Superheavy Elements In Nature Research Articles

The transuranic elements and the island of stability.

Since the 1930s the synthesis of nuclides too unstable to exist naturally on Earth has stretched the periodic table to 118 elements. While the lighter transuranic elements have found uses, the isotopes of those past lawrencium, the superheavy elements, are too unstable to exist outside the laboratory. In the 1970s, leading element discoverers Glenn Seaborg at the University of California, Berkeley, USA, and Georgy Flerov, at the Joint Institute for Nuclear Research in Dubna, USSR, took interest in a supposed 'island of stability', leading from the nuclear shell model of Maria Goeppert Mayer and Hans Jensen, and predicted elements with so-called magic numbers of protons and neutrons would be far more stable. This review shall look at the historical developments that led to the field of element discovery, the attempts to discover superheavy elements in nature based on the island of stability, and the subsequent successful synthesis of elements and the implications of their half-lives and properties. This article is part of the theme issue 'Mendeleev and the periodic table'.

β-delayed Fission in r-process Nucleosynthesis

Abstract We present β-delayed neutron emission and β-delayed fission (βdf) calculations for heavy, neutron-rich nuclei using the coupled Quasi-Particle Random Phase Approximation plus Hauser-Feshbach (QRPA+HF) approach. From the initial population of a compound nucleus after β-decay, we follow the statistical decay, taking into account competition between neutrons, γ-rays, and fission. We find a region of the chart of nuclides where the probability of βdf is ∼100%, which likely prevents the production of superheavy elements in nature. For a subset of nuclei near the neutron dripline, neutron multiplicity and the probability of fission are both large, leading to the intriguing possibility of multi-chance βdf, a decay mode for extremely neutron-rich heavy nuclei. In this decay mode, β-decay can be followed by multiple neutron emission, leading to subsequent daughter generations that each have a probability to fission. We explore the impact of βdf in rapid neutron-capture process (r-process) nucleosynthesis in the tidal ejecta of a neutron star–neutron star merger and show that it is a key fission channel that shapes the final abundances near the second r-process peak.

Erratum to: “Formation of Superheavy Elements in Nature”

The list of affiliations should read: Institute for Theoretical and Experimental Physics, National Research Center Kurchatov Institute, Bol’shaya Cheremuskinskaya ul. 25, Moscow, 117218 Russia Sternberg Astronomical Institute (GAISh), Moscow State University, Universitetskii pr. 13, Moscow, 119992 Russia National Research Center “Kurchatov Institute”, pl. Akademika Kurchatova 1, Moscow, 123182, Russia

Formation of Superheavy Elements in Nature

It is shown that superheavy elements may also be formed in the main r process responsible for the formation of the heaviest elements observed in nature. Under conditions of a high neutron density, the nucleosynthesis region lies close to the neutron drip line, so that the r process may circumvent the region where nuclei undergo spontaneous fissions and therefore have short lifetimes. However, a high induced-fission rate, which increases with the charge number, may prevent the nucleosynthesis wave from overcoming the region of isotopes heavier than curium, and the beta-decay chain leading to an increase in the charge number of product elements inevitably results in the spontaneous fission of the majority of product nuclei. Calculations of nucleosynthesis that were performed with available nuclear data within the scenario of a neutron-star merger reveal that only Z < 106 superheavy elements are formed. Their abundance at the end of the r process is commensurate with the abundance of uranium, but their lifetime does not exceed several years, so that they fast undergo decay.

Searches for superheavy elements in nature: Cosmic-ray nuclei; spontaneous fission

There is little chance that superheavy nuclei with lifetimes of no less than 100 million years are present on the stability island discovered at present. Also, pessimistic are the results of estimates made about their nucleosynthesis in r-process. Nevertheless, the search for these nuclei in nature is justified in view of the fundamental importance of this topic. The first statistically significant data set was obtained by the LDEF Ultra-Heavy Cosmic-Ray Experiment, consisting of 35 tracks of actinide nuclei in galactic cosmic rays. Because of their exceptionally long exposure time in Galaxy, olivine crystals extracted from meteorites generate interest as detectors providing unique data regarding the nuclear composition of ancient cosmic rays. The contemporary searches for superheavy elements in the earth matter rely on knowledge obtained from chemical studies of artificially synthesized superheavy nuclei. New results finding out the chemical behavior of superheavy elements should be employed to obtain samples enriched in their homologues. The detection of rare spontaneous fission events and the technique of accelerator mass spectrometry are employed in these experiments.

Accelerator mass spectrometry – from DNA to astrophysics

A brief review of accelerator mass spectrometry (AMS) is presented. The present work touches on a few technical aspects and recent developments of AMS, and describes two specific applications of AMS, the dating of human DNA with the 14 C bomb peak and the search for superheavy elements in nature. Since two extended general reviews on technical developments in AMS [1] and applications of AMS [2] will appear in 2013, frequent reference to these reviews is made.

Ultrasensitive search for long-lived superheavy nuclides in the mass rangeA=288toA=300in natural Pt, Pb, and Bi

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 2\ifmmode\times\else\texttimes\fi{}10${}^{\ensuremath{-}15}$, 5\ifmmode\times\else\texttimes\fi{}10${}^{\ensuremath{-}14}$, and 5\ifmmode\times\else\texttimes\fi{}10${}^{\ensuremath{-}13}$, 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 $^{293}\mathrm{Ek}$a-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 \ensuremath{\sim}150 million years.

SYNTHESIS OF HEAVIEST ELEMENTS (RESULTS AND PROSPECTS)

The formation and decay properties of the heaviest nuclei with Z = 112 - 116 and 118 were studied in the reactions 238 U , 242,244 Pu , 243 Am , 245,248 Cm and 249 Cf +48 Ca . The new nuclides mainly undergo sequential α-decay, which ends with spontaneous fission. The total time of decays ranges from 0.5 ms to about 1 day, depending on the proton and neutron numbers in the synthesized nuclei. The atomic number of the new elements 115 and 113 was confirmed also by an independent radiochemical experiment based on the identification of the neutron-rich isotope 268 Db (TSF ≈ 30 h ), the final product in the chain of α-decays of the odd–odd parent nucleus 288115. The comparison of the decay properties of 29 new nuclides with Z = 104 - 118 and N = 162 - 177 gives evidence for the decisive influence of the structure of superheavy nuclei on their stability with respect to different modes of radioactive decay. The investigations connected with the search for superheavy elements in Nature (cosmic rays) and prospects of superheavy element research are also presented.

Synthesis and decay properties of the heaviest nuclei

The formation and decay properties of the heaviest nuclei with Z=112–116 and 118 were studied in the reactions 238U, 242,244Pu, 243Am, 245,248Cm and 249Cf + 48Ca. The new nuclides mainly undergo sequential α-decay, which ends with spontaneous fission. The total time of decay ranges from 0.5 ms to ∼1 day, depending on the proton and neutron numbers in the synthesized nuclei. The atomic number of the new elements 115 and 113 was confirmed also by an independent radiochemical experiment based on the identification of the neutron-rich isotope 268Db (TSF∼30 h), the final product in the chain of α-decays of the odd–odd parent nucleus 288115. The comparison of the decay properties of 29 new nuclides with Z=104–118 and N=162–177 gives evidence of the decisive influence of the structure of superheavy elements on their stability with respect to different modes of radioactive decay. The investigations connected with the search for superheavy elements in Nature and prospects of superheavy element research are also presented.The experiments were carried out at the Flerov Laboratory of Nuclear Reactions (JINR, Dubna) in collaboration with the Analytical and Nuclear Chemistry Division of the Lawrence Livermore National Laboratory (USA).

Synthesis and decay properties of superheavy elements

Abstract A fundamental outcome of modern nuclear theory is the prediction of the "island of stability" in the region of hypothetical superheavy elements. A significant enhancement in nuclear stability at approaching the closed shells with Z = 114 (possibly 120 and 122) and N = 184 is expected for the nuclei with large neutron excess. For this reason, for the synthesis of nuclei with Z = 112-116 and 118, we chose the reactions 238U, 242,244Pu, 243Am, 245,248Cm, and 249Cf + 48Ca, which are characterized by fusion products with a maximal neutron excess. The formation and decay properties of the heaviest nuclei were registered with the use of a gas-filled recoil separator installed at a 48Ca-beam of the heavy-ion cyclotron. The new nuclides mainly undergo sequential α-decay, which ends with spontaneous fission (SF). The total time of decay ranges from 0.5 ms to ~1 d, depending on the proton and neutron numbers in the synthesized nuclei. The atomic number of the new elements 115 and 113 was confirmed also by an independent radiochemical experiment based on the identification of the neutron-rich isotope 268Db (T SF ~ 30 h), the final product in the chain of α-decays of the odd-odd parent nucleus 288115. The comparison of the decay properties of 29 new nuclides with Z = 104-118 and N = 162-177 gives evidence of the decisive influence of the structure of superheavy elements on their stability with respect to different modes of radioactive decay. The investigations connected with the search for superheavy elements in Nature are also presented. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions (JINR, Dubna) in collaboration with the Analytical and Nuclear Chemistry Division of the Lawrence Livermore National Laboratory (USA).

Correlation between the Chemical Properties of Elements and Their Natural Abundance in the Context of the Search for Superheavy Elements in Nature

A study was made of the correlation between the chemical properties of elements [light homologsof superheavy elements (SHEs)], their levels in products of various endogenic geological processes andin substances of certain space bodies (in particular, the Tunguska meteorite) in order to gain insight intopossible distribution of SHEs in Solar system bodies. Physicochemical aspects of endogenic processes were discussed. It was shown that, along with geothermal brines (oceanic water), the most promising natural materials to be tested for SHEs are some volcanic (fumarole, griffon) products, lunar rocks, and asteroids. Certain differences in the elemental compositions of crude oil and living matter were discussed which suggest the presence in the crude oil of volatile components, including SHEs, and agree with Mendeleev's hypothesis of inorganic synthesis of oil.

On search and identification of relatively short-lived superheavy nuclei (Z ≥ 110) by fossil track studies of meteoritic and lunar olivine crystals

The main goal of the present work is the search for and identification of relatively stable nuclei of superheavy elements (SHE) (Z>110) in galactic matter by fossil track study of nonconducting crystals from the surface of meteorites and rocks from the lunar regolith. Nuclei of SHE are thought to be the products of nucleosynthesis in explosive processes in our Galaxy (supernova r-process nucleosynthesis and, especially, neutron-star formation, etc.). When accelerated to relativistic energies in the Galaxy, they can produce extended trails of damage in nonconducting extraterrestrial crystals. The lifetime of such SHE in galactic cosmic rays will range from 103 to 107 yr to be registered in extraterrestrial crystals. To search for and to identify the superheavy nuclei in the galactic cosmic rays, it was proposed to use the ability of nonconducting extraterrestrial crystals such as olivines, pyroxenes, and feldspars to detect and to store for many millions of years the trails of damage produced by fast Z≥23 nuclei coming to rest in the crystalline lattice. The track lengths of fast Z≥23 nuclei are directly proportional to Z2 of these nuclei. The nuclei of SHE produce, when coming to rest in a crystal volume, tracks that are a factor of 1.6–1.8 longer than the tracks due to cosmic-ray Th and U nuclei. To identify the tracks due to superheavy nuclei, calibrations of the same crystals were performed with accelerated Au, Pb, and U nuclei. For visualization of these tracks inside the crystal volume, proper controlled annealing and chemical etching procedures were developed. Since 1980, fossil tracks due to Th and U nuclei have observed and unambiguously identified (1988) by subsequent calibrations of the olivine crystals with accelerated U, Au, and Pb ions. The number of tracks of Th and U nuclei measured in olivine crystals totaled more than 1600, as compared with the prior 30 events. The other approach to identifying SHE in nature is to search for tracks in phosphate crystals from spontaneous fission of Z ≥ 110 nuclei; these produce two-prong and three-prong fission fragment tracks and differ significantly from the tracks from spontaneous fission of 238U and 244Pu nuclei. Extraterrestrial phosphate crystals of lunar and meteoritic origin will be investigated. Such SHE nuclei can survive in crystals of extraterrestrial rocks and produce spontaneous fission tracks, if the lifetime is more than 5×107 yr.

New outlook on the possible existence of superheavy elements in nature

A consistent interpretation is given to some previously unexplained phenomena seen in nature in terms of the recently discovered long-lived high spin super- and hyper-deformed isomeric states. The Po halos seen in mica are interpreted as due to the existence of such isomeric states in corresponding Po or nearby nuclei which eventually decay by gamma- or beta-decay to the ground states of 210Po, 214Po and 218Po nuclei. The low-energy 4.5 MeV alpha-particle group observed in several minerals is interpreted as due to a very enhanced alpha transition from the third minimum of the potential-energy surface in a superheavy nucleus with atomic number Z=108 (Hs) and atomic mass number around 271 to the corresponding minimum in the daughter.

Radiochemical Investigations at the FLNR

The paper considers a programme of development of radiochemical investigations at the FLNR in the light of recent results on the synthesis of isotopes of elements 108–116 in reactions between Ca and U, Pu, Pu, Cm. Three main lines of the investigation are discussed: chemical identification and study of chemical properties of superheavy elements (SHE), on-line mass separation for the detection of SHE, and the setting of new experiments on the search of SHE in Nature.

Attempts in search for superheavy elements in nature II

The search for superheavy elements is continued. We chose minerals for long — time exposure in a sandwich arrangement (PAD[polyallyldiglycol carbonate] and mica). In a first step we investigated samples of mangenese concretions from the Pacific Ocean, enriched samples from Salton Sea and a volatile by product — fraction of copper — shale (Kupferschiefer) from Mansfeld (,,Theisenschlamm“). After an exposure time of 535 days or 326 days, respectively, and proper etching, the SSNTD's were scanned using an optical microscope. Tracks due to the fission fragments could be seen neither at the PAD nor at the mica surface. The most hopeful sample ,,Theisenschlamm“ gives about 1.2 × 10 6 tracks of α — particles at PAD. This can be explained by the uranium content. The exposure will be continued and other samples will be investigated, too.

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.

Calculation of β-delayed fission rates of neutron-rich nuclei far off stability

Beta-delayed fission branching ratios P βdf of heavy nuclides in the range 75< Z <100 and 140 ⩽ N ⩽ 184 are calculated using β-transition matrix elements determined in a pnQRPA approach. These P βdf values are of great interest for the element synthesis in the astrophysical r-process. One of the main conclusions is that β-delayed fission prevents the synthesis of superheavy elements in nature by the r-process. Implications of the results on the yields of β-stable nuclides obtained in thermonuclear explosions are discussed.

Search for Superheavy Elements in the Nature

The existence of relatively stable elements beyond the present Periodic Table is predicted by various theoretical calculations. Considering all experiments of the search for superheavy elements (SHE) in nature and their non definite positive results further search seems to be pessimistic. Nevertheless in this work the scientific necessity to continue the search in nature by a modified manner using industrial enrichment steps is pointed out.

Search for high energy alpha emitters in monazite minerals

We have attempted to find evidence for high energy alpha particles from Malaysian, Madagascan and Indian monazite minerals (rare earth and actinide phosphates) which might indicate the presence of naturally occurring superheavy elements in nature. A silicon surface barrier detector was used to detect alpha particles in conjunction with a cosmic-ray anti-coincidence detector. The results are consistent with no alphas above 12.5 MeV. This agrees with results of Fireman and Brandt 1978 but does not agree with results of Chevalier et al. 1978.

The physical and chemical aspects of the search for superheavy elements

Abstract