Long-lived Superheavy Elements Research Articles

Laser Spectroscopy of the Heaviest Elements: One Atom at a Time

The periodic table of elements experienced one of its biggest upheavals with the manifestation of the actinide series and the discovery of the first man-made superheavy elements (SHEs) in the early 1960s. Since then a genuine rally toward the production of ever heavier elements has been initiated, fueled by the promise from nuclear models of enhanced nuclear stability of SHEs around atomic numbers Z = 114 ~ 126 and neutron number N = 184. The potential existence of long-lived SHEs inspired scientists to search for them in nature while awaiting discovery with contemporary element production techniques. To date, the periodic table ends at element 118, oganesson (Og) [1], which has been named only recently together with the elements 113 (nihonium, Nh), 115 (moscovium, Mc), and 117 (tennessine, Ts).

Mass spectrometric searches for superheavy elements in terrestrial matter

Recent searches for traces of long-lived superheavy elements (SHEs) in terrestrial materials by mass spectrometric means are reviewed. Positive evidence for long-lived neutron-deficient Th isotopes in Th and Rg isotopes in Au, and a possible A=292, Z∼122 nuclide in Th was reported from experiments with Inductively Coupled Plasma Sector Field Mass Spectrometry (ICP-SF-MS). These findings were not confirmed with Accelerator Mass Spectrometry (AMS), with abundance limits lower by several orders of magnitude. In addition, the extensive AMS searches for 42 SHE nuclides (A=288–310) around the much discussed “island of stability” (Z=114, N=184) in natural Pt, Au, Pb, Bi materials are reviewed. Due to the flatness of the mass distribution and the relatively large bandwidth of the mass acceptance in AMS searches, an effectively much larger number of SHE nuclides was scanned in the respective materials. No positive evidence for the existence of long-lived SHEs (t1/2>108 yr) with abundance limits of 10−12 to 10−16 was found.

Search for superheavy elements with292⩽A⩽310in nature with accelerator mass spectrometry

There is a possibility that small traces of long-lived superheavy elements ($Z\ensuremath{\geqslant}104$) still exist in nature. An ultrasensitive search for such superheavy elements has been conducted at the Maier-Leibnitz Laboratory in Garching (Germany) by means of accelerator mass spectrometry. A sample of raw platinum has been scanned for 13 different masses in the range $292\ensuremath{\leqslant}A\ensuremath{\leqslant}310$. The masses $A=292$ and 298 were scanned in pure osmium and pure lead fluoride, respectively. For each mass, several hours of background-free data were recorded. Since no events could be attributed to superheavy elements, upper limits on their abundances in the sample materials on the order of ${10}^{\ensuremath{-}14}$--${10}^{\ensuremath{-}16}$ were established.

Synthesis and Properties of Superheavy Elements

This paper, presented at a RAS Presidium meeting, deals with the synthesis of relatively long-lived superheavy elements with atomic numbers 114 to 118. It was carried out at the Joint Institute for Nuclear Research by Academician Yu.Ts. Oganesyan’s research team. The focus was on the discovery of a new region of stability of superheavy elements.

Analysis and application of heavy isotopes in the environment

Abstract A growing number of AMS laboratories are pursuing applications of actinides. We discuss the basic requirements of the AMS technique of heavy (i.e., above ∼150 amu) isotopes, present the setup at the Vienna Environmental Research Accelerator (VERA) which is especially well suited for the isotope 236 U, and give a comparison with other AMS facilities. Special emphasis will be put on elaborating the effective detection limits for environmental samples with respect to other mass spectrometric methods. At VERA, we have carried out measurements for radiation protection and environmental monitoring ( 236 U, 239,240,241,242,244 Pu), astrophysics ( 182 Hf, 236 U, 244 Pu, 247 Cm), nuclear physics, and a search for long-lived super-heavy elements ( Z > 100). We are pursuing the environmental distribution of 236 U, as a basis for geological applications of natural 236 U.

Search for a superheavy nuclide with A=292 and neutron-deficient thorium isotopes in natural thorianite

In the search for long-lived superheavy elements (SHEs) in nature the claim for the detection of a SHE species with A = 292 in a commercially available thorium solution at an abundance of (1–10) × 10−12 relative to 232Th using ICP-SFMS has been raised very recently by Marinov et al. The same group also claimed the finding of four long-lived isomeric states in neutron-deficient thorium isotopes at an abundance of (1–10) × 10−11 relative to 232Th using the same experimental method. The aim of our study was to examine, whether the ratios mentioned above could also be found in a natural thorium mineral, using AMS as a much more sensitive technique assuring the complete suppression of molecular background. Chemically untreated thorianite (ThO2) was used for both measurements. In addition, commercial thorium(IV) oxide (thoria) powder was also analyzed in the SHE measurements. No events were observed in the A = 292 SHE search, resulting in an upper limit of 4 × 10−15 for the abundance of such a species relative to 232Th. For two neutron-deficient thorium isotopes, 211Th and 218Th, we find upper limits of 5 × 10−15. For 213Th and 217Th we observed a few events – albeit uncertain – which would put their abundance also into the 10−15 range.

Shape coexistence and triaxiality in the superheavy nuclei

Superheavy nuclei represent the limit of nuclear mass and charge; they inhabit the remote corner of the nuclear landscape, whose extent is unknown. The discovery of new elements with atomic numbers Z > or = 110 has brought much excitement to the atomic and nuclear physics communities. The existence of such heavy nuclei hangs on a subtle balance between the attractive nuclear force and the disruptive Coulomb repulsion between protons that favours fission. Here we model the interplay between these forces using self-consistent energy density functional theory; our approach accounts for spontaneous breaking of spherical symmetry through the nuclear Jahn-Teller effect. We predict that the long-lived superheavy elements can exist in a variety of shapes, including spherical, axial and triaxial configurations. In some cases, we anticipate the existence of metastable states and shape isomers that can affect decay properties and hence nuclear half-lives.

Synthesis of superheavy nuclei in the reactions of 244Pu and 248Cm with 48Ca

This paper presents results of the experiments aimed at producing long-lived superheavy elements located near the spherical-shell closures with Z ⩾ 114 and N ⩾ 172 in the 244Pu + 48Ca and 248Cm + 48Ca reactions. The large measured α-particle energies of the newly observed nuclei, together with the long decay times and spontaneous fission terminating the chains, offer evidence of the decay of nuclei with high atomic numbers. The decay properties of the synthesized nuclei are consistent with the consecutive α-decays originating from the parent nuclides 288, 289114 and 292116, produced in the 3n and 4n evaporation channels with cross-sections of about a picobarn. The present observations can be considered as experimental evidence of the existence of the “island of stability” of superheavy elements.

A new hypothesis for the existence of superheavy elements in the earth"s crust

In a new hypothesis the existence of superheavy elements (SHE) in the earth"s crust that decays by spontaneous fission into two unequal fragments around 50 and 230 is postulated. Several phenomena such as excesses of stable and unstable isotopes and radioactive daughter isotopes in natural decay series are interpreted as fission fragments of spontaneously splitting long-lived SHE. These phenomena are only indirect indications, not a proof of the existence of SHE.

The Synthesis and Properties of Superheavy Nuclei Produced in the 48 Ca+ 244 Pu, 248 Cm Reactions

We present the results of the experiments aimed at producing hypothetical long-lived superheavy elements located near the spherical shell closures with Z>-114 and N>-172. For the synthesis of superheavy nuclei a combination of neutron-rich reaction partners, such as 244Pu and 248Cm targets and a 48Ca projectile have been used. The sensitivity of the present experiment exceeded by more than two orders of magnitude previous attempts to synthesize superheavy nuclides in reactions of 48Ca projectiles with actinide targets. We observed new decay sequences of genetically linked α-decays terminated by spontaneous fission. The decay properties of the synthesized nuclei are consistent with the consecutive α-decays originating from the parent nuclides 288,289114, produced in the 3n and 4n-evaporation channels, and 292116 — in the 4n-evaporation channel with cross sections of about a picobarn. The present observations can be considered an experimental evidence of the existence of the “island of stability” of superheavy elements and are discussed in terms of modern theoretical approaches.

STRONGLY ENHANCED LOW ENERGY α-PARTICLE DECAY IN HEAVY ACTINIDE NUCLEI AND LONG-LIVED SUPERDEFORMED AND HYPERDEFORMED ISOMERIC STATES

Unidentified low energy and very enhanced α-particle groups have been observed in various actinide fractions produced via secondary reactions in a CERN W target which had been irradiated with 24-GeV protons. In particular, 5.14, 5.27 and 5.53 MeV α-particle groups with corresponding half-lives of 3.8±1.0 y, 625±84 d and 26±7d, have been seen in Bk, Es and Lr-No sources, respectively. The measured energies are a few MeV lower than the known ground state to ground state α-decays in the corresponding neutron-deficient actinide nuclei. The half-lives are 104to 107shorter than expected from energy versus lifetime relationship for such low-energy α-particles in this region of nuclei. The deduced evaporation residue cross sections are in the mb region, about 104times higher than expected. Not only is it impossible to identify these α-decays with any known activity in the whole nuclear chart, but they also could not be due to hypothetically unknown isomeric states in various conceivable neutron deficient nuclei, nor due to unknown isomeric states in the rare-earth region. Based on the fact that in other experiments we have found isomeric states in the second and third minima of the potential for other heavy ion reaction products, one can now understand in a quantitative way, both the unusual low energies, the unusual enhanced lifetimes and the unusual large production cross sections, in terms of production of similar isomeric states in appropriate actinide isotopes. Some consequences regarding the production of the long-lived superheavy elements are also discussed.

Synthesis of superheavy nuclei in 48Ca+244Pu interactions

This article reports the results of experiments aimed at producing hypothetical long-lived superheavy elements located near the spherical-shell closures with Z≥114 and N≥72. For the synthesis of superheavy nuclei, we used a combination of neutron-rich reaction partners, with a 244Pu target and a 48Ca projectile. The sensitivity of the present experiment exceeded by more than two orders of magnitude previous attempts at synthesizing superheavy nuclides in reactions of 48Ca projectiles with actinide targets. We observed new decay sequences of genetically linked alpha decays terminated by spontaneous fission. The high measured alpha-particle energies, together with the long decay times and spontaneous fission terminating the chains, offer evidence for the decay of nuclei with high atomic numbers. The decay properties of the synthesized nuclei are consistent with the consecutive alpha decays originating from the parent nuclides 288,289114, produced in the 3n-and 4n-evaporation channels with cross sections of about a picobarn. The present observations can be considered experimental evidence for the existence of the “island of stability” of superheavy elements and are discussed in terms of modern theoretical approaches.

Isomeric states in the second well of the potential and long-lived superheavy elements

The data on long-lived isomeric states obtained via secondary reactions in CERN W targets irradiated with 24 GeV protons and also by the16O+197Au and28Si+181Ta reactions are summarized. Their consequences concerning the existence and the discovery of the long-lived superheavy element withZ=112 are discussed.

Search for long-lived superheavy elements in the reaction of136Xe with238U

A search with radiochemical methods for long-lived superheavy elements in 238U targets bombarded with intense beams of136Xe ions produced negative results. A formation cross section of ≤1×10−35 cm2 is deduced at 95% confidence level for nuclides with half-lives between 1 and 200 d.