examined. Theoretical approaches used in this model to calculate a number of features of short-lived neutron-rich nuclei are described. The contributions of various fission processes to the production of heavy elements are assessed. The possibility of superheavy-element production in the r-process is demonstrated.
The alpha-decay half-lives of recently synthesized superheavy nuclei (SHN) are investigated by employing a unified fission model (UFM) where a new method to calculate the assault frequency of alpha emission is used. The excellent agreement with the experimental data indicates the UFM is a useful tool to investigate these alpha decays. It is found that the alpha-decay half-lives become more and more insensitive to the Q{sub a}lpha values as the atomic number increases on the whole, which is favorable for us to predict the half-lives of SHN. In addition, a formula is proposed to compute the Q{sub a}lpha values for the nuclei with Z>=92 and N>=140 with a good accuracy, according to which the long-lived SHN should be neutron rich. Several weeks ago, two isotopes of a new element with atomic number Z=117 were synthesized and their alpha-decay chains have been observed. The Q{sub a}lpha formula is found to work well for these nuclei, confirming its predictive power. The experimental half-lives are well reproduced by employing the UFM with the experimental Q{sub a}lpha values. This fact that the experimental half-lives are compatible with experimental Q{sub a}lpha values supports the synthesis of a new element 117 and the experimental measurements to a certain extent.
An approach we have proposed recently for calculation of Q{sub {alpha}} energy and decay half-life T{sub 1/2}{sup {alpha}} on the {alpha} decay of radioactive heavy ions is applied to the evaluation of these two important parameters for the nuclei in the superheavy region Z = 112-118 for which experimental data are not available. It is shown that the {alpha} + nucleus potential represented by an exactly solvable potential used in the calculation could be expressed in terms of proton (Z) and neutron (N) numbers of the {alpha} emitter so that varieties of {alpha}-emitting nuclei differing in their Z and N values could be addressed for their decay properties without the help of any adjustable parameter and the results of Q{sub {alpha}} and T{sub 1/2}{sup {alpha}} for a nucleus are estimated without any prior knowledge of any one of these quantities. This procedure to obtain the values of Q{sub {alpha}} and T{sub 1/2}{sup {alpha}} works well to reproduce the known experimental results for superheavy nuclei and hence, the procedure is expected to provide proper information about these parameters in experiments on {alpha} decay of new nuclei in the superheavy region.
Within the framework of a dinuclear system model, a new master equation is constructed and solved, which includes the relative distance of nuclei as a new dynamical variable in addition to the mass asymmetry variable so that the nucleon transfer, which leads to fusion and the evolution of the relative distance, which leads to quasifission (QF) are treated simultaneously in a consistent way. The QF mass yields and evaporation residual cross sections to produce superheavy nuclei are systematically investigated under this framework. The results fit the experimental data well. It is shown that the Kramers formula gives results of QF, which agree with those by our diffusion treatment, only if the QF barrier is high enough. Otherwise some large discrepancies occur.
The new, neutron-deficient, superheavy element isotope {sup 285}114 was produced in {sup 48}Ca irradiations of {sup 242}Pu targets at a center-of-target beam energy of 256 MeV (E* = 50 MeV). The {alpha} decay of {sup 285}114 was followed by the sequential {alpha} decay of four daughter nuclides, {sup 281}Cn, {sup 277}Ds, {sup 273}Hs, and {sup 269}Sg. {sup 265}Rf was observed to decay by spontaneous fission. The measured {alpha}-decay Q values were compared with those from a macroscopic-microscopic nuclear mass model to give insight into superheavy element shell effects. The {sup 242}Pu({sup 48}Ca,5n){sup 285}114 cross section was 0.6{sub -0.5}{sup +0.9} pb.
No abstract prepared.
Systematic calculations on the {alpha}-decay half-lives of heavy and superheavy nuclei are performed within a deformed version of the cluster model, using the modified two-potential approach. The deformed Woods-Saxon potential is employed to calculate the {alpha}-decay width through a deformed barrier. For comparison the calculated {alpha}-decay half-lives in the empirical relations are also presented. The present study is initially restricted to even-even nuclei in the heavy mass region with N>126. Then the study is extended to the recently observed heaviest nuclei, including synthesized superheavy elements and isotopes. The {alpha}-decay half-lives obtained are found to be in good agreement with the experimental data.
Theoretical models of superheavy elements (SHEs) predict a region of increased stability around the proton and neutron shell closures of Z = 114 and N = 184. Therefore a sensitive search for nuclides in the mass range from A = 288 to A = 300 was performed in natural platinum, lead, and bismuth, covering long-lived isotopes of Eka-Pt (Ds, Z = 110), Eka-Pb (Z = 114), and Eka-Bi (Z = 115). Measurements with accelerator mass spectrometry (AMS) at the Vienna Environmental Research Accelerator (VERA) established upper limits for these SHE isotopes in Pt, Pb, and Bi with abundances of <2x10{sup -15}, <5x10{sup -14}, and <5x10{sup -13}, respectively. These results complement earlier searches for SHEs with AMS at VERA in natural thorium and gold, which now amounts to a total number of 37 SHE nuclides having been explored with AMS. In none of our measurements was evidence found for the existence of SHEs in nature at the reported sensitivity level. Even though a few events were observed in the window for {sup 293}Eka-Bi, a particularly strong pileup background did not allow a definite SHE isotope identification. The present result sets limits on nuclides around the center of the island of stability, essentially ruling out the existence of SHE nuclides with half-lives longer than {approx}150 million years.