Nuclear chemistry

Spectroscopy of element 115 decay chains

The full document is not yet published but a paper accepted 7 Aug 2013 entitled Spectroscopy of element 115 decay chains by D. Rudolph et al. provides additional evidence for element 115:

A high-resolution $\alpha$, $X$-ray and $\gamma$-ray coincidence spectroscopy experiment was conducted at the GSI Helmholtzzentrum f\"ur Schwerionenforschung. Thirty correlated $\alpha$-decay chains were detected following the fusion-evaporation reaction $^{48}$Ca~+~$^{243}$Am. The observations are consistent with previous assignments of similar decay chains to originate from element $Z=115$. For the first time, precise spectroscopy allows the derivation of excitation schemes of isotopes along the decay chains starting with elements $Z>112$. Comprehensive Monte-Carlo simulations accompany the data analysis. Nuclear structure models provide a first level interpretation.

Search for element 113 concluded at last?

Press release from RIKEN Nishina Center for Accelerator-Based Science

The most unambiguous data to date on the elusive 113th atomic element has been obtained by researchers at the RIKEN Nishina Center for Accelerator-based Science (RNC). A chain of six consecutive alpha decays, produced in experiments at the RIKEN Radioisotope Beam Factory (RIBF), conclusively identifies the element through connections to well-known daughter nuclides. The groundbreaking result, reported in the Journal of Physical Society of Japan, sets the stage for Japan to claim naming rights for the element.

Steps in chain of decays from element 113 to mendelevium-254
The search for superheavy elements is a difficult and painstaking process. Such elements do not occur in nature and must be produced through experiments involving nuclear reactors or particle accelerators, via processes of nuclear fusion or neutron absorption. Since the first such element was discovered in 1940, the United States, Russia and Germany have competed to synthesize more of them. Elements 93 to 103 were discovered by the Americans, elements 104 to 106 by the Russians and the Americans, elements 107 to 112 by the Germans, and the two most recently named elements, 114 and 116, by cooperative work of the Russians and Americans.

With their latest findings, associate chief scientist Kosuke Morita and his team at the RNC are set follow in these footsteps and make Japan the first country in Asia to name an atomic element. For many years Morita's team has conducted experiments at the RIKEN Linear Accelerator Facility in Wako, near Tokyo, in search of the element, using a custom-built gas-filled recoil ion separator (GARIS) coupled to a position-sensitive semiconductor detector to identify reaction products. On August 12th those experiments bore fruit: zinc ions travelling at 10% the speed of light collided with a thin bismuth layer to produce a very heavy ion followed by a chain of six consecutive alpha decays identified as products of an isotope of the 113th element (Figure 1).

While the team also detected element 113 in experiments conducted in 2004 and 2005, earlier results identified only four decay events followed by the spontaneous fission of dubnium-262 (element 105). In addition to spontaneous fission, the isotope dubnium-262 is known to also decay via alpha decay, but this was not observed, and naming rights were not granted since the final products were not well known nuclides at the time. The decay chain detected in the latest experiments, however, takes the alternative alpha decay route, with data indicating that Dubnium decayed into lawrencium-258 (element 103) and finally into mendelevium-254 (element 101). The decay of dubnium-262 to lawrencium-258 is well known and provides unambiguous proof that element 113 is the origin of the chain.

Combined with their earlier experimental results, the team's groundbreaking discovery of the six-step alpha decay chain promises to clinch their claim to naming rights for the 113th element.

"For over 9 years, we have been searching for data conclusively identifying element 113, and now that at last we have it, it feels like a great weight has been lifted from our shoulders," Morita said. "I would like to thank all the researchers and staff involved in this momentous result, who persevered with the belief that one day, 113 would be ours. For our next challenge, we look to the uncharted territory of element 119 and beyond."

Element number 114: flerovium (symbol Fl) and element number 116: livermorium (symbol Lv)

The International Union of Pure and Applied Chemistry (IUPAC) has recommended names for elements 114 and 116. Scientists from the Lawrence Livermore National Laboratory (LLNL) and at Dubna proposed the names as Flerovium for element 114 and Livermorium for element 116.

Flerovium (atomic symbol Fl) was chosen to honor Flerov Laboratory of Nuclear Reactions, where superheavy elements, including element 114, were synthesized. Georgiy N. Flerov (1913-1990) was a renowned physicist who discovered the spontaneous fission of uranium and was a pioneer in heavy-ion physics. He is the founder of the Joint Institute for Nuclear Research. In 1991, the laboratory was named after Flerov - Flerov Laboratory of Nuclear Reactions (FLNR).

Livermorium (atomic symbol Lv) was chosen to honor Lawrence Livermore National Laboratory (LLNL) and the city of Livermore, Calif. A group of researchers from the Laboratory, along with scientists at the Flerov Laboratory of Nuclear Reactions, participated in the work carried out in Dubna on the synthesis of superheavy elements, including element 116. (Lawrencium -- Element 103 -- was already named for LLNL's founder E.O. Lawrence.)

In 1989, Flerov and Ken Hulet (1926-2010) of LLNL established collaboration between scientists at LLNL and scientists at FLNR; one of the results of this long-standing collaboration was the synthesis of elements 114 and 116.

The creation of elements 116 and 114 involved smashing calcium ions (with 20 protons each) into a curium target (96 protons) to create element 116. Element 116 decayed almost immediately into element 114. The scientists also created element 114 separately by replacing curium with a plutonium target (94 protons).

The creation of elements 114 and 116 generate hope that the team is on its way to the "island of stability," an area of the periodic table in which new heavy elements would be stable or last long enough for applications to be found.

The new names were submitted to the IUPAC in late October. The new names will not be official until about five months from now when the public comment period is over.

Discovery of the Elements with Atomic Number 114 and 116

A news reports from IUPAC indicates the confirmation of the discoveries of elements 114 and 116. Proposals for the names of the two elements will follow in due course:

News: Discovery of the Elements with Atomic Number 114 and 116

Priority for the discovery of the elements with atomic number 114 and 116 has been assigned, in accordance with the agreed criteria, to collaborative work between scientists from the Joint Institute for Nuclear Research in Dubna, Russia and from Lawrence Livermore, California, USA (the Dubna-Livermore collaborations). The discovery evidences were recently reviewed and recognized by a IUPAC/IUPAP joint working party. IUPAC confirmed the recognition of the elements in a letter to the leaders of the collaboration.

The IUPAC/IUPAP Joint Working Party (JWP) on the priority of claims to the discovery of new elements has reviewed the relevant literature pertaining to several claims. In accordance with the criteria for the discovery of elements previously established by the 1992 IUPAC/IUPAP Transfermium Working Group, and reiterated by the 1999 and 2003 IUPAC/IUPAP JWPs, it was concluded that “the establishment of the identity of the isotope 283Cn by a large number of decaying chains, originating from a variety of production pathways essentially triangulating its A,Z character enables that nuclide’s use in unequivocally recognizing higher-Z isotopes that are observed to decay through it.” From 2004 Dubna-Livermore collaborations the JWP notes: (i) the internal redundancy and extended decay chain sequence for identification of Z = 287114 from 48Ca + 242Pu fusion (Oganessian et al. Eur. Phys. J. A 19, 3 (2004) and Phys. Rev. C 70, 064609 (2004)); and (ii) that the report of the production of 291116 from the fusion of 48Ca with 245Cm is supported by extended decay chains that include, again, 283Cn and descendants (Oganessian et al. Phys. Rev. C 69, 054607 (2004)). It recommends that the Dubna-Livermore collaborations be credited with discovery of these two new elements.

A full synopsis of the relevant experiments and related efforts is presented in a technical report published online in Pure and Applied Chemistry on 1 June 2011. With the priority for the discovery established, the scientists from the Dubna-Livermore collaborations are invited to propose a name for the two super-heavy elements, elements 114 and 116. The suggested names will then go through a review process before adoption by the IUPAC Council.

Review of the claims associated with elements 113, 115, and 118 are at this time not conclusive and evidences have not met the criteria for discovery.

Synthesis of a New Element with Atomic Number Z=117

The discovery of a new chemical element with atomic number Z=117 is reported. The isotopes 293117 and 294117 were produced in fusion reactions between 48Ca and 249Bk. Decay chains involving 11 new nuclei were identified by means of the Dubna gas-filled recoil separator. The measured decay properties show a strong rise of stability for heavier isotopes with Z≥111, validating the concept of the long sought island of enhanced stability for superheavy nuclei.

Synthesis of a New Element with Atomic Number Z=117, Oganessian, Yu. Ts., Abdullin Sh. F., Bailey P. D., Benker D. E., Bennett M. E., Dmitriev S. N., Ezold J. G., Hamilton J. H., Henderson R. A., Itkis M. G., et al. , Phys. Rev. Lett., Apr/2010, Volume 104, Number 14, p.142502, (2010)

Synthesis of a new element with atomic number Z=117

A paper has just been accepted (5 April 2010) for publication in Physical Review Letters.1

International team discovers element 117

A new chemical element has been added to the Periodic Table: A paper on the discovery of element 117 has been accepted for publication in Physical Review Letters.

Oak Ridge National Laboratory is part of a team that includes the Joint Institute of Nuclear Research (Dubna, Russia), the Research Institute for Advanced Reactors (Dimitrovgrad), Lawrence Livermore National Laboratory, Vanderbilt University and the University of Nevada Las Vegas. ORNL's role included production of the berkelium-249 isotope necessary for the target, which was subjected to an extended, months-long run at the heavy ion accelerator facility at Dubna, Russia.

"Without the berkelium target, there could have been no experiment," says ORNL Director of Strategic Capabilities Jim Roberto, who is a principal author on the PRL paper and who helped initiate the experiment. The berkelium was produced at the High Flux Isotope Reactor and processed at the adjoining Radiochemical Engineering & Development Laboratory as part of the most recent campaign to produce californium-252, a radioisotope widely used in industry and medicine.

"Russia had proposed this experiment in 2004, but since we had no californium production at the time, we couldn't supply the berkelium. With the initiation of californium production in 2008, we were able to implement a collaboration," Roberto says.
Professor Joe Hamilton of Vanderbilt University (who helped establish the Joint Institute for Heavy Ion Research at ORNL) introduced Roberto to Yuri Oganessian of Russia's JINR. Five months of the Dubna JINR U400 accelerator's calcium-48 beam - one of the world's most powerful - was dedicated to the project.

The massive effort identified a total of six atoms of element 117 and the critical reams of data that substantiate their existence.
The two-year experimental campaign began with a 250-day irradiation in HFIR, producing 22 milligrams of berkelium-249, which has a 320-day half-life. The irradiation was followed by 90 days of processing at REDC to separate and purify the berkelium. The Bk-249 target was prepared at Dimitrovgrad and then bombarded for 150 days at the Dubna facility. Lawrence Livermore, which now has been involved in the discovery of six elements with Dubna (113, 114, 115, 116, 117, and 118), contributed data analysis, and the entire team was involved in the assessment of the results.

This is the second element that ORNL has had a role in discovering, joining element 61, promethium, which was discovered at the Graphite Reactor during the Manhattan project and reported in 1946. ORNL, by way of its production of radioisotopes for research, has contributed to the discovery of a total of seven new elements.

Members of the ORNL team include the Physics Division's Krzysztof Rykaczewsi, Porter Bailey of the Nonreactor Nuclear Facilities Division, and Dennis Benker, Julie Ezold, Curtis Porter and Frank Riley of the Nuclear S&T Division. Roberto says the success of the element-117 campaign underscores the value of international collaborations in science.
"This use of ORNL isotopes and Russian accelerators is a tremendous example of the value of working together," he says. "The 117 experiment paired one of the world's leading research reactors--capable of producing the berkelium target material--with the exceptional heavy ion accelerator and detection capabilities at Dubna."

Islands of Stability

Roberto also says the experiment, in addition to discovering a new chemical element, has pushed the Periodic Table further into the neutron-rich regime for heaviest elements. "New isotopes observed in these experiments continue a trend toward higher lifetimes for increased neutron numbers, providing evidence for the proposed "island of stability" for super-heavy nuclei," he says. "Because the half-lives are getting longer, there is potential to study the chemistry of these nuclei," Roberto says. "These experiments and discoveries essentially open new frontiers of chemistry."

—Bill Cabage

The news about the claim was announced in a press release from the Oak Ridge National Laboratory.

Tantalising news about element 117

Notes from the 31st meeting of PAC for Nuclear Physics seems to suggest that a claim for element 117 (at the base of the halogen column) may come in the coming weeks and months. It's not very clear which isotopes may have been formed so watch this space.

IV. Experiments on the synthesis of element 117
The PAC heard with great interest the report on the results of the experiment dedicated to the synthesis of element 117 in the 48Ca + 249Bk reaction. The PAC congratulates the staff of the Flerov Laboratory on the discovery of element 117 and new isotopes of elements 115, 113, 111, 109, 107, and 105. The discovery of chains of two neighboring isotopes emphasizes the importance of the odd-even and odd-odd effect for such heavy nuclei. It is in fact especially interesting that the odd-odd chain (3n channel) neighboring to the odd-even chain (4n channel) is twice longer (6 α particles).

Copernicium confirmed as name of element 112

IUPAC has officially approved the name copernicium, with symbol Cn, for the element of atomic number 112. Priority for the discovery of this element was assigned, in accordance with the agreed criteria, to the Gesellschaft für Schwerionenforschung (GSI) (Center for Heavy Ion Research) in Darmstadt, Germany. The team at GSI proposed the name copernicium which has now been approved by IUPAC. Sigurd Hofmann , leader of the GSI team stated that the intent was to "salute an influential scientist who didn't receive any accolades in his own lifetime, and highlight the link between astronomy and the field of nuclear chemistry."

The name proposed by the Gesselschaft für Schwerionenforschung (GSI) lies within the long tradition of naming elements to honor famous scientists. Nicolaus Copernicus was born on 19 February 1473, in Torún, Poland and died on 24 May 1543, in Frombork/Frauenburg also in Poland. His work has been of exceptional influence on the philosophical and political thinking of mankind and on the rise of modern science based on experimental results. During his time as a canon of the Cathedral in Frauenburg, Copernicus spent many years developing a conclusive model for complex astronomical observations of the movements of the sun, moon, planets and stars. His work published as “De revolutionibus orbium coelestium, liber sixtus” in 1543 had very far reaching consequences. Indeed the Copernican model demanded major changes in the view of the world related to astronomy and physical forces and well as having theological and political consequences. The planetary system introduced by Copernicus has been applied to other analogous systems in which objects move under the influence of a force directed towards a common centre. Notably, on a microscopic scale this is the Bohr model of the atom with its nucleus and orbiting electrons.

The Recommendations will be published in the March issue of the IUPAC journal Pure and Applied Chemistry and is available online at Pure Appl. Chem., 2010, Vol. 82, No. 3, pp. pp 753-755 (doi: 10.1351/PAC-REC-09-08-20)

Approaches to element 120 (unbinilium)

Attempts have been made at GSI to make element 120 (unbinilium). Several new elements have been made at GSI in the last few years. However after 120 days no decay chain of element 120 was found. With the total number of 2.6 × 1019 projectiles which impinged upon the target, it deduced that the stability in the region around Z=120, N=184 is not exceptionally high with respect to the neighbouring regions.

Currently it is not clear what proton number defines the location of the "island of stability". Various theoretical models suggest numbers of Z=114, 120 or 126. Workers at GSI investigated the element Z=120 (element 120, containing 120 protons within the nucleus). Three different projectile-target combinations all lead to the same compound nucleus 302120 or 302Ubn

  • 64Ni + 238U
  • 58Fe + 244Pu, and
  • 54Cr + 248Cm

The neutron number of the compound nucleus 302120 is N=182. This is only 2 neutrons below N=184 where the neutron shell closure is expected. Therefore, 302120 or 302Ubn is closer to the N=184 shell than any other so far produced compound nucleus with lower Z.

The largest production rate for Z=120 is predicted for the most mass asymmetric projectile/target combination 54Cr + 248Cm. However, at SHIP this experiment was not possible so the reaction 64Ni + 238U was studied. If the proton shell closure is at Z=120 then an enhanced production rate and half-live of the element 120 would be expected. Depending on the magnitude of the stabilization due to the closed shell, one could expect up to a few events per week for the isotopes 299120 and 298120 produced in 64Ni + 238U reactions. The half-lives are expected to be of the order of some 10 μs, but in the end no luck, this time at least.

Energy dependence of 209-Bi fragmentation in relativistic nuclear collisions

The results of cross-section measurements for the reactions 209Bi(12C,X)Au, E=4.8 and 25.2 GeV and 209Bi(20Ne,X)Au, E=8.0 GeV are reported. The observed yields of the gold isotopes show a similar dependence on mass number for each reaction, differing slightly in the position of the centroid of the distribution. As the projectile energy increases, the inferred excitation energy of the primary residues remains the same or decreases slightly. This observation is in agreement with the predictions of the intranuclear cascade model of relativistic heavy ion collisions.

NUCLEAR REACTIONS 209Bi(12C,X)Au, E=4.8,25.2 GeV; 209Bi(20Ne,X)Au, E=8.0 GeV; measured Au isotopic distributions, relativistic heavy ions, target fragmentation, Ge(Li) spectroscopy.

Energy dependence of 209-Bi fragmentation in relativistic nuclear collisions, Aleklett, K., Morrissey D., Loveland W., McGaughey P., and Seaborg G. , Physical Review C, 3/1981, Volume 23, Issue 3, p.1044 - 1046, (1981)

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