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News Archive 2012

20.12.12: Shutdown of accelerator experiments at the MPIK
The 12 MV-tandem accelerator has a history of 45 years of successful operation

After more than 50 years the long tradition of experiments with accelerated ion beams for nuclear, atomic and accelerator physics at the Max Planck Institute of Nuclear Physics in Heidelberg has come to an end. The test storage ring TSR, lately favoured for experiments, as well as four particle accelerators for producing a variety of different ion beams were shut down at the end of the year. This measure was necessary in order to mobilise capacities for the preparation of novel experiments with the new cryogenic storage ring CSR.

The TSR was worldwide the first storage ring for high energy heavy ion beams. Phase space electron- and laser cooling systems opened up new experimental possibilities with beams of unprecedented low energy spread and emittance. The new CSR will continue in this tradition by offering an extreme space-like environment for experiments with low energy beams of charged atoms and molecules of virtually unlimited masses.

The 12 MV-tandem accelerator with its history of 45 years of successful operation (photo) as well as the high frequency post accelerator were shut down during a small ceremony on December 17, 2012 in the presence of many past and present members of staff.

It is planned to give the TSR a new lease of life at CERN external Link in Geneva where it will be used for research on radioactive ion beams supplied by HIE-ISOLDE external Link.

20.11.12: Progress in the search for neutrinoless double-electron capture

In recent years various new developments have occurred in almost all aspects related to double-beta decay, an extremely rare nuclear decay. These exciting developments triggered the idea of a focus section in "Journal of Physics G: Nuclear and Particle Physics" on double-beta decay. The special issue has now been published, please read more … >

Especially the observation of neutrinoless double-electron transformations would be of major importance for neutrino physics. It would prove the Majorana nature of neutrinos and the violation of the conservation of the total lepton number. The neutrinoless mode of double-beta decay is the most probable process, but persistent experimental attempts to observe it have been unsuccessful so far.
Within the special issue our group member S. A. Eliseev et al. report on the progress in the search for neutrinoless double-electron capture. This search can be a good alternative to the neutrinoless double-beta-decay experiments in shedding light on such aspects of neutrino physics as the neutrino type, non-conservation of the total lepton charge and magnitude of the effective Majorana neutrino mass.
The recent progress of high-precision Penning-trap mass spectrometry has allowed for measurements of the Q-values of potentially resonantly enhanced transitions with an accuracy of a few 100 eV. Mass differences for 14 pairs of nuclides connected with double-electron capture have already been measured. At present, two transitions can be of interest in the search for neutrinoless double-electron capture: 152Gd -> 152Dy and 156Dy -> 156Gd

Please read more in the article ... >

18.10.12: Pauline Ascher receives Humboldt Research Fellowship

Our division member Dr. Pauline Ascher has received a two-year Humboldt Research Fellowship external Link for postdoctoral researchers, which has been started on October 1st, 2012. Within this grant, a new Penning trap will be built at MPIK Heidelberg in the context of the PIPERADE project external Link. This project consists of the development of a new set-up to purify the beam at the future DESIR facility, the low-energy part of the future SPIRAL2 project external Link (Ganil, Caen). Some measurements will first be performed at the FT-ICR lab (MPIK), in order to find an efficient purification method for the exotic beams delivered to DESIR.
Pauline Ascher completed her PhD thesis on the "Study of the two-proton radioactivity of 54Zn with a Time Projection Chamber" in 2011 at CENBG external Link in Bordeaux. We cordially congratulate her on receiving this prestigious Humboldt Research Fellowship.

04.09.12: First Test of the Isobaric Multiplet Mass Equation in fp-Shell Nuclei

The fundamental concept of isospin symmetry allows us to classify states with quantum numbers T and Tz in addition to, e.g., spin J and parity π. States in isobaric nuclei with the same T and Jπ that have very similar structure and properties can be considered as members of an isobaric multiplet. The masses of the members of an isobaric multiplet are related by the isobaric multiplet mass equation (IMME). In case of isospin symmetry, this equation should follow a quadratic dependence on isospin projection Tz. In the recent years, precision tests of IMME became possible due to access to accurate mass data.

In a just in Physical Review Letters published article Y. H. Zhang et al. report on the new mass measurements conducted at the HIRFL-CSR accelerator complex external Link (pictures external Link) at the Institute of Modern Physics in Lanzhou, China. The masses of stored ions were measured with a precision of 20–40 keV employing the Isochronous mass spectrometry (IMS) technique. The accurately measured masses of the Tz = -3/2 nuclei 41Ti, 45Cr, 49Fe and 53Ni allowed to perform the first experimental test of IMME in the fp-shell. A breakdown of the generally accepted quadratic form of IMME for the A = 53 (T = 3/2) quartet has been found. The disagreement cannot be explained by either the existing or the new theoretical calculations of isospin mixing. If this breakdown can be confirmed by improved experimental data possible reasons, such as enhanced effects of isospin mixing and/or charge-dependent nuclear forces in the fp-shell, should be investigated.

Please read more in the article ... >

10.08.12: Stabilizing shell effects in heaviest elements directly measured

Our division is part of an international research team that has succeeded in directly measuring the strength of shell effects in very heavy elements. The results have just been published in the "Science Express" external Link of the renowned Science magazine. They provide information on the nuclear structure of superheavy elements, thus promising to enable drastically improved predictions concerning the location and extension of the "island of stability" of superheavy elements. Indeed, it is expected that such elements with "magic" numbers of protons and neutrons will profit from enhanced stability due to shell effects, which endow them with long lifetimes. For the present measurements, performed on several isotopes of the elements nobelium und lawrencium, the scientists utilized the Penning trap facility SHIPTRAP external Link at the GSI external Link Helmholtz Centre for Heavy Ion Research in Darmstadt.

Please read more in the article (Science 7 September 2012) ... >

Please read also the following press releases on the successful measurements:

30.06.12: Review article on the occasion of the 100th birthday of Carl Friedrich von Weizsäcker

In "Physik Journal" a review article of Klaus Blaum and Michael Wiescher on the occasion of the 100th birthday of Carl Friedrich von Weizsäcker (1912 – 2007) has just been published. The authors acknowledge and explain two important contributions of C. F. v. Weizsäcker to physics and early cosmology: the Weizsäcker mass formula (1935) and the so-called "Aufbauhypothese" (hypothesis of constitution) on the origin of the elements (1937).
Both scientific findings are still of importance in nuclear physics and nuclear astrophysics. Extended by microscopic corrections, the Weizsäcker mass formula is even today a good approximation for the mass of more than 3000 measured nuclides. This is confirmed by precision mass measurements on short-lived nuclides using modern Penning traps, which is one of the main research topics of Klaus Blaum. Our present understanding of the synthesis of the elements in stars still includes essential aspects of the "hypothesis of constitution". The theoretical physicist Hans Bethe described the supposed CNO cycle (for Carbon, Nitrogen, Oxygen; also Bethe–Weizsäcker cycle), a set of fusion reactions by which stars convert hydrogen to helium, quantitatively.

Please read more in the article ... >

28.06.12: Recent progress in Penning trap design and research

A special issue on ion trapping has just been published in Applied Physics B external Link. Our group contributed three articles about recent progress in Penning trap design and research:

J. Repp et al. report on the novel five-Penning-trap mass spectrometer PENTATRAP, which is developed at the Max-Planck-Institut für Kernphysik (MPIK), Heidelberg. The article gives a motivation for the new mass spectrometer, presents its experimental setup, and describes the present status. The PENTATRAP project aims for ultra high-precision mass-ratio measurements on highly charged, stable, and long-lived ions up to uranium.

Please read more in the article ... >

C. Roux et al. present the design of the novel five-Penning-trap tower for the mass spectrometer PENTATRAP. An analytical expression for the electrostatic potential inside the trap tower has been derived to calculate standard Penning-trap properties like the compensation of anharmonicities and an orthogonal geometry of the trap electrodes. Systematic effects for highly charged ions inside the trap tower have been considered for the design process as well and a limit due to remaining anharmonic shifts at large amplitudes was estimated for the resulting geometry.

Please read more in the article ... >

M. Heck et al. describe the experimental and theoretical investigations of the interaction of stored ions in a Penning trap with one- and two-pulse (Ramsey) quadrupolar excitation fields. The interaction of the ions with the excitation fields has been probed by Fourier transform ion cyclotron resonance (FT-ICR) detection. The theoretical description of this interaction has been derived by use of a quasi-classical coherent state and the interconversion of radial motional modes is interpreted in a quantum-mechanical context.

Please read more in the article ... >

12.06.12: Important step towards the direct determination of the g-factor of a single proton

Charged particles can be stored by a superposition of static magnetic and electric fields in a Penning trap system. A single particle confined in a Penning trap is a suitable system for high-precision measurements of fundamental particle properties and tests of theories. The comparison between the proton and antiproton magnetic moments e.g. provides a very stringent test of charge, parity, time (CPT) symmetry in the baryon sector.

In a just in New Journal of Physics published article C. C. Rodegheri et al. are presenting the cryogenic double Penning trap, which is the core of the experiment for the direct determination of the magnetic moment of a single proton. A complete overview including the trap design, characterization and an optimization method is given. A first attempt at the g-factor determination has been made in a section of the trap with a magnetic bottle of B2 = 300mTmm-2. In this section the detection of spin flips of a single proton could be demonstrated for the very first time. Further improvements allowed to determine the g-factor of 5.585 696(50) with a relative uncertainty of 8.9 ·10-6. This is in excellent agreement with previous measurements and predictions and represents a milestone in the direct determination of the proton magnetic moment with extremely high precision. It brings us closer to the possibility of testing matter–antimatter symmetry at a high precision level in the baryon sector, since the measuring method presented in this paper is also suitable for the determination of the g-factor of the antiproton.
The aim is to achieve a relative uncertainty of 10-9 or better for the g-factor of a single (anti)proton. In order to achieve this, future experiments will drive the spin-flip transition in a section of the trap with a homogeneous magnetic field.

The article has been chosen as " IOP Select external Link ". Please read more ... >

12.05.12: Technical design report of TSR at ISOLDE published

In a just in "The European Physical Journal - Special Topics" published article M. Grieser et al. present the technical design report of the heavy-ion, low-energy ring TSR, which is intended to be setup at the HIE-ISOLDE external Link facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world.
The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for the envisaged purposes. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the technical design report.

Please read more in the article ... >

05.04.12: Shell model for beryllium isotopes invalidated

A young investigator group led by Professor Dr. Wilfried Nörtershäuser, in collaboration with colleagues from the Max Planck Institute of Nuclear Physics in Heidelberg and the KU Leuven, has, for the first time, managed to measure the size of the charge distribution in the atomic nucleus of the highly exotic beryllium-12 isotope. The researchers were surprised to find that the so-called charge radius increases in comparison with that of the beryllium-11 isotope, while the radius of the matter distribution was significantly smaller. These findings contradict the famous shell-model in nuclear physics regarding the structure of atomic nuclei as it was expected that the nuclear charge radius would also be smaller.

Beryllium-12: Dance of the nucleons
Dance of the nucleons: Theoretically, the beryllium-12 nucleus can be seen as a con-glomeration of two helium-4 nuclei with four additional neutrons. Assuming a magic neutron number of N=8, the shell model predicts that, in the beryllium-12 nucleus, all four of these neutrons should be located between the helium-4 nuclei (left). However, the research findings contradict this hypothesis and indicate that two of the neutrons are located outside the helium-4 nuclei. This structure, which more closely resembles the combination of a helium-8 nucleus and a helium-4 nucleus, means that the beryllium nucleus is significantly larger and indicates that the shell-model prediction of N=8 being magic is incorrect for the beryllium-12 nucleus.

The results of the charge radius measurements of 12Be have been published in Physical Review Letters ... >

Detailed information in the press release of the Johannes Gutenberg-Universität Mainz external Link

04.04.12: Junior research grant awarded to our former group member Stefan Ulmer

Our former Ph.D. student and current collaborator obtained a highly competitive research grant – a RIKEN Initiative Research Unit external Link. Within this funding he will set up an experiment for the high precision measurement of the magnetic moment of the antiproton. We are very pleased, that Stefan obtained this funding to continue his research on high precision measurements of the magnetic moment of the (anti)proton.

10.02.12: 110Pd excellent candidate for double-β decay studies

Experimentally observed neutrino oscillations have proved that neutrinos have a finite mass. The study of the rare process of double-β decay is the most promising way to probe the neutrino character and to constrain the neutrino mass.

In a just in Physical Review Letters published article D. Fink et al. report on the first direct mass comparison between 110Pd and the double-β decay daughter nuclide 110Cd. The new measured 110Pd double-β decay Q value of 2017.85(64) keV is shifted by almost 14 keV to the literature value and has a 17 times smaller uncertainty than the AME2003 value. In addition, the absolute masses of 110Pd and 110Cd were determined with high precision, reducing their uncertainties significantly. All measurements were performed with the ISOLTRAP external Link Penningtrap mass spectrometer at ISOLDE/CERN external Link.
The new calculated nuclear matrix element for 110Pd is relatively large compared to most other possible double-β decay nuclides. Thus, in combination with its high natural abundance, 110Pd becomes a very promising candidate for double-β decay studies and for the search for the neutrino mass.

Please read more in the article ... >

Detailed information in the press release of the MPIK external Link

27.01.12: Charge radii of magnesium isotopes appear in PRL
The COLLAPS paper on the charge radii measurements along the magnesium chain has been published as an article in Physical Review Letters. Charge radii along this chain are of particular interest since neutron-deficient isotopes exhibit a cluster-like structure, whereas the neutron-rich isotopes show the transition into the so-called "island of inversion". The radii could only be investigated since we employed for the first time laser-optical pumping combined with particle-sensitive beta-asymmetry detection for isotope shift measurements. This was only possible after a detailled and quantitative understanding of the pumping process and the resulting lineshape was obtained, as it was carried out at COLLAPS external Link over the last couple of years.
The article is available online … >
PRL Editor's Suggestion
The article has been selected as "Editor's Suggestion". This is an award "based on the potential interest in the results presented and, importantly, on the success of the paper in communicating its message, in particular to readers from other fields" (see also here external Link)

23.01.12: Hot molecule explains cold chemistry in free space

Surprisingly, in cold interstellar clouds, hydrogen cyanide, HCN, and the considerably more energetic isomer of hydrogen cyanide, HNC (hydrogen isocyanide), have nearly equal abundance.
In a just in Astrophysical Journal Letters online published article Mario B. Mendes et al. report on experiments that provide an explanation for this phenomenon. These experiments have been performed by the group "Molecular quantum dynamics and stored ion beams" around Andreas Wolf with the ion storage ring at the Max Planck Institute for Nuclear Physics in Heidelberg.

Please read more in the article ... >

Detailed information in the press release of the MPIK external Link

12.01.12: Important progress in the quantitative understanding of H3+

Even after 35 years of activity and despite enormous advances in computers and experimental methods, the spectrum of the smallest triatomic molecular system, the H3+ ion, at higher excitations has remained an enigma neither fully accessed experimentally nor fully elucidated theoretically.

In a just in Physical Review Letters published article M. Pavanello et al. report on new developments that overcome the experimental and theoretical difficulties that occur beyond the barrier to linearity and largely unveil the elusive, highly excited H3+ spectrum.
Experimentally, at the MPI for Nuclear Physics, the sensitivity of ion trap spectroscopy on H3+ has been increased, which now allows to measure the frequencies of ro-vib transitions extending far into the visible spectral range.
The new, precisely measured overtone frequencies gave decisive hints to an international group of molecular theorists on how to dramatically improve their first-principles quantum calculations of this fundamental triatomic molecule. They could obtain a model which reproduces the new observations precisely and is capable of describing the full ro-vib spectrum of H3+.
The described work provides the most accurate global ground-state H3+ potential energy surface (PES) available to date. Together with a simple model for nonadiabatic effects, it is now able to predict the ro-vib transitions of H3+ with unprecedented accuracy.

Please read more in the article ... >

Detailed information also in the press release of the MPIK external Link and the IDW external Link