News & Dates

March 29, 2021

We mourn

              Maximilian Rapps (1986 - 2021)

who passed away unexpectedly last week.
He designed, built, and commissioned a spin coater for the fabrication of thin films for nuclear chemical applications in our group as part of his master's thesis and fabricated and characterized first samples.
Max's cheerful nature, brimming with ideas, his creativity, his scientific expertise as well as his manual skills were a great asset to our group.
He is greatly missed. 
             Ch. Düllmann          
Maximillian Rapps

February 15, 2021

Probing precipitation properties of Rutherfordium

Superheavy elements are short-lived and only available on a single-atom level, making their chemical properties very challenging to study. Now, through their co-precipitation with samarium, single atoms of rutherfordium have been shown to form hydroxide complexes but not ammine ones.

A News&Views article to this topic was published recently by Nature Chemistry:
A. Yakushev
Probing precipitation properties
Nat. Chem. (2021)
DOI: 10.1038/s41557-020-00625-7

This publikation is devoted to the original experimental work on Rf precipitation study, performed at RIKEN (Japan).
Details to this work are available in the article by Yoshitaka Kasamatsu et. al, published in the same issue of Nature Chemistry.

Kasamatsu, Y., Toyomura, K., Haba, H. et al.
Co-precipitation behaviour of single atoms of rutherfordium in basic solutions
Nat. Chem. (2021)
DOI: 10.1038/s41557-020-00634-6

Joint press release of GSI Helmholtzzentrum für Schwerionenforschung, Helmholtz Institute Mainz, Johannes Gutenberg University Mainz, in collaboration with Lund University

January 25, 2021

Change of course on the journey to the island of stability

Center of the island of stability is not located at element 114 — Heavier elements will move into the spotlight

An international research team succeeded in gaining new insights into the artificially produced superheavy element flerovium, element 114, at the accelerator facilities of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Under the leadership of Lund University in Sweden and with significant participation of Johannes Gutenberg University Mainz (JGU) as well as the Helmholtz Institute Mainz (HIM) in Germany and other partners, flerovium was produced and investigated to determine whether it has a closed proton shell. The results suggest that, contrary to expectations, flerovium is not a so-called "magic nucleus". The results were published in the journal Physical Review Letters and additionally highlighted with a synopsis by the American Physical Society..

In the late 1960s, Sven-Gösta Nilsson, then a physics professor at Lund University, and others formulated a theory about the possible existence of still unknown superheavy elements. In the meantime, such elements have been created and many predictions have been confirmed. The discovery of the six new elements 107 to 112 was achieved at GSI in Darmstadt, and further ones up to element 118 are now known as well. Strongly increased half-lives for the superheavy elements due to a "magic" combination of protons and neutrons were also predicted. This occurs when the shells in the nucleus, each holding a certain number of protons and neutrons, are completely filled. "Flerovium, element 114, was also predicted to have such a completed, 'magic' proton shell structure. If this were true, flerovium would lie at the center of the so-called 'island of stability’, an area of the chart of nuclides where the superheavy elements should have particularly long lifetimes due to the shell closures," explains Professor Dirk Rudolph of Lund University, who is the spokesperson of the international experiment.

The TASCA recoil separator at GSI Darmstadt.
The calcium beam from the UNILAC accelerator passed through the beamline visible on the left of the image to the target area (center of image) where nuclear fusion leading to flerovium production took place. The nuclear reaction products and the unreacted calcium beam then passed through the magnets visible in red on the right, which isolated the flerovium nuclei from all other particles. Flerovium then entered the detection apparatus at the end of the separator.
Photo/©: Gabi Otto/GSI
    Detector setup of Lund
Detector setup of Lund University.
By means of a silicon detector system inside a vacuum chamber surrounded by new germanium detectors, the energy and time of arrival of the flerovium nuclei and their decay products, e.g. alpha particles, electrons or fission products, as well as X-rays and gamma rays,
were registered.
Photo/©: Anton Såmark-Roth/Univ. Lund
Atomic nuclei of flerovium show unusual decay channels

Nilsson's theories inspired the international collaboration led by the Lund group to investigate whether flerovium nuclei indeed exhibit the predicted magical properties. Their experiments, performed at the UNILAC accelerator at GSI in Darmstadt in the framework of the FAIR Phase 0 experimental program, lasted 18 days. Every second, four trillion calcium-48 nuclei with 20 protons were accelerated to ten percent of the speed of light. They irradiated a thin foil containing rare plutonium-244 with 94 protons to produce atomic nuclei of flerovium, which has 114 protons, by nuclear fusion. This so-called target was produced at the Department of Chemistry at JGU, using, plutonium provided, among others, by the Lawrence Livermore National Laboratory, USA. Strong magnets of the GSI recoil separator TASCA separated the flerovium nuclei from the intense calcium ion beam; subsequently they were registered in a detector setup specifically developed in Lund for this experiment.

The detector measured the radioactive decay of 30 flerovium nuclei — i.e., the emission of nuclear fragments of flerovium — with high efficiency and accuracy. By precisely analyzing these fragments and their emission times, the team was able to determine unusual decay channels of flerovium nuclei that could not be reconciled with its originally predicted "magical" properties. "Our study shows that element 114 is no more stable than others in its vicinity. This is a very important piece of the puzzle in the continued search for the center of the coveted island of stability," said Professor Christoph Düllmann, professor of nuclear chemistry at JGU and head of the research groups at GSI and HIM.

The new results will be of great benefit to science. Instead of continuing to search for the center of the island of stability in the region of element 114, even heavier ones like the as yet undiscovered element 120, will now move into the spotlight.

This press release as pdf-file

More Info:

December 28, 2020

"pro-physik" lists two highlights from our group in its 2020 annual review

The discovery of the new isotope mendelevium-244 at TASCA and the ultra-precise measurement of the mass of the deuteron, for which our group provided the deuterium-target are listed in the annual review 2020 of "pro-physik" in particle, nuclear and accelerator physics.

November 16, 2020

Laser-induced protons used for the first time for nuclear reactions

Detection of the reaction products by technology, from the field of superheavy elements

A collaboration between the research departments plasma physics and SHE chemistry at GSI succeeded in generating protons by bombarding thin targets with short pulses (500 fs) of the high-intensity PHELIX laser (200 J), which in turn were used for the first time to induce a nuclear reaction, by irradiating uranium-238. This process produced, among others, the volatile fission fragments iodine and xenon, which were transported from the target chamber to an activated carbon filter by means of a fast gas-jet transport as it is often used in the chemical study of superheavy elements. The fragments‘ decay was registered with a germanium detector. This collaboration is a good example of synergies between widely differing fields of research at GSI - in this case plasma physics and nuclear chemistry
The results were published in Scientific Reports of the journal Nature (see below).


November 10, 2020

2020 Nernst-Haber-Bodenstein-Prize for PD Dr. Stefan Knecht

PD Dr. Stefan Knecht was awarded the 2020 Nernst-Haber-Bodenstein-Prize of the German Bunsengesellschaft for Physical Chemistry in recognition of his scientific achievements to the fundamental developments of efficient multi configurational ab initio theories that can be universally applied to electron structure problems for molecules composed of any elements of the periodic table. The "Nernst-Haber-Bodenstein Prize" is awarded annually to young scientists who have distinguished themselves through experimental or theoretical work.
The DBG award ceremony was held online for the first time.

October 28, 2020

Mainz University and GSI to play an important role in the EU-funded network of doctoral students for research on radioactive elements

Nuclear and atomic physicists and nuclear chemists of Mainz University and GSI are closely involved in the EU Innovative Training Network on Laser Ionization and Spectroscopy of Actinide Elements
Joint press release by GSI, HIM and JGU


Doctoral student Jessica Warbinek (right) together with her supervisor, Professor Michael Block (left) working on the optimization of a vacuum chamber, which she will subsequently use for her work during the upcoming experimental phase at GSI
Copyright: Jutta Leroudier, GSI Helmholtzzentrum

In the context of an international network funded by the European Union, scientists at Johannes Gutenberg University Mainz (JGU) and GSI Helmholtzzentrum für Schwerionenforschung (GSI) are participating in the education of young postgraduate students in the fields of nuclear and atomic physics and nuclear chemistry. The goal of this Innovative Training Network (ITN) on Laser Ionization and Spectroscopy of Actinide Elements (LISA) is to decipher the structure of actinides, i.e., the heavy, mostly short-lived elements at the bottom of the periodic table, and thus put in place the prerequisite for their future use in biomedical physics, in nuclear applications, and for environmental monitoring. Members of the consortium are some of the world's leading experts in fundamental atomic and nuclear physics and nuclear chemistry. The EU is supporting the LISA project for a period of four years with a total funding worth EUR 4 million.

More info ...


Actinides in the periodic table of the elements.
Copyright: GSI Helmholtzzentrum

October 09, 2020

The new heavy isotope mendelevium-244 and a puzzling short-lived fission activity

Gaining a better understanding of the limiting factors for the existence of stable, superheavy elements is a decade-old quest of chemistry and physics. Superheavy elements, as are called the chemical elements with atomic numbers greater than 103, do not occur in nature and are produced artificially with particle accelerators. They vanish within seconds. A team of scientists from GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Johannes Gutenberg University Mainz (JGU), the Helmholtz Institute in Mainz (HIM), and the University of Jyväskylä, Finland, led by Dr. Jadambaa Khuyagbaatar from GSI and HIM, has provided new insights into the fission processes in those exotic nuclei and for this, has produced the hitherto unknown nucleus mendelevium-244. The experiments were part of "FAIR Phase 0", the first stage of the FAIR experimental program. The results have now been published in the journal "Physical Review Letters".


Cut out of the chart of nuclei in the region of the mendelevium nuclei. Each box represents an atomic nucleus, with the numbers of protons increasing in the vertical direction and the numbers of neutrons in the horizontal direction. Known nuclei are shown by colored boxes, where the color indicates the nuclear decay mode: alpha decay (yellow), beta decay (brown), spontaneous fission (green). Thick-framed boxes indicate odd-odd nuclei, in which beta-delayed fission has been predicted to occur with >1 % probability among all beta decays (data taken from J. Khuyagbaatar, Eur. Phys. J. A 55, 134 (2019)). The probabilities are indicated in blue. The location and decay properties of the new isotope mendelevium-244 are highlighted.
Picture: J. Khuyagbaatar, GSI

The leader of the experiment, Dr. Jadambaa Khuyagbaatar standing in the experimental hall X8 in front of the TASCA separator used in the mendelevium-244 experiment.
Photo: A. Di Nitto

Focal plane detector of the TASCA separator, into which the mendelium-244 isotope was implanted and its decay registered.
Photo: A. Yakushev, GSI

Heavy and superheavy nuclei are increasingly unstable against the fission process, in which the nucleus splits into two lighter fragments. This is due to the ever-stronger Coulomb repulsion between the large number of positively charged protons in such nuclei, and is one of the main limitations for the existence of stable superheavy nuclei.

The nuclear fission process was discovered more than 80 years ago and is being studied intensely to this day. Most experimental data on the spontaneous fission are for nuclei with even numbers of protons and neutrons – called “even-even nuclei”. Even-even nuclei consist entirely of proton and neutron pairs and their fission properties are rather well describable by theoretical models. In nuclei with an odd number of either neutrons or protons, a hindrance of the fission process when compared to the properties of even-even nuclei has been observed and traced back to the influence of such a single, unpaired constituent in the nucleus.

However, the fission hindrance in “odd-odd nuclei”, containing both, an odd number of protons and an odd number of neutrons, is less well known. Available experimental data indicate that the spontaneous fission process in such nuclei is greatly hindered, even more so than in nuclei with only one odd-numbered type of constituents.

Once the fission probability is most reduced, other radioactive decay modes like alpha decay or beta decay become probable. In beta decay, one proton transforms into a neutron (or vice versa) and, accordingly, odd-odd nuclei turn into even-even nuclei, which typically have a high fission probability. Accordingly, if a fission activity is observed in experiments on the production of an odd-odd nucleus, it is often difficult to identify whether fission occurred in the odd-odd nucleus, or not rather started from the even-even beta-decay daughter, which can then undergo beta-delayed fission. Recently, Dr. Jadambaa Khuyagbaatar from GSI and HIM predicted that this beta-delayed fission process may be very relevant for the heaviest nuclei and – in fact – may be one of the main decay modes of beta-decaying superheavy nuclei.

More info ...


J. Khuyagbaatar1,2,*, H. M. Albers2, M. Block1,2,3, H. Brand2, R. A. Cantemir2, A. Di Nitto3, Ch. E. Düllmann1,2,3, M. Götz1,2,3, S. Götz1,2,3, F. P. Heßberger1,2, E. Jäger2, B. Kindler2, J. V. Kratz3, J. Krier2, N. Kurz2, B. Lommel2, L. Lens2,3, A. Mistry2, B. Schausten2, J. Uusitalo4, A. Yakushev2
Search for Electron-Capture Delayed Fission in the New Isotope 244Md
Physical Review Letters 125, 142504 (2020)
DOI: 10.1103/PhysRevLett.125.142504
*Corresponding author

Involved Institutes
  1. Helmholtz Institute Mainz (HIM), Mainz, Germany
  2. GSI Helmholzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
  3. Johannes Gutenberg University Mainz, Mainz, Germany
  4. University of Jyväskylä, Jyväskylä, Finland

Joint Press Release of the Helmholtz Institute Mainz, the GSI Helmholtzzentrum für Schwerionenforschung GmbH, the Johannes Gutenberg University Mainz, and the University of Jyväskylä

October 06, 2020

Hunting for the lowest known nuclear-excited state

Measurements in thorium-229 take a step towards the direct laser excitation of an atomic nucleus in this unique isotope

Nuclear clocks could make our time measurement even more accurate than atomic clocks. The key to this lies in thorium-229, an atomic nucleus whose lowest excited state has very low energy. A research team from the Kirchhoff-Institute of Physics at the University of Heidelberg, the Vienna University of Technology (TU-Wien), the Johannes Gutenberg University Mainz (JGU), the Helmholtz Institute in Mainz (HIM), and the GSI Helmholtzzentrum in Darmstadt has now succeeded in measuring this low energy. Using an extremely accurate detector, it was possible to detect the tiny temperature increase due to the energy released during the de-excitation of the atomic nucleus. This brings the realization of a nuclear clock a big step closer.

In radioactive decay, atomic nuclei spontaneously re-arrange, eject some part of their building blocks, and transform into a nucleus of a different atom. In this process, the new "daughter atom” usually has internally stored energy that is released in the form of gamma rays. The energies of these rays are characteristic for each type of nucleus – just like fingerprints. Researchers learn a lot about atomic nuclei by characterizing these gamma-ray fingerprints.

Back in 1976, L.A. Kroger and C.W. Reich investigated the decay of uranium-233, which is an artificial nucleus of uranium that decays to thorium-229 by emitting an alpha-particle; this is immediately followed by the emission of characteristic gamma-rays that occur in distinct and generally well-understood patterns. Kroger and Reich, however, registered an anomaly: one gamma-ray that was predicted by all nuclear theories was missing in the measured signals. The best explanation was that the internal energy stored in the lowest nuclear excitation of thorium-229 was too low to be observed by the detectors. Over the following decades, many attempts were made to observe this low-energy gamma-ray without success, constraining it to ever-lower energies.

New perspectives for constructing a nuclear clock

Nowadays, we know that the lowest excited-energy state of the thorium-229 nucleus, called an isomer state, is located at the lowest known energy among all nuclei, at an energy that is orders of magnitudes lower than usual excitation energies. Consequently, the energy of the associated gamma-ray is so low that it is placed in the ultraviolet region of the electromagnetic spectrum rather than in the typical gamma-ray region. This leads to the unique situation that the opposite process of the de-excitation by the emission of this "ultraviolet gamma-ray", namely the excitation of the lower state is possible by shining ultraviolet light onto the nucleus. It is the only nuclear system that could be excited with "table-top" laser light. This opens up exciting prospects, including the construction of a "nuclear" clock, in which time is measured by oscillations of the nucleus between these two states. The precision of such a clock is predicted to be better than that of the best current atomic clocks, which rely on oscillations between states in the electron shell, which is more susceptible to external perturbations than the 10.000 times smaller nucleus.

The key problem is, though, that the energy of the isomer state is not yet known with sufficient precision to know which ultraviolet light is needed to stimulate the oscillation. A consortium of researchers from Heidelberg, Vienna, Mainz, and Darmstadt have now repeated the iconic gamma spectroscopy measurement of Kroger and Reich, but using a highly advanced state-of-the-art gamma spectrometer, designed explicitly for registering rays of such low energy.

Cool studies give the highest precision

For this, the research team of Professor Christian Enss and Dr. Andreas Fleischmann at the Kirchhoff-Institute for Physics of the University of Heidelberg developed a magnetic microcalorimeter named maXs30. This detector is cooled to minus 273 degrees Celsius and measures the minuscule temperature rise that occurs when a gamma-ray is absorbed. The temperature increase leads to a change in the detector's magnetic properties, which is then converted into an electric signal using SQUID magnetometers similar to those that are commonly used in magnetic resonance tomography. The maXs30 detector has unprecedented energy resolution and gain linearity; still, it took about 12 weeks of continuous measurement to obtain the gamma-ray spectrum with sufficient precision.

To make this challenging measurement possible, the team of Professor Christoph Düllmann in Mainz and Darmstadt produced a special sample of uranium-233. First, they chemically removed all decay daughter products that had built up over time before the sample was used. They also removed unwanted radioisotopes, the decay of which leads to an unwanted background in the measured data. Then they designed a source geometry and sample container that led to minimum interference of the weak signals on their way from the sample to the maXs30 calorimeters. These steps were required for the success of the measurement because only one in 10.000 decay processes produces a signal that is useful for the determination of the isomer energy. The measurement produced the most precise gamma-ray spectrum of the uranium-233 to thorium-229 decay to date. The team of Professor Thorsten Schumm at Vienna University of Technology, together with the Heidelberg team, employed four different schemes to derive the energy of the isomer state from this data. The most precise one yielded a value of 8.10(17) electronvolts, which corresponds to light of a wavelength of 153.1(32) nm, with the number in parentheses indicating the uncertainty of the last digits.

This measurement paves the way for a direct laser excitation of the thorium-229 isomer. The energy spectrum is openly accessible at:

8x8 array of maXs30 detectors
A false color scanning electron microscopy image of the 8x8 array of maXs30 detectors.
Credit: Matthäus Krantz


Tomas Sikorsky1,2*, Jeschua Geist1*, Daniel Hengstler1, Sebastian Kempf1, Loredana Gastaldo1, Christian Enss1, Christoph Mokry3,4, Jörg Runke3,5, Christoph E. Düllmann3,4,5, Peter Wobrauschek2, Kjeld Beeks2, Veronika Rosecker2, Johannes H. Sterba2, Georgy Kazakov2, Thorsten Schumm2, and Andreas Fleischmann1
Measurement of the 229Th Isomer Energy with a Magnetic Microcalorimeter
Physical Review Letters 125, 142503 (2020)
DOI: 10.1103/PhysRevLett.125.142503
*Corresponding author(s)

Involved Institutes
  1. Kirchhoff-Institute for Physics, Heidelberg University, Heidelberg, Germany
  2. Institute for Atomic and Subatomic Physics, TU Wien, Vienna, Austria
  3. Johannes Gutenberg Universität Mainz, Mainz
  4. Helmholtz Institute Mainz (HIM), Mainz
  5. GSI Helmholzzentrum für Schwerionenforschung GmbH, Darmstadt

Accompanying article
Ticking Toward a Nuclear Clock
Physics 13, 152 (2020)
by Lars von der Wense, JILA, University of Colorado Boulder, Boulder, USA
DOI: 10.1103/Physics.13.152

Joint Press Release of the University of Heidelberg, TU Wien, Johannes Gutenberg University Mainz, Helmholtz Institute Mainz, and GSI Helmholtzzentrum für Schwerionenforschung GmbH

September 03, 2020

Mass of the deuteron corrected

Scientists from Heidelberg, Darmstadt und Mainz publish results in „Nature“

Joint Press Release of the MPI for Nuclear Physics Heidelberg, Johannes Gutenberg University Mainz/PRISMA+ Cluster of Excellence, GSI Helmholtz Centre for Heavy Ion Research Darmstadt and Helmholtz Institute Mainz

PM Deuteron - Mainz

The deuterated thymidine (left) provided the deuterium nucleus and the hydrogen-deuterium molecule, whose masses were measured. The electron microscope image in the background shows the sample prepared for the experiment using a Drop-on-Demand technique. Both the sample preparation and the mass measurement were performed at JGU Mainz.

© Raphael Haas, Christoph Düllmann (JGU Mainz)
Trap Tower

Assembly of the LIONTRAP Penning-trap system
© Max-Planck-Institut für Kernphysik, Heidelberg

High-precision measurements of the mass of the deuteron, the nucleus of heavy hydrogen, provide new insights into the reliability of fundamental quantities in atomic and nuclear physics. This is reported in the journal "Nature" by a collaboration led by the Max Planck Institute for Nuclear Physics Heidelberg, Germany, and partners from the Johannes Gutenberg University Mainz, the GSI Helmholtz Centre for Heavy Ion Research Darmstadt and the Helmholtz Institute Mainz, Germany. Thus, data directly related to the atomic mass standard, are now available for hydrogen H, deuterium D and the molecule HD, which the scientists have also reweighed.

More Info...


Sascha Rau1*, Fabian Heiße1,2, Florian Köhler-Langes1, Sangeetha Sasidharan1,2, Raphael Haas2,3,4,5, Dennis Renisch3, 4, Christoph E. Düllmann2,3,4,5, Wolfgang Quint2,
Penning-trap mass measurements of the deuteron and the HD+ molecular ion
Nature 585, 43–47 (2020)
DOI: 10.1038/s41586-020-2628-7
*Corresponding author

Involved Institutes
  1. Max Planck Institute for Nuclear Physics, Heidelberg, Germany
  2. GSI Helmholtz Centre for Heavy Ion Research GmbH, Darmstadt, Germany
  3. Johannes Gutenberg University Mainz, Mainz, Germany
  4. Helmholtz Institute Mainz (HIM), Mainz, Germany
  5. PRISMA+ Cluster of Excellence, Johannes Gutenberg University Mainz, Mainz, Germany

Accompanying article in the category "News and Views" in Nature
Precise measurement of deuteron mass raises hopes of solving the nuclear-mass puzzle
Nature 585, 35-36 (2020)
by Jeroen C. J. Koelemeij, Dept. of Physics and Astronomy, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
DOI: 10.1038/d41586-020-02474-3

News Announcements
  • Johannes Gutenberg University Mainz, Mainz, Germany (german, english, Sept 02, 2020)
  • GSI Helmholtz Centre for Heavy Ion Research GmbH, Darmstadt, Germany (german, english, Aug. 31, 2020)
  • Max Planck Institute for Nuclear Physics, Heidelberg, Germany (german, english, Sept 02, 2020)

December 6, 2019

International Year of the Periodic Table: Closing ceremony with GSI participation

 PSE Japan

The International Year of the Periodic Table was celebrated in 2019. One highlight was the closing ceremony in Tokyo, where scientists from GSI and FAIR also participated.
Photo: Sebastian Raeder / GSI

It was the culmination of an extraordinary anniversary year: the closing ceremony of the International Year of the Periodic Table proclaimed by the United Nations, recently held in Tokyo. 2019 marks the 150th anniversary of the discovery of the periodic table. The GSI Helmholtzzentrum für Schwerionenforschung was also represented at the festive event in Japan. With its decades of successful research and the discovery of six new chemical elements, GSI contributed significantly to the updating of the periodic table. ...

More Info...

Complete Article as pdf

November 2019

"Giersch Excellence Award“ for Raphael Haas

Giersch Award 2019

The picture shows the awardee with Mrs. Senatorin E.h. Karin Giersch on occasion of the award ceremony on October 24, 2019, at FIAS in Frankfurt.
Photo: Uwe Dettmar

On November 04, 2019, Raphael Haas won a "Giersch Excellence Award", sponsored by the Stiftung Giersch for outstanding achievements within the PhD phase. Raphael Haas devised the ODIn (Off-line Deposit Irradiation) setup for off-line conditioning of nuclear targets, which is of direct relevance for the production of the superheavy elements, and for the refinement of methods to produce thin samples of exotic radionuclides serving as recoil-sources for daughter isotopes for applications in several fields of nuclear physics and chemistry.

September 12, 2019

Probing a nuclear clock transition

Physicists have measured the energy associated with the decay of a metastable state of the thorium-229 nucleus. This is a significant step on the way to a nuclear clock which will be far more precise than the best of today’s atomic timekeepers.

Modern atomic clocks are the most accurate measurement tools currently make it possible to enhance timing accuracy by another order of magnitude. Now a research team led by LMU physicist Peter Thirolf, in collaboration with colleagues at the Max Planck Institute for Nuclear Physics in Heidelberg, the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Johannes Gutenberg University Mainz, Helmholtz Institute Mainz, the University of Bonn and the Technical University of Vienna has taken an important step towards such a clock. Indeed, the new study is featured on the title page of the leading journal Nature. In the paper, the authors report that they have succeeded in quantifying the energy released by the decay of the excited thorium-229 nucleus, which is an essential prerequisite for the realization of a thorium-based nuclear clock.

Clock generators are oscillations in the atomic nucleus

Unlike current atomic clocks, which make use of oscillations in the outer electron shells of atoms, nuclear clocks employ oscillations within the nucleus as their timekeeper. In both cases, the oscillations are the product of transitions between defined energy levels, which can be excited by laser light of a specific wavelength. Typically, the energies required to excite oscillations in the vast majority of atomic nuclei are orders of magnitude higher than those required to stimulate transitions in the orbital shells of electrons – which precludes the use of conventional lasers for this purpose. However, there is only one viable candidate for the development of a nuclear clock – the thorium-229 nucleus. Its excited state is located at an energy that is by far the lowest of any state found in the approximately 3800 currently known atomic nuclei. Irradiation with UV light, which is within the capability of lasers now available, is sufficient to populate this excited state.

However, up to now, the precise energy required to generate the excited thorium-229 has remained unknown. “To induce the nuclear transition, the wavelength of the laser light must be tuned to match the transition energy exactly. We have now succeeded in measuring this precisely for the first time,” says Benedict Seiferle, lead author of the new paper.

Uranium-233 sources as suppliers of excited thorium-229

For these measurements, carried out at LMU, the authors of the study made use of the doubly charged thorium-229 cation. Sources providing this cation in the excited nuclear state were developed in Mainz. “Uranium-233 was chemically purified and subsequently deposited on titanium-covered silicon wafers using an electrochemical method. This yields homogeneous thin films. Uranium-233 undergoes alpha decay, producing thorium-229. Thorium-229 recoils from the thin film due to the energy released in the alpha decay, hence entering into a dedicated ion trap developed at LMU in which thorium-229 cations are recovered,” Christoph Düllmann, chemist at GSI Helmholtzzentrum, University Mainz and HIM, describes the process. The excited state of the cation has a lifetime of hours. This is relatively long for an excited nuclear state and is crucial for the future development of the clock, but it hampers measurement of the decay energy. “This long lifetime means that decay to the ground state occurs only rarely. As measurement of this decay was the goal of our experiment, we exploited the fact that decay occurs rapidly when the cations are given the opportunity to collect the missing electrons,” says Seiferle.

To provide electrons, Seiferle and colleagues guided the ions through a layer of graphene. On its way through this layer, each ion picks up two electrons and emerges as a neutral atom on the other side. Thanks to this controlled neutralization step, the excited state then decays to the ground state within a few microseconds. The neutralized atoms expel an electron from an outer atomic shell, thus generating a positively charged thorium-229 ion. The kinetic energy of the free electron depends on the excitation energy of the nuclear state and is determined using an electron spectrometer. However, this energy is only a fraction of the energy used to generate the excited nuclear state. The rest remains in the thorium-229, which renders the interpretation of the resulting spectra complex. To get around this problem, the authors based at the Max-Planck Institute for Theoretical Physics in Heidelberg calculated the spectra to be expected. With the aid of these predictions, and in collaboration with their colleagues in Vienna and Bonn, the team in Munich was then able to determine the energy actually associated with the decay of the excited nuclear state.

Nucleus excitation by laser beams with a wavelength of 150 nanometers possible

The result indicates that the thorium-229 nucleus can be excited to this level by irradiation with laser light at a wavelength . Now lasers specifically designed to emit in this wavelength range can be constructed. This step will bring the first nuclear clock a great deal closer to practical realization. The researchers believe that a thorium-based nuclear clock will open up new avenues in the basic sciences, but will also find many applications, which only become possible on the basis of extremely precise measurements in the time domain.

The current results opens the way for new research prospects at the FAIR accelerator facility currently being built at GSI. Professor Thomas Stöhlker, Vice Director of Research and head of the Atomic Physics division at GSI, says: „This refined energy value opens up future research opportunities at the FAIR storage rings, allowing for precision studies of thorium-229 and its isomer at highest charge states via di-electronic recombination.“

uranium-233 source
The uranium-233 source (large disk in center of image) produced at the Johannes Gutenberg University Mainz, Germany, mounted inside the experimental apparatus at the Ludwigs-Maximilian-University Munich, Germany. Components of the setup are reflected in the surface of the source.
Credit: Lars von der Wense, LMU Munich
electron spectrometer
Central part of the electron spectrometer that was used for the energy measurement of the first excited state of Thorium-229 at LMU Munich.
Credit: Benedict Seiferle, LMU


Benedict Seiferle1*, Lars von der Wense1, Pavlo V. Bilous2, Ines Amersdorffer1, Christoph Lemell3, Florian Libisch3, Simon Stellmer4, Thorsten Schumm5, Christoph E. Düllmann6,7,8, Adriana Pálffy2, & Peter G. Thirolf1
Energy of the 229Th nuclear clock transition
Nature 573, 243–246 (2019)
DOI: 10.1038/s41586-019-1533-4

*Corresponding author

Involved Institutes
  1. Ludwig-Maximilians-Universität München (LMU), Garching
  2. Max-Planck-Institut für Kernphysik, Heidelberg, Germany
  3. Institute for Theoretical Physics, TU Wien, Vienna, Austria
  4. University of Bonn, Bonn, Germany
  5. Atominstitut, TU Wien, Vienna, Austria
  6. GSI Helmholzzentrum für Schwerionenforschung GmbH, Darmstadt
  7. Helmholtz Institut Mainz (HIM), Mainz
  8. Johannes Gutenberg Universität Mainz, Mainz
News Announcements

August 25 - 30, 2019

TAN 19

Press Release GSI (download)

IUPAC and NuPECC Poster Prizes
Special Symposium "International Year of the Periodic Table"

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June 2019

Study of the mechanism that suppresses superheavy element production in cold fusion reactions

The six superheavy elements with atomic numbers 107-112 were discovered at GSI. They were produced in nuclear fusion reactions using shell-stabilized target nuclei at and around doubly-magic 208Pb. These reaction partners allow compound nuclei containing all nucleons of the projectile and target nuclei to be produced at low excitation energy. This favors their survival on the evolution to a superheavy nucleus, containing all protons of the two reaction partners. The low energy led to these reactions being termed “cold fusion reactions”. With increasing number of protons in the compound nuclei – i.e., towards ever heavier elements – the rate at which such nuclei can be produced in cold fusion reactions has been observed to decrease rapidly. Only one element beyond 112 (named copernicium) has been identified in a cold fusion reaction: element 113 (nihonium), the discovery of which at RIKEN was accepted by IUPAC in 2015. Along with nihonium, also three further even heavier elements, including elements 115 (moscovium) and 117 (tennessine) that were also studied at the TASCA separator at GSI, were accepted, thus completing the seventh row of the periodic table. Beyond nihonium, all elements were produced in reactions using doubly-magic 48Ca projectiles, reiterating the advantage of using such shell-stabilized reaction partners.

While it had been recognized decades ago that production rates in cold fusion reactions decrease steeply the heavier the fusion product is, the dynamical mechanisms underlying this trend remained only partially understood. To improve our understanding, detailed studies of three cold fusion reactions using 48Ca, 50Ti, and 54Cr projectiles on 208Pb targets, leading to the elements 102 (nobelium), 104 (rutherfordium), and 106 (seaborgium), have been performed at the Heavy Ion Accelerator Facility at the Australian National University (ANU) in Canberra, Australia, in a collaboration with scientists from GSI Darmstadt, HIM Mainz, and Johannes Gutenberg University Mainz. In contrast to the experiments at GSI, which focus on the observation of the fusion products, the present experiments aimed at studying the complementary reaction outcome – i.e., the fission-like process when projectile and target nuclei do not fuse, but reseparate a short time after coming into close contact, thus suppressing fusion. The process leads to the correlated emission of two nuclei at a wide range of angles. Studying the details of this process is key to obtaining an improved understanding of the rare cases where fusion occurs, leading to superheavy elements. For the studies to be most efficient and to ensure registration of as many reaction outcomes as possible, the unique large-area CUBE detection system at ANU, operated by the nuclear reaction dynamics group, was used, which offers superior acceptance for such events. The system registers the angle at which the events are recorded, the ratio of the masses of the two fragments, and their total kinetic energy. This allows reconstructing the reaction outcome at the moment when the fragments separate. Current theoretical descriptions of the cold fusion reactions assume that the two fusing nuclei follow a thermal diffusion-like process to evolve into a compound nucleus, which is the basis for superheavy element production. If true, the fusion suppression would be highest at the lowest excitation energies, as then, the least amount of energy is available for this diffusion process. In contrast, the measured data suggest the suppression in this step to become smaller with decreasing energy, indicating that cold fusion is not driven by a thermal diffusion process. The results call for microscopic approaches to describe this reaction step, hence stimulating further theoretical work. The evolution of the fusion mechanism when going from 48Ca towards heavier projectiles is also relevant for the production of new elements beyond element 118 (oganesson): whereas this element could be produced using a 48Ca beam, this will no longer be possible for heavier elements, due to a lack of target materials with a sufficient number of protons to reach elements 119, 120 or beyond.

The work was published in Physics Review Letters and is the latest example of the successful collaboration between the SHE chemistry department at GSI and HIM and the Institute of Nuclear Chemistry at JGU with the Nuclear Reaction Dynamics Group at the ANU, which started in 2013 and has led to numerous joint publications.

Publication: K. Banerjee et al., Mechanisms Suppressing Superheavy Element Yields in Cold Fusion Reactions, Phys. Rev. Lett. 122 (2019) 232503.

the periodic table of the elements

Figure showing the periodic table of the elements, including elements 107-112, which were discovered at GSI Darmstadt. The lower panel shows measured probabilities (given as cross sections on the left-hand y-axis and as production rates under typical experimental conditions on the right-hand y-axis) for producing elements 102 to 113 in cold fusion reactions. Black symbols show even-Z elements, produced using Pb-targets, as were used in the present experiment. The production rate is steeply decreasing with increasing atomic number. The nuclear reactions leading to elements 102, 104, and 106 (indicated in blue) have been studied in the present work at ANU Canberra, Australia. The nuclear collision outcomes that do not result in the production of a heavy element have been studied to elucidate the underlying mechanisms governing the steeply decreasing trend of superheavy element production in cold fusion reactions.

non-fusion events measured with the CUBE detector  

Figure showing non-fusion events measured with the CUBE detector for the three reactions leading to elements 102, 104, and 106. Each entry in one of the top panels represents one nuclear reaction leading to two light fragments, for which the mass ratio (x-axis) and the emission angle (y-axis) is plotted. In addition, the kinetic energy is determined (not represented in these plots). The bottom panels show the projection of all events at emission angles between 90° and 170° onto the x-axis. Fusion events lead to the central peak at mass ratios of 0.5, the abundance of which decreases with increasing projectile atomic number.

March 04, 2019

118 and Counting … The Periodic Table on its 150th Anniversary

“Is there still room for more elements in the modern periodic table with its currently 118 elements? Will we need another extra series in the periodic table besides the classical s–, p–, and d–block, and the lanthanides/actinides? Will the periodic table in this region still feature periodicity? …

Read more in Angewandte Chemie International Edition in the Guest Editorial by Christoph E. Düllmann

December 07, 2018

First Ionization Potentials of Fm, Md, No, and Lr:
Verification of Filling-Up of 5f Electrons and Confirmation of the Actinide Series

In a current paper in the Journal of the American Chemical Society (JACS), we report the first ionization potentials (IP1) of the heavy actinides, fermium (Fm, atomic number Z = 100), mendelevium (Md, Z = 101), nobelium (No, Z = 102), and lawrencium (Lr, Z = 103).

Periodic Table

Current Periodic Table. The position of the studied elements at the end of the actinide series is highlighted.
© B. Schausten, GSI

The surface ion source: grey tantalum tube in the image center, surrounded by two heating filaments. It is installed at JAEA Tokai, Japan

The first ionization potential (IP1) is the energy required to remove the most weakly bound electron from a neutral atom and is a fundamental property of any chemical element. The IP1 values were determined in an atom-at-a-time regime using a method based on a surface ionization process in a tantalum ionizer, coupled to an online mass separation technique. The efficiency of the surface ionization process depend directly on the IP1. The measured IP1 values agree well with those predicted by state-of-the-art relativistic calculations performed alongside the present measurements. The value measured for No also agrees well with the laser spectroscopic work carried out at GSI in the group of Prof. Michael Block.
Similar to the well-established behavior for the lanthanides, the (IP1)values of the heavy actinides up to No increase with filling up the 5f orbital, while that of Lr is the lowest among the actinides. These results clearly demonstrate that the 5f orbital is fully filled at No with the [Rn]5f147s2 configuration and that Lr has a weakly bound electron outside the No core. In analogy to the lanthanide series, the present results unequivocally verify that the actinide series ends with Lr.
The experiment led by our collaborators at JAEA Tokai, Japan, where it was carried out at the JAEA Tandem accelerator, in collaboration with international partners including experimenters from our group.

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April 19, 2018

A step closer to the nuclear clock

Oscillations in the atomic nucleus of thorium-229 to be used as pulse generator for future nuclear clocks

Precise time measurements play a vital role in our daily life. They allow reliable navigation and accurate experimenting and provide a basis for world-wide synchronized exchange of data. A team of researchers of PTB Braunschweig, Ludwig-Maximilians-Universität München (LMU), Johannes Gutenberg University Mainz (JGU), the Helmholtz Institute Mainz (HIM), and GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt now reports on a decisive step toward the potential development of a nuclear clock, which bears the potential to significantly outperform the best current atomic clocks. The only known excited state of an atomic nucleus that is located at a suitably low excitation energy to be accessible by optical techniques, as they are in use in current atomic clocks, exists in thorium-229. Fundamental properties of thorium-229 in this state have now been determined, the researchers report in the current issue of the journal Nature.

Atomic Clock I
Graphical representation of a nuclear clock based on a transition in the atomic nucleus of thorium-229 (left). In such a clock, the nucleus will be excited with laser light. In the present experiment, laser excitation of the electron shell allowed measurements of relevant properties of the excited, isomeric nucleus. The corresponding cut-out from the chart of nuclei, which tabulates all known atomic nuclei, is visible in the background. The thorium-229 ground state is listed with its half-life of 7932 years. The half-life of the isomeric state is only 7 μs in the neutral atom, but >60 s for the ion, as this cannot emit a loosely-bound electron. The determined nuclear properties μ and Q indicative of the charge distribution and shape are indicated as well.
Credit: Christoph Düllmann, JGU Mainz
    Atomic Clock II
The uranium-233 source (large disk in center of image) produced at the Johannes Gutenberg University Mainz, Germany, mounted inside the experimental apparatus at the Ludwigs-Maximilian-University Munich, Germany. Components of the setup are reflected in the surface of the source.
Credit: Lars von der Wense, LMU Munich

Some 15 years ago, researchers at PTB in Braunschweig, the National Metrology Institute of Germany, developed a concept for the design of a novel optical clock with unique characteristics. Instead of exploiting oscillations in the electron shell, they proposed that one could make use of a transition between energy levels within an atomic nucleus as the basis for a nuclear clock. Because the protons and neutrons in the nucleus are orders of magnitude more densely packed and much more tightly bound than the electrons in the outer electron shells, they are much less susceptible to perturbation by outside forces that might affect their transition frequencies. Therefore, a nuclear clock should be far more stable and precise than present-day optical atomic clocks. However, the typical frequencies of nuclear transitions are much higher than those that occur in electron shells and generally lie in the gamma-ray region of the electromagnetic spectrum. This means that they cannot serve as the basis for an optical atomic clock, as all such clocks are based on excitation by microwaves or laser light.

The exception to this rule is found in an unstable isotope of thorium, thorium-229, which exhibits a quasi-stable, so-called isomeric nuclear state with an extraordinarily low excitation energy. The frequency of the transition between the ground state and this isomeric state corresponds to that of ultraviolet light. This transition can therefore be induced by means of a laser-based technique similar to that used in state-of-the-art optical atomic clocks. More than ten research groups worldwide are now working on the realization of a nuclear clock based on the thorium-229 isomer. Experimentally speaking, this is an exceedingly challenging endeavor. While the existence of the state was inferred from data obtained over several decades, the direct detection and hence unambiguous proof of its existence in the first place was achieved in 2016 in collaborative work of the LMU group together with the groups in Mainz and Darmstadt. They subsequently succeeded in measuring its half-life. However, it has not been possible to observe the nuclear transition by optical means yet, as the exact excitation energy of the isomer has not been determined with sufficient precision. The transition itself is extremely sharp – as required for timing purposes – and can only be induced if the frequency of the laser light corresponds exactly to the difference in energy between the two states. The quest for the magic frequency may be compared to the proverbial search for a needle in a haystack.

Measuring the basic features of the thorium-229 isomer

A collaborative effort by researchers and engineers at PTB, LMU, Johannes Gutenberg University Mainz, the Helmholtz Institute Mainz, and GSI Helmholtzzentrum für Schwerionenforschung has now achieved an important breakthrough in this search. The researchers have now measured some of the basic features of the thorium-229 isomer, such as the size of its nucleus and the general form of the distribution of protons. In the present study, the nuclei were not excited from the ground state by means of laser light, as they would be in a future clock. Instead, the isomer was produced by the alpha-decay of uranium-233 and decelerated in a device developed at LMU, extracted, and stored in an ion trap as Th2+ions. The uranium-233 source was provided by the groups in Mainz und Darmstadt. For this purpose, uranium-233 was chemically purified and its decay products were removed to avoid any influence on the measurements. Subsequently, suitable sources were deposited as homogenous thin films on a silicon layer in an electrochemical procedure for the laser experiments of PTB at the LMU apparatus. Christoph Düllmann, professor at the Institute of Nuclear Chemistry at Johannes Gutenberg University Mainz and head of the involved research teams at HIM and GSI, said: «This is a fascinating interdisciplinary team of physicists and chemists studying a topic that connects nuclear and atomic physics. Our contribution is testimony to the need of nuclear chemistry expertise in the preparation of samples suitable for experiments in a variety of fields in contemporary physics and chemistry research.»

With the aid of laser systems specifically developed for spectroscopic analyses of this ionic species at PTB, researchers have now been able to determine the transition frequencies in the electron shell of Th2+. These parameters are directly influenced by the state of the nucleus and encode valuable information on its physical properties. On the basis of theoretical modeling alone, it has not been possible to predict how the structure of the thorium-229 nucleus in this unusually low-excited isomer might behave.

Professor Thomas Stöhlker, Vice Director of Research and head of the Atomic Physics division at GSI, added: «These fantastic new results are very helpful to determine the energy of the transition of Th-229 in future experiments at the storage rings of GSI and FAIR with high precision.» Furthermore, it is now possible to probe the structure of the electron shell to confirm a successful laser-excitation of the nucleus into the isomer. The hunt for determining the optical resonance frequency that triggers the transition to the isomeric first excited state of the thorium-229 nucleus is not yet over. But researchers now have a far better idea of what the needle in the haystack really looks like.

Johannes Thielking, PTB scientist, with the laser setup used for investigating the thorium-229 nucleus.
Credit: PTB Braunschweig



The isotope 229Th is the only nucleus known to possess an excited state 229mTh in the energy range of a few electronvolts—a transition energy typical for electrons in the valence shell of atoms, but about four orders of magnitude lower than typical nuclear excitation energies. Of the many applications that have been proposed for this nuclear system, which is accessible by optical methods, the most promising is a highly precise nuclear clock that outperforms existing atomic timekeepers. Here we present the laser spectroscopic investigation of the hyperfine structure of the doubly charged 229mTh ion and the determination of the fundamental nuclear properties of the isomer, namely, its magnetic dipole and electric quadrupole moments, as well as its nuclear charge radius. Following the recent direct detection of this long-sought isomer, we provide detailed insight into its nuclear structure and present a method for its non-destructive optical detection.

Johannes Thielking1, Maxim V. Okhapkin1, Przemysław Głowacki1, David M. Meier1, Lars von der Wense2, Benedict Seiferle2, Christoph E. Düllmann3,4,5, Peter G. Thirolf2 & Ekkehard Peik1
Laser spectroscopic characterization of the nuclear clock isomer 229mTh
Nature, 556, 321-325 (2018)
DOI: 10.1038/s41586-018-0011-8

*Corresponding author

Involved Institutes

  1. Physikalisch-Technische Bundesanstalt (PTB), Braunschweig
  2. Ludwig-Maximilians-Universität München (LMU), Garching
  3. GSI Helmholzzentrum für Schwerionenforschung GmbH, Darmstadt
  4. Helmholtz Institut Mainz (HIM), Mainz
  5. Johannes Gutenberg Universität Mainz, Mainz

News Announcements

  • Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (german, english, April 17, 2018)
  • Ludwig-Maximilians-Universität München (LMU) (english, April 19, 2018)
  • Johannes Gutenberg University Mainz, Germany (german, english, April 19, 2018)
  • GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany (german, english, April 18, 2018)

February 26, 2018

The Quest for Superheavy Elements and the Island of Stability

A race is on to create the world's heaviest elements — and to explore the periodic table's “island of stability,” where these elements exist for more than a moment
Article in "Scientific American", issue March 2018 by Christoph E. Düllmann and Michael Block.

December 14, 2017
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September 21, 2017

Michael Götz wins first poster prize at annual meeting of the nuclear chemistry section of the GDCh in September 2017 in Berlin

The poster prize winners (l. to r.) Roger Kloditz (HZDR Dresden-Rossendorf), Michael Götz (JGU Mainz/HIM Mainz/GSI Darmstadt), and Hauke Bosco (LU Hanover) with the Nuclear Chemistry section chair, Ch. Düllmann.

Michael Götz, PhD student in our group, is the winner of the first poster prize at the annual meeting of the Section Nuclear Chemistry of the German Chemical Society (GDCh) at the Wissenschaftsforum Chemie 2017 in Berlin. The topic of his poster is "The in-situ synthesis of carbonyl complexes of short-lived transition metal isotopes without physical preseparation". Congratulations!

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December 12, 2016

Direct detection of elusive thorium-229 isomer among "Physics World Top Ten Breakthroughs of the Year 2016"

The direct detection of the exotic isomeric state in thorium-229 at the LMU Munich, achieved in collaboration with our group, belongs to the IOP's "Physics World Top Ten Breakthroughs of the Year 2016" as identified according to their fundamental importance of research, significant advance in knowledge, strong connection between theory and experiment, and general interest to all physicists. The work lays a basis for next steps on the way to a potential future "nuclear clock" built upon the ground state transition of this isomeric state. Such a clock's precision might significantly surpass that of the best current timekeepers, the atomic clocks.

The work, led by PD Dr. Peter Thirolf and Dr. Lars von der Wense from LMU, is published in the May 05 issue of Nature (see also accompanying "News & Views" feature by M. Safronova). Further information is available from the LMU Munich group, the NuClock consortium, and media releases from GSI and the Johannes Gutenberg University Mainz that appeared when the paper was published.

More Info see below...

September 29, 2016

Nobelium in the limelight – Atom-at-a-time laser spectroscopy at SHIP gives first insight in heavy element's atomic structure

The analysis of atomic spectra is of fundamental importance for our understanding of atomic structures. Until now, researchers were unable to examine heavy elements with corresponding optical spectroscopy because these elements do not occur in nature and cannot be artificially created in weighable amounts. However, an international team of scientists and engineers led by Dr. Mustapha Laatiaoui (SHE physics department at GSI and HIM) and Prof. Michael Block (GSI, HIM and JGU Mainz) together with collaborators from our own department as well as several other research groups have now looked for the first time into the inner structure of heavy elements.

As reported in a paper in Nature, the ground state transition in nobelium (element 102) from the 1S0 ground state to the 1P1 excited state was characterized with high precision, as is typical for laser-based studies. Furthermore, from the observation of high-lying Rydberg states, information on the IP1 was obtained. Studies included the isotopes 252No and 254No, yielding information on the isotope shift, giving access to nuclear properties. The obtained data are in good agreement with current Relativistic Coupled Cluster and Multi Configuration Dirac Fock-based theoretical calculations. A schematic of the experimental setup is shown in the Figure below.

Schematic of the experimental setup for the laser spectroscopic studies of No. No ions (denoted by ) are separated from the primary 48Ca beam by the velocity filter SHIP, which they exit through a 3.5 μm Mylar foil acting as a vacuum window. They are stopped in a buffer gas cell filled with 95 mbar Ar, and collected on a Ta filament. Periodically, the filament is heated to 1350 K, which leads to evaporation of No in elemental form (). Two tunable laser beams shining into the volume provide for two-step resonance ionization. Formed No ions are guided by extraction electrodes onto a PIPS α detector, where the radioactive decay of the No isotope under study is registered.
Figure: Mustapha Laatiaoui / GSI/HIM

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June 29, 2016

The chemistry is right not only in element 113: Helmholtz International Fellow Professor David Hinde from Australia is guest of GSI and HIM

Professor David Hinde, Director of the Heavy Ion Accelerator Facility at the Australian National University (ANU) in Canberra (Australia), recently received the Helmholtz International Fellow Award. The prize, of EUR 20.000, also enables the award winner to undertake research at a Helmholtz center. Hinde, a leading expert in the field of nucleus-nucleus collisions, is using this award to strengthen cooperation with the GSI Helmholtzzentrum für Schwerionenforschung (GSI) and the Helmholtz Institute Mainz (HIM). Quite recently he made another research visit to Darmstadt and Mainz.

A central subject there was the chemistry of the recently officially recognized element 113 which, according to IUPAC, was discovered in Japan and has recently been proposed to be given the name "Nihonium". Professor Hinde, as a member of a collaboration project managed by the Superheavy Elements Chemistry (SHE Chemistry) Department, was a guest for one week at the TASCA recoil separator. There, 40 scientists and engineers from ten research centers are collaborating. The objective of the three-week experiment was to study the chemical characteristics of the element. Another main subject of the visit was planning of the next joint experiments of the two research groups, to be carried out at the ANU accelerator in Australia. A very close partner is also the Institute for Nuclear Chemistry of Johannes Gutenberg University Mainz, which also cooperates within HIM. After the visit to the Rhine-Main region, he attended a symposium in Sweden on superheavy elements, then returned to his homeland of Australia.

This visit strengthens the intensive scientific exchanges between the Australian researchers and their colleagues at GSI and HIM. Research collaboration started five years ago, and was intensified from 2012 by Professor Hinde and Christoph Düllmann, professor at the Johannes Gutenberg University Mainz and Head of the SHE Chemistry Departments at GSI and HIM. Hinde remembers: "Christoph came in 2012 to a conference in Australia; we met there and soon decided to strengthen our collaboration." As a result of the joint research interests and the complementary research infrastructure at ANU and GSI, an increasingly strong cooperation was developed in recent years between the research groups in Germany and Australia. Research experiments have been conducted at ANU since 2011 and at GSI since 2012. "GSI has excellent tools, which are among the best in the world", says Hinde.

The nomination of David Hinde for the Helmholtz International Fellow Award has also arisen from this cooperation and was initiated by HIM via GSI. Christoph Düllmann, who himself was in Canberra for several months in the past winter and worked together with Hinde and other members of his research group on joint experiments on the tandem-accelerator, points out: "David Hinde is a recognized expert in fundamental high-precision research on low-energy nuclear fusion reactions covering a large area of the chart of the nuclides. Under his direction, unique devices were built for such research, which optimally use the precision beam characteristics of the ANU accelerator."

This is a complex subject, but it is based on a very simple stimulus which led the now 59-year-old English-born researcher to his career choice: "I love physics, and it should not sound like bragging, but I am good at what I do. I have always wanted to know how things in nature function." The married father of two grown-up children has known Germany for many years, since in the late 1980s he worked for two years at the Hahn-Meitner Institute in Berlin, which is today the Helmholtz Center Berlin (HZB). And how did he get to know the GSI? Get to know does not appear to be the right word because Hinde says simply: "Everybody knows the GSI. It is famous around the world."

Hinde still remembers with pleasure one key moment: During a conference in 1996, Professor Peter Armbruster reported about the discovery at GSI of element 112 (Copernicium) – and described the long alpha-particle decay chain from 112 as “a poem of physics”. Hinde has never forgotten those words: "I found this very inspiring, this passion and poetry. For me this was a strong motivator for my subsequent work."

D. Hinde

During his research stay, the Australian Professor David Hinde worked on the TASCA recoil separator at GSI; on the photo, he adjusts the correct time range for the beam pulse.
Photo: Gabi Otto / GSI

May 2016
TASCA16 workshop 

May 09, 2016

One step closer to the development of an ultra-precise nuclear clock

Measuring time using oscillations of atomic nuclei might significantly improve precision beyond that of current atomic clocks. Physicists have now taken an important step toward this goal.

Atomic clocks are currently our most precise timekeepers. The present record is held by a clock that is accurate to within a single second in 20 billion years. Researchers led by physicist PD Dr. Peter Thirolf and his team at LMU Munich and including scientists and engineers from Johannes Gutenberg University Mainz, the Helmholtz Institute Mainz, and the GSI Helmholtz Centre for Heavy-Ion Research in Darmstadt have now experimentally identified a long-sought excitation state, a nuclear isomer in an isotope of the element thorium (Th), which could enhance this level of accuracy by a factor of about ten. Their findings are reported in the scientific journal Nature.

      Atomic Clock I
Graphical representation of a nuclear clock based on a transition in the atomic nucleus of thorium-229 (left). For the first time, electrons emitted in the deexcitation of the isomer into the ground state (top right) could be directly detected. The corresponding cut-out from the chart of nuclei, which tabulates all known atomic nuclei, is visible in the background. The thorium-229 ground state is listed with ist half-life of 7932 years, while the now directly detected isomer with >60 s half-life.
Credit: Christoph Düllmann, JGU Mainz
    Atomic Clock II
The uranium-233 source (large disk in center of image) produced at the Johannes Gutenberg University Mainz, Germany, mounted inside the experimental apparatus at the Ludwigs-Maximilian-University Munich, Germany. The thorium-229m atoms emerge from the perfectly smooth surface to the left into the separation stage and unltimately into the detector (not visible). Components of the setup responsible for creating the ultraclean conditions that were necessary for these studies are reflected in the surface of the source.
Credit: Lars von der Wense, LMU Munich
Oscillations as the heart of timekeeping

The second is our basic unit for the measurement of time. In today’s conventional atomic clocks, the time of a second is tied to the oscillation period of electrons in the atomic shell of the element cesium (Cs). The best atomic clock currently in use boasts a relative precision of almost 10-18. "Even greater levels of accuracy could be achieved with the help of a so-called nuclear clock, based on oscillations in the atomic nucleus itself rather than oscillations in the electron shells surrounding the nucleus," said Thirolf. "Furthermore, as atomic nuclei are 100,000 times smaller than whole atoms, such a clock would be much less susceptible to perturbation by external influences."

However, of the more than 3,300 known types of atomic nuclei only one potentially offers a suitable basis for a nuclear clock, and that is the nucleus of the thorium isotope with atomic mass 229 (Thorium-229), which, however, does not occur naturally. For over 40 years physicists have suspected this nucleus to exhibit an excited state with energy only very slightly above that of its ground state. The resulting nuclear isomer, Th-229m, possesses the lowest excitation state in any known atomic nucleus. Furthermore, Th-229m is expected to show a rather long half-life from between minutes to several hours. It should thus be possible to measure with extremely high precision the frequency of the radiation emitted when the excited nuclear state falls back to the ground state.

First direct detection of the transition

Direct detection of the thorium isomer Th-229m has never before been achieved. "Up until now, the evidence for its existence has been purely indirect," said Thirolf. In a complex experiment, the researchers involved have now succeeded in detecting the elusive nuclear transition. They made use of uranium-233 as a source of Th-229m, which is produced in the radioactive alpha decay of uranium-233. "The uranium-233 was chemically purified by our team including Mainz- and Darmstadt-based experts and was deposited as an ultrapure thin layer on a titanium-covered silicon wafer as used in the semiconductor industry. This uranium-233 source was then transferred to Munich, where it was mounted in the experimental apparatus, providing the desired Th-229m", explained Professor Christoph Düllmann, the head of the groups in Mainz and Darmstadt.

In an experimental tour-de-force, the scientists isolated the isomer as an ion beam. "Using a microchannel plate detector, we were then able to measure the decay of the excited isomer back to the ground state of Th-229 as a clear and unambiguous signal. This constitutes direct proof that the excited state really exists," said Thirolf. "This breakthrough is a decisive step toward the realization of a working nuclear clock," emphasized the LMU physicist. "Our efforts to reach this goal in the framework of the European Research Network nuClock will now be redoubled. The next step is to characterize the properties of the nuclear transition more precisely, i.e., its half-life and, in particular, the energy difference between the two states. These data will allow laser physicists to set to work on a laser that can be tuned to the transition frequency, which is an important prerequisite for an optical control of the transition." Professor Thomas Stöhlker, research director at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, added: “These new findings are very valuable for our experiments with TH-229m planned at the GSI/FAIR storage ring, particularly those concerning the determination of the energy of the nuclear transition."



Today’s most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of an atomic shell transition. There is only one known nuclear state that could serve as a nuclear clock using currently available technology, namely, the isomeric first excited state of 229Th (denoted 229mTh). Here we report the direct detection of this nuclear state, which is further confirmation of the existence of the isomer and lays the foundation for precise studies of its decay parameters. On the basis of this direct detection, the isomeric energy is constrained to between 6.3 and 18.3 electronvolts, and the half-life is found to be longer than 60 seconds for 229mTh2+. More precise determinations appear to be within reach, and would pave the way to the development of a nuclear frequency standard.

Lars von der Wense*1, Benedict Seiferle1, Mustapha Laatiaoui2,3, Jürgen B. Neumayr1, Hans-Jörg Maier1, Hans-Friedrich Wirth1, Christoph Mokry3,4, Jörg Runke2,4, Klaus Eberhardt3,4, Christoph E. Düllmann2,3,4, Norbert G. Trautmann4 & Peter G. Thirolf1
Direct detection of the 229Th nuclear clock transition
Nature, 533, 47-51 (2016)
DOI: 10.1038/nature17669

*Corresponding author

Involved Institutes

  1. Ludwig-Maximilians-Universität München, Garching, Germany
  2. GSI Helmholzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
  3. Helmholtz Institute Mainz (HIM), Mainz, Germany
  4. Johannes Gutenberg University Mainz, Mainz, Germany

News Announcements

  • Johannes Gutenberg University Mainz, Germany (german, english, May 06, 2016)
  • GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany (german, english, May 04, 2016)

December 11, 2015

Last known magic neutron number weakens in heavy elements

An international team of scientists has succeeded to create and detect extremely short-lived atomic nuclei of the element uranium. Having far fewer neutrons than the kind of uranium nuclei found in nature, they exist only for about a millionth of a second. The new data provide key information on how the numbers of neutrons and protons inside exotic heavy nuclei influence their stability. This is important to give better guidance for experiments on the search for new superheavy elements.

In atomic nuclei, protons and neutrons arrange in individual shells. Nuclei containing just the right numbers to fill a proton and a neutron shell are considerably more stable than their neighbours. For protons, 82 is the last known of these “magic numbers”, while it is 126 for neutrons. This makes lead-208, with 82 protons and 126 neutrons, the heaviest “doubly-magic nucleus” known to date. Lead-208 is the main ingredient in lead as used in daily life like in car batteries. For decades, scientists tried finding out how many protons will fit into the next shell, which was conjectured to give rise to an "island of stability" in the region of superheavy elements. Current theoretical models still disagree: some favor 114, others prefer 120 or even 126. Element 114 is known, but can be studied at rates of only about one atom per day. Elements 120 and 126 are yet unknown. Scientists thus look for other experimental data allowing to refine their models.

In their recent work, an international team led by Dr. Jadambaa Khuyagbaatar from the Helmholtz Institute Mainz, Germany, and the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany, traced this last neutron shell closure towards heavier elements. The question is whether the neutron number 126 remains as dominant in these increasingly unstable nuclei as it is known to be in lead-208. For this, they produced nuclei uranium, with extra ten protons when compared to lead. Usual uranium nuclei as found in nature, like uranium-238, have far more neutrons than around 126, so the researchers first produced the new uranium-221 and acquired new and improved data on uranium-222, of which only three atoms were observed in a study dating back to 1983.

For this, an intense beam of titanium-50 ions (element 22) was accelerated at GSI Darmstadt and used to irradiate a foil containing ytterbium-176 (element 70). Fusion led to uranium nuclei (element 92), which were separated in the gas-filled recoil separator TASCA and guided to a detector suitable to register their decay. In this way, the team studied these nuclei's instability and found them to decay within microseconds. Such short lifetimes could only be registered thanks to a new, advanced data acquisition system and data analysis techniques. The study of combined data of isotopes of elements from lead up to uranium at and above the 126 neutron shell suggests this to no longer be a pronounced magic neutron number in uranium. These data allow benchmarking models that, e.g., guide efforts to search for new superheavy elements.

The work was published on December 10, 2015 in the scientific journal The Physical Review Letters (J. Khuyagbaatar et al., Phys. Rev. Lett. 115 (2015) 242502) and is highlighted here.


The figure shows one of eighty-one registered traces of a triple-signal associated with the implantation of uranium-222 into the detector (red), its emission of an α particle with 9.31 MeV energy (blue) leading to thorium-218, followed by the very fast α decay of this latter nucleus by emission of a 9.67 MeV α particle (green), leading to 214Rn, the decay of which occurred after the end of the shown trace but was registered in a different branch of the data acquisition system.
Picture: J. Khuyagbaatar / HIM&GSI

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December 2015

Special Issue on Superheavy Elements

Credit: Elsevier B.V.
The December 2015 issue of Nuclear Pyhsics A is a " special issue on superheavy elements" and contains an up-to-date compilation of overview articles written by experts in the field, embracing all aspects of these exotic elements.

Covered topics include:
  • Synthesis
  • Nuclear Structure
  • Atomic Physics
  • Chemistry
Members from our group are among the authors as well as the editors for this volume.
Enjoy reading!

November 2015

Helmholtz International Fellow Award for Professor David Hinde, ANU Canberra

Prof. Maas, Prof. Hinde

Helmholtz International Fellow Award winner Professor David Hinde of the Australian National University, Canberra, Australia (right) and Professor Frank Maas, director of the Helmholtz Institute Mainz − HIM − (left) on the rooftop of the newly constructed HIM Building on the campus of the Johannes Gutenberg University Mainz celebrating the award on the occasion of the visit of the winner to Mainz in September 2015. (Photo: Ch. Düllmann, U. Mainz)

Professor Dr. David Hinde is Director of the Heavy Ion Accelerator Facility at the Australian National University (ANU) Canberra, Australia. He is a world renowned expert in fundamental high-precision studies of low energy nuclear fusion reactions across a wide mass range of the chart of nuclei. Unique instruments for such studies, called "CUBE" and “SOLITAIRE”, have been constructed and exploited under his leadership. These perfectly exploit the precision beam characteristics, including the excellent micro-timestructure, of the ANU Heavy Ion Accelerator Facility, based at the Department of Nuclear Physics. Thanks to the superb performance of the CUBE, the dynamics of the fusion process of two atomic nuclei can be recorded on a timescale of 10-21 s, thus bringing new understanding to phenomena facilitating or hindering the fusion of two colliding nuclei.

Read more in english and german ...

September 2015

Giersch-Excellence-Award 2015 for Paul Scharrer

Paul Scharrer, PhD student in the SHE Chemistry Research Section of the Helmholtz Institute Mainz (HIM) has been awarded "Giersch Excellence Award" for outstanding scientific work in the past years and is invited to join the Graduiertenschule Giersch.

The topic of his thesis project is the fundamental investigation of electron stripping processes of slow heavy ions in gaseous media. Besides being of key importance for the study of superheavy elements in gas-filled recoil separators like TASCA at GSI, which was successfully used for the identification of elements 114, 115, and 117 as well as for sensitive searches for the new elements 119 and 120, such processes are exploited to produce highly charged ions suitable for heavy ion beam acceleration at GSI and at the future FAIR accelerator facility. The focus of Paul Scharrer's work is on the electron stripping of heavy projectiles used as heavy ion beams at GSI and at heavy ion accelerator centers around the world. Typically, projectiles like 238U are initially produced in a comparatively low charge state (4+ at GSI), which is not well suited for acceleration to high energies. Therefore, after having reached 1.4 MeV/u in the first accelerator stage, the projectiles pass through a gas-filled region, where they are stripped of electrons, which increases their charge state.
Together with his colleagues from the SHE Chemistry Department at GSI and HIM and the Linac and Operations (L&O) Department within the FAIR@GSI division, Paul Scharrer developed a new gas stripper setup, which exploits the low duty cycle of the FAIR facility. The new setup employs pulsed gas injection, delivering gas only while beam is passing. This allowed reducing the gas load dramatically, allowing for significantly higher gas densities during beam passage to be achieved, despite the limited pumping capacity and the strict vacuum requirements in the adjacent accelerator sections. Furthermore, the new setup allows use of any gas, unlike the previously used stripper, which was exclusively based on N2. Guided by theoretical studies from Prof. V. Shevelko from the Lebedev Physical Institute in Moscow, Russia, who was a HIM Visiting Fellow for several months in 2013-2015 to support the work, systematic studies showed a pulsed hydrogen-based stripper to be superior. The efficient stripping process in hydrogen gas allowed achieving a new record 238U28+ intensity at the UNILAC, exceeding the previous highest values by more than 50%, and already reaching more than 65% of the FAIR design beam brilliance. Besides the perspective to achieve yet higher average charge states for most of the ion species at higher H2-density, the new setup offers opportunities for operation as a pulsed stripper, where every pulse can be tailored to different projectiles from the two ion source terminals feeding this accelerator line. "This significantly enhances the versatility of the UNILAC accelerator and is also a critical step towards the FAIR facility" explains Dr. Winfried Barth from GSI's L&O department. Christoph Düllmann, professor at Johannes Gutenberg University Mainz and head of the SHE Chemistry department at GSI and HIM adds "Paul's work highlights the close connection of basic research like studies on production and properties of superheavy elements, and technical advances that arise, sometimes in fields that appear rather remote at first glance".

Paul Scharrer in front of the gas-stripper section of the UNILAC accelerator at GSI.
Photo: Ch. Düllmann / GSI



July 01, 2015

TASCA14 workshop

August 07, 2015

Samples prepared at Johannes Gutenberg University Mainz facilitate direct measurement of the mass difference of
163Ho and 163Dy to solve the Q-Value puzzle for
the neutrino mass determination

Using samples of 163Ho that were prepared at the Institute for Nuclear Chemistry at the Johannes Gutenberg University Mainz, the atomic mass difference of 163Ho and 163Dy has been directly measured with the Penning-trap mass spectrometer SHIPTRAP at GSI Darmstadt by applying the novel phase-imaging ion-cyclotron-resonance technique. Our measurement has solved the long-standing problem of large discrepancies in the Q value of the electron capture in 163Ho determined by different techniques. Our measured mass difference shifts the current Q value of 2555(16) eV evaluated in the Atomic Mass Evaluation 2012 by more than 7σ to 2833 (30stat) (15sys) eV/c2. With the new mass difference it will be possible, e.g., to reach in the first phase of the ECHo experiment a statistical sensitivity to the neutrino mass below 10 eV, which will reduce its present upper limit by more than an order of magnitude. The results were published in Physical Review Letters on August 05, 2015 (S. Eliseev et al., Physical Review Letters 115, 062501 (2015)).

163Ho was produced by intense neutron irradiation of 162Er at the high-flux reactor at the Institute Laue Langevin at Grenoble, France and subsequently purified by using radiochemical separation techniques similar to those also used in research on the heaviest elements.

More information:

Holger Dorrer with Ho-163
Holger Dorrer from Johannes Gutenberg University Mainz on the platform of the research reactor TRIGA Mainz that was used to verify the purity of the sample. He holds the produced and separated 163Ho.
Credit: H.-M. Schmidt / JGU Mainz
Comparison of values reported for the Q-value of the 163Ho electron capture decay over time.
Credit: ECHo collaboration

April 09, 2015

Cover story of this week's issue of Nature:

Measurement of the First Ionization Potential of Lawrencium,
Element 103

Credit: NATURE Magazine

Ionization potential of heavy lanthanides (black symbol) and actinides (red symbol) including our present results for Lr. A closed and open symbol indicates an experimental and estimated value, respectively.
Credit: T.K. Sato / JAEA

The most dramatic modern revision of the Mendeleev’s periodic table of elements came in 1944, when Glenn T. Seaborg placed a new series of elements, the actinides (atomic numbers 89–103), below the lanthanides. In this issue our report on the first measurement of one of the basic atomic properties of element 103 (lawrencium), its first ionization potential, is included. Lawrencium is accessible only as short-lived isotopes via atom-at-a-time synthesis in heavy-ion accelerators, so experimental investigations of its properties rare. The experimental results, agreeing with state-of-the-art theoretical calculations, show that the last valence electron in lawrencium is the most weakly-bound one in all actinides and any other element beyond group 1 of the periodic table. This signature confirms the end of the actinide series at element 103 and validates the architecture of the periodic table in this region, where relativistic effects play a crucial role.

Nature 520, 209-211 (2015)
"News & Views" by Prof. Andreas Türler:
Nuclear chemistry: Lawrencium bridges a knowledge gap
Nature 520, 166-167 (2015)
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January 2015

Observation of Element 117 at GSI Among Top Ten Physics News Stories in 2014

The synthesis of element 117 at GSI belongs to the Top Ten Physics News Stories in 2014 published by American Physical Society (APS).

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Every year, APS News identifies the top ten physics news stories that were most widely recognized by the public. The 2014 list features highlights like indications for gravitational waves from the BICEP2 telescope, intergalactic neutrinos from IceCube, the Rosetta/Philae mission to the comet 67P/Churyumov-Gerasimenko, or the blue LEDs that won their developers the physics nobel prize. We are most delighted to find our element 117 experiment at TASCA published by J. Khuyagbaatar et al. in Phys. Rev. Lett. 112 (2014) 172501 included in this venerable list.

Phys. Rev. Lett. 112, 172501 (2014)
Synopsis: Element Z=117 Confirmed

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November 10, 2014

Intensity record for uranium 28+ at UNILAC

"GSI Kurier" 46 - 2014; November, 10 - November, 16, 2014 (no longer available)

27. Oktober 2014

TASCA14 workshop

TASCA workshop 2014
Photo: G. Otto / GSI

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September 19, 2014

Seaborgium Hexacarbonyl Sg(CO)6: First Carbonyl Complex of a Superheavy Element

GARIS gas-filled recoil separator seaborgium hexacarbonyl molecule - COMPACT
Dr. Julia Even from the Helmholtz Institute in Mainz, Germany and Dr. Hiromitsu Haba from RIKEN, Wako, Japan prepare the GARIS gas-filled recoil separator (top right) for connection to the Recoil Transfer Chamber chemistry interface (bottom center). Credit: M. Schädel Graphic representation of a seaborgium hexacarbo-
nyl molecule on the silicon dioxide covered detectors of a COMPACT detector array.
Credit: A. Yakushev (GSI) / Ch.E. Düllmann (Univ. Mainz)

Science 345, 1491 (2014)

"Seaborgium Chemistry" on "The Periodic Table of Videos"

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August 21, 2014

TASCA14 workshop

May 01, 2014

Superheavy Element 117 Confirmed - On the Way to the "Island of Stability"

A part of the TASCA collaboration presents data on element 117 at GSI Darmstadt
Photo: G. Otto / GSI (HighRes Photo)

Phys. Rev. Lett. 112, 172501 (2014)
Synopsis: Element Z=117 Confirmed

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March 2014

Element 115 Experiment Reaches APS Top Ten List of "Physics Newsmakers of 2013"

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