On the possible existence of superheavy elements in monazite

Proton-induced x-ray studies of monazite grains from different occurrences show no evidence for primordial superheavy elements. It is demonstrated that the recently reported evidence for superheavy elements in monazite inclusions of biotite mica showing giant halo formation is not significant: the observed differences in the x-ray spectra of normal and giant halo inclusions are due to different backgrounds in the respective spectra. Moreover, it is shown that the 27.2 keV line tentatively interpreted as theL _α1x-ray of elementZ=126 can be entirely attributed to the reaction¹⁴⁰Ce(p,n γ)¹⁴⁰Pr.     

New attempts in search for superheavy elements in nature

A new procedure in search for superheavy elements (SHE) in nature is suggested. SSNTD and crown-ethers will be employed in this work.     

Magic numbers in superheavy elements

The energy density method is used to study the magic character of neutron and proton numbers corresponding to N > 126 and Z > 82. It is found that N = 184 and N = 228 are the next neutron magic numbers. For the protons, however, no sign of a shell closure appears for 82 < Z ? 130. Some simple criteria for the β^? - and α-stability of N = 184 and N = 228 isotones are also discussed.     

New analog electronics for the new challenges in the synthesis of superheavy elements

A new series of experiments aimed at the synthesis and study of decay properties of the most neutron-deficient isotopes of element Fl (Z = 114) and of the heaviest isotopes of 118 element is planned at the DGFRS (FLNR JINR). An appropriate registering system is to be implemented to transfer spectrometric data from double-sided silicon strip detector (DSSD). New analog modules were designed that allow to simplify existing multi-channel measurement system and to improve the real-time method of “active correlations” in search for the rare events of SHE formation and decay. The main features of the new modules the 16-channel charge-sensitive preamplifier, the 16-channel analog multiplexer and the 1.25 MSPS 12-bit Parallel ADC are presented.     

On the production of superheavy elements

Since the discovery of Deformed Superheavy Nuclei (1983–85) a bridge connects the island of SHE to known isotopes of lighter elements. What we know experimentally and theoretically on the nuclear structure of SHE is reported in a first section. The making of the elements, with an analysis of production cross sections, and the macroscopic limitation to Z=112+ε is presented in a second section. The break-down of fusion cross sections in the ‘Coulomb Falls’ within a range of about 10 elements is introduced as the universal limiting phenomenon. How the nuclear structure of the collision partners modifies the on-set of this limitation is presented in Section 3. Reactions induced by deformed nuclei are pushed by side collisions to higher excitation energies (4n- and 5n-channels), whereas reactions driven by the cluster-like, closed-shell nuclei, ²⁰⁸₁₂₆Pb and ¹³⁸₈₂Ba, are kept at low excitation energies (1n- and 2n-channels). The on-set of production limitation for deformed collision partners is moved to smaller effective fissilities x=0.68⩽0.72, whereas for spherical clusters the on-set is delayed x=0.76⩾0.72 and x=0.79⩾0.72 for ¹³⁸Ba and ²⁰⁸Pb, respectively. An outlook, what remains to be studied in the future, ends the article. To cite this article: P. Armbruster, C. R. Physique 4 (2003).     

Transition rates of electrons in superheavy elements

Transition rates for electrons in the superheavy elementsZ=114, 126, 134, 145, 164 and 173 are calculated.K, L andM-shells are considered as final states. The 2s-1s transition of multipolarityM 1 is dominant for Z = 173 with a transition time of 10^?18 s. The radical expectation values 〈r〉 and 〈r²〉^1/2 are given.     

The relative stability of superheavy elements

The relative stability of superheavy elements against beta-decay and spontaneous fission has been investigated. A simple criterion of beta-stability using the Fermi gas model has been developed, tested in the range of stable nuclei and extended to the superheavy region. Spontaneous fission half-lives have been calculated using the statistical model in the expected region of relative beta-stability for superheavy nuclei. Our results have been compared with previous calculations.     

Theory of fusion for superheavy elements

A new model is proposed for fusion mechanisms of massive nuclear systems, where so-called fusion hindrance exists. The model describes the whole process in two steps: two-body collision processes in an approaching phase and shape evolutions of an amalgamated system into the compound nucleus formation. It is applied to ⁴⁸Ca-induced reactions and is found to reproduce the experimental fusion cross sections extremely well, without any free parameter. A schematic case is solved in an analytic way, the results of which shed light on fusion mechanisms. Combined with statistical decay theory, residue cross sections for superheavy elements can be readily calculated. Examples are given.     

Fusion theory for synthesis of the superheavy elements

Recent developments on reaction mechanisms in fusion of massive systems are briefly reviewed, especially on a two-step model. The fusion hindrance observed experimentally is simply explained in connection with the fluctuation-dissipation dynamics of shape evolutions and of two-body collisions. Examples are given for fusion excitation functions and compared with the available data on ⁴⁸Ca+actinide target systems.     

QED and relativistic corrections in superheavy elements

In this paper we review the different relativistic and QED contributions to energies, ionic radii, transition probabilities and Landé g-factors in super-heavy elements, with the help of the MultiConfiguration Dirac-Fock method (MCDF). The effects of taking into account the Breit interaction to all orders by including it in the self-consistent field process are demonstrated. State of the art radiative corrections are included in the calculation and discussed. We also study the non-relativistic limit of MCDF calculation and find that the non-relativistic offset can be unexpectedly large.     

The possible existence of Hs in nature from a geochemical point of view

A hypothesis of the existence of a long-lived isotope ²⁷¹Hs in natural molybdenites and osmirides is considered from a geochemical point of view. It is shown that the presence of Hs in these minerals can be explained only by making an additional ad hoc assumption on the existence of an isobaric pair of ²⁷¹Bh-²⁷¹Hs. This assumption could be tested by mass-spectrometric measurements of U, Pb, Kr, Xe, and Zr isotopic shifts.     

Effect of the entrance channel on the synthesis of superheavy elements

Cross-sections for the synthesis of superheavy elements were analyzed using the concept of a dinuclear system. Experimental values for the production of elements Z = 104, 108, 110, 111 and 112 by cold fusion reactions with targets of ²⁰⁸Pb and ²⁰⁹Bi were reproduced. The model reveals the importance of entrance channel dynamics and competition between quasi-fission and complete fusion processes. Energy windows were observed which allow capture of the reacting nuclei and formation of the compound nucleus. The quantities were studied which are significant for the interaction dynamics of massive nuclei in the entrance channel.     

Status and prospects of synthesizing superheavy elements

The nuclear shell model predicts that the next doubly magic shell-closure beyond ²⁰⁸Pb is at a proton number between Z = 114 and 126 and at a neutron number N = 184. The outstanding aim of experimental investigations is the exploration of this region of spherical “Superheavy Elements”. This article describes the experiments that were performed at the GSI SHIP. They resulted in an unambiguous identification of elements 107 to 112. They were negative so far in searching for elements 113, 116 and 118 at SHIP; however, positive results were reported from experiments in Dubna on elements 114 and 116 and from experiments in Berkeley on element 118. The measured decay data are compared with theoretical predictions. Some aspects concerning the reaction mechanism and the use of radioactive beams are also presented. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: S.Hofmann@gsi.de     

Advances in the search for superheavy elements at GSI

The nuclear shell model predicts that the next doubly magic shell-closure beyond ²⁰⁸Pb is at a proton number between Z=114 and 126 and at a neutron number N=184. The outstanding aim of experimental investigations is the exploration of this region of spherical ‘SuperHeavy Elements’ (SHE’s). This article describes the experiments that were performed at GSI, Darmstadt. They resulted in an unambiguous identification of elements 107 to 112. They were negative so far in searching for elements 113, 116 and 118. Plans are presented for an upgrade of the experimental set-up aiming at an improved sensitivity for further exploration of SHE’s.     

Reaction dynamics of synthesis of superheavy elements

Based on the theory of the compound nucleus reaction, a brief review is given on the special aspects of the reaction dynamics in the synthesis of the superheavy elements (SHE), where the fusion probability is the most unknown factor. A new viewpoint of the fusion reaction is proposed that it consists of two processes; the first process up to the contact of two nuclei of the incident channel and the second one of a dynamical evolution to the spherical compound nucleus from the contact configuration. The fusion probability is, thus, given as a product of a contact probability and a formation probability. Analytic studies of the latter probability are discussed in the one-dimensional model, where a simple expression is given to the so-called extra-push energy in terms of the reduced friction, the curvature parameter of the conditional saddle point and the nuclear temperature. Preliminary results of numerical analyses of the contact probability are given, using the surface friction model (SFM). Remarks are given on the present status of our knowledge and for future developments. Received: 1 May 2001 / Accepted: 4 December 2001     

Search for superheavy elements in galactic cosmic rays

The charge distribution of approximately 6000 nuclei with charge numbers above 55 in galactic cosmic rays has been obtained in the OLIMPIYA project. Three superheavy nuclei with the charge numbers in the range 105 < Z < 130 have been detected. The regression analysis has provided a more accurate estimate of the charge number of one of these nuclei (119 _?6 ⁺¹⁰ with a probability of 95%). Such nuclei should form stability islands. Their detection in nature confirms theoretical predictions and justifies efforts for their synthesis under terrestrial conditions. The model calculations performed in this work possibly can explain the results of some experiments on the investigation of the charge composition of cosmic rays in which particles with charge numbers in the range 94 < Z < 100 were detected (they cannot enter into the composition of primary cosmic radiation because their lifetime is very short). The calculations indicate that events with Z > 92 are due to the fragmentation of heavier nuclei from the stability island, rather than to methodical inaccuracies or fault of instruments. Several such events have been revealed. Thus, the track method makes it possible to obtain the results very important for understanding of the physical picture of the world. The results obtained within the OLIMPIYA project show that the study of tracks of galactic cosmic rays in olivine crystals from meteorites opens new capabilities for the investigation of fluxes and spectra in cosmic rays in the region of heavy and superheavy nuclei.     

Fusion hindrance and synthesis of superheavy elements

A mechanism for fusion hindrance is clarified, based on the observation that the sticking configuration of projectile and target is located outside of the conditional saddle point. Accordingly, the fusion process is described by two sequential steps of passing over the Coulomb barrier and shape evolution toward the spherical compound nucleus. The latter one is indispensable in massive systems. With the use of a two-step model, excitation functions of fusion reaction are calculated for various combinations of projectiles and targets which lead to superheavy elements. The hindered fusion excitation measured is reproduced precisely without any adjustable parameter. Combined with survival probabilities calculated by the statistical theory of decay, excitation functions for residues of superheavy elements are calculated to compare with the systematic data measured for the cold fusion path. The peak positions and the widths are correctly reproduced, though it is necessary to reduce the shell correction energies of the compound nuclei predicted by the structure calculations in order to reproduce their absolute values. Predictions are made for a few unknown heavier elements. Furthermore, a preliminary attempt toward the shell closure N = 184 is also presented using a neutron-rich secondary beam. The text was submitted by the authors in English.     

Shell structure and stability of nuclei with 270<A<500 and the possible existence of primordial superheavy nuclei

The self-consistent energy density method is applied to the study of the properties of superheavy nuclei with 270<A<500. The shell structure,α-decay energy andα-decay half-life are predicted for the heaviestβ-stable isotope of each even element. The characteristics of nuclear densities and single-particle potentials in the superheavy region are also examined, with a particular attention on the surface diffuseness. After an approximate calculation of their fission barrier heights, only a few heavy isotopes of elements 106 and 108 are predicted to have a small chance to be found in nature. Their possible formation by ther-process is discussed.     

Route to islands of stability of superheavy elements

Problems concerning the existence of hypothetical superheavy elements for which theoretical nuclear models predict high stability with respect to various modes of radioactive decay are discussed. The synthesis of superheavy nuclei and the possibilities for performing experiments aimed at detecting rare events of their production and decay in heavy-ion beams are considered. Experimental results suggesting a considerable increase in the lifetime of nuclei as they approach the closed proton and neutron shells determining the islands of stability of superheavy elements are presented.