News & Dates
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.
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
are separated from the primary 48Ca beam by the velocity filter SHIP, which they exit through a
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
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."
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
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.
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)
- Ludwig-Maximilians-Universität München, Garching, Germany
- GSI Helmholzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
- Helmholtz Institute Mainz (HIM), Mainz, Germany
- Johannes Gutenberg University Mainz, Mainz, Germany
- Johannes Gutenberg University Mainz, Germany (german, english, May 06, 2016)
- GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany (german, english, May 04, 2016)
December 11, 2015
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
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:
Helmholtz International Fellow Award for Professor David Hinde, ANU Canberra
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.
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
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
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.
- ECHo Collaboration website
- University of Mainz press release
- Press release of the Max Planck Institute for Nuclear Physics in Heidelberg on idw
- here on this website
- on the GSI website
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
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)
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).
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.
November 10, 2014
"GSI Kurier" 46 - 2014; November, 10 - November, 16, 2014
27. Oktober 2014
September 19, 2014
|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"
August 21, 2014
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)