Synthesis of transactinide nuclei in cold fusion reactions using radioative beams

Chances of synthesis of transactinide nuclei in cold fusion reactions (one-neutron-out) reactions using radioactive beams are evaluated. Because intensities of radioactive beams are in most of the cases significantly lower than the ones of the stable beams, reactions with the highest radioactive beam intensities for the particular elements are considered. The results are compared with the recent ones obtained by Loveland who investigated the same nuclei.Comment: 5 page

Cross Section Limits for the 208^{208}Pb(86^{86}Kr,n)293^{293}118 Reaction

In April-May, 2001, the previously reported experiment to synthesize element 118 using the $^{208}$Pb($^{86}$Kr,n)$^{293}$118 reaction was repeated. No events corresponding to the synthesis of element 118 were observed with a total beam dose of 2.6 x 10$^{18}$ ions. The simple upper limit cross sections (1 event) were 0.9 and 0.6 pb for evaporation residue magnetic rigidities of 2.00 $T m$ and 2.12 $T m$, respectively. A more detailed cross section calculation, accounting for an assumed narrow excitation function, the energy loss of the beam in traversing the target and the uncertainty in the magnetic rigidity of the Z=118 recoils is also presented. Re-analysis of the primary data files from the 1999 experiment showed the reported element 118 events are not in the original data. The current results put constraints on the production cross section for synthesis of very heavy nuclei in cold fusion reactions.Comment: 7 pages, 2 figures. Submitted to EPJ

Shell stabilization of super- and hyperheavy nuclei without magic gaps

Quantum stabilization of superheavy elements is quantified in terms of the shell-correction energy. We compute the shell correction using self-consistent nuclear models: the non-relativistic Skyrme-Hartree-Fock approach and the relativistic mean-field model, for a number of parametrizations. All the forces applied predict a broad valley of shell stabilization around Z=120 and N=172-184. We also predict two broad regions of shell stabilization in hyperheavy elements with N approx 258 and N approx 308. Due to the large single-particle level density, shell corrections in the superheavy elements differ markedly from those in lighter nuclei. With increasing proton and neutron numbers, the regions of nuclei stabilized by shell effects become poorly localized in particle number, and the familiar pattern of shells separated by magic gaps is basically gone.Comment: 6 pages REVTEX, 4 eps figures, submitted to Phys. Lett.

Semiempirical Shell Model Masses with Magic Number Z = 126 for Superheavy Elements

A semiempirical shell model mass equation applicable to superheavy elements up to Z = 126 is presented and shown to have a high predictive power. The equation is applied to the recently discovered superheavy nuclei Z = 118, A = 293 and Z = 114, A = 289 and their decay products.Comment: 7 pages, including 2 figures and 2 table

Particle-drip lines from the Hartree-Fock-Bogoliubov theory with Skyrme interaction

We calculate positions of one- and two-particle, proton and neutron drip lines within the Hartree-Fock-Bogoliubov theory using Skyrme interaction. We also determine an approximate $r$-process path defined as a line where the neutron binding energy is equal to 2~MeV. A weakening of the nuclear shell structure at drip lines is found and interpreted as resulting from a coupling with continuum states.Comment: 10 pages REVTEX 3.0, 3 uuencoded postscript figures included, IFT/14/9

Shell Structure of the Superheavy Elements

Ground state properties of the superheavy elements (SHE) with Z from 108 to 128 and N from 150 to 192 are investigated using both the Skyrme-Hartree-Fock method with a density-independent contact pairing interaction and the macroscopic-microscopic approach with an average Woods-Saxon potential and a monopole pairing interaction. Detailed analysis of binding energies, separation energies, shell effects, single proton and neutron states, equilibrium deformations, alpha-decay energies, and other observables is given.Comment: 27 RevTeX pages, 22 figures available upon request to [email protected]

Continuum Linear Response in Coordinate Space Hartree-Fock-Bogoliubov Formalism for Collective Excitations in Drip-line Nuclei

We formulate a continuum linear response theory on the basis of the Hartree-Fock-Bogoliubov formalism in the coordinate space representation in order to describe low-lying and high-lying collective excitations which couple to one-particle and two-particle continuum states. Numerical analysis is done for the neutron drip-line nucleus $^{24}$O. A low-lying collective mode that emerges above the continuum threshold with large neutron strength is analyzed. The collective state is sensitive to the density-dependence of the pairing. The present theory satisfies accurately the energy weighted sum rule. This is guaranteed by treating the pairing selfconsistently both in the static HFB and in the dynamical linear response equation.Comment: 19 pages, 6 figure

Deformation of Nuclei Close to the Two-Neutron Drip Line in Mg Region

We perform the Hartree-Fock-Bogoliubov (HFB) calculations for ground states of even Mg isotopes using the Skyrme force and a density-dependent zero-range pairing force. The HFB equation is solved in a three-dimensional cartesian mesh, and a convergence of deformation is carefully examined with respect to a cut-off radius for a check of the calculations. We discuss systematics of the two-neutron separation energy, deformation and root-mean-square radius. We have found that 36,38,40Mg have appreciable static deformation, where 40Mg is a two-neutron drip-line nucleus in our calculation, and the deformations of the neutron and proton are different in these three nuclei. The deformation property is analyzed on the basis of the single-particle diagram. It is shown that N=28 is not a closed shell in Mg as well as Si.Comment: 13 pages, 8 Postscript figures, submitted to Nucl.Phy

Effect of differences in proton and neutron density distributions on fission barriers

The neutron and proton density distributions obtained in constrained Hartree-Fock-Bogolyubov calculations with the Gogny force along the fission paths of 232Th, 236U, 238U and 240Pu are analyzed. Significant differences in the multipole deformations of neutron and proton densities are found. The effect on potential energy surfaces and on barrier heights of an additional constraint imposing similar spatial distributions to neutrons and protons, as assumed in macroscopic-microscopic models, is studied.Comment: 5 pages in Latex, 4 figures in ep

alpha-decay chains of Z=114, A=289 and Z=118, A=293 in the relativistic mean-field model

A comparison of calculated and experimental Q_alpha values of superheavy even-even nuclei and a few selected odd-N nuclei is presented in the framework of the relativistic mean-field model with the parameterization NL-Z2. Blocking effects are found to be important for a proper description of Q_alpha of odd mass nuclei. The model gives a good overall description of the available experimental data. The mass and charge assignment of the recently measured decay chains from Dubna and Berkeley is in agreement with the predictions of the model. The analysis of the new data does not allow a final conclusion about the location of the expected island of spherical doubly-magic superheavy nuclei.Comment: 4 pages REVTeX, 4 eps figures, accepted for publication in Phys. Rev.