News Archive 2014

10.12.14: First application of highly sensitive β-NMR spectroscopy for a species in solution

Nuclear magnetic resonance (NMR) spectroscopy is currently the most versatile spectroscopic technique for the characterization of molecular structure and dynamics in solution. However, the conventional NMR spectroscopy has considerably limited sensitivity. To record a conventional NMR spectrum >10¹⁶ of probe nuclei are typically required. Thus, novel spectroscopic techniques with significantly enhanced sensitivity are required.
β-NMR spectroscopy is highly sensitive compared to conventional NMR spectroscopy. It has previously been successfully applied in the fields of nuclear and solid-state physics. Besides its extreme sensitivity β-NMR spectroscopy allows access to elements that are difficult to detect in solution by using conventional NMR, such as Mg and potentially Cu.

In a recently in ChemPhysChem published article A. Gottberg et al. report on the first application of β-NMR spectroscopy to an ionic-liquid solution containing Mg²⁺ ions. For this experiment, a novel prototype on-line setup of the COLLAPS collaboration was used, specifically designed for liquid samples at the CERN-ISOLDE facility in Geneva. In distinction to conventional NMR, in β-NMR the nuclei are polarized prior to implantation into the sample and the resonance detection relies on the detection of β-particles from the decay of radioactive nuclei, and thus benefits from the high sensitivity of radiotracer experiments. In the described experiment ³¹Mg β-NMR spectra could be measured for as few as 10⁷ magnesium ions in ionic liquid (EMIM-Ac: 1-ethyl-3-methyl-imidazolium acetate) within minutes, as a prototypical test case. Resonances were observed at 3882.9 and 3887.2 kHz in an external field of 0.3 T.
The demonstrated highly sensitive β-NMR spectroscopy has proved to be suited for the analysis of species in solution. It can be used as a novel spectroscopic technique in general chemistry and potentially in biochemistry.

Please read more in the article ... >

02.10.14: Einstein's special theory of relativity precisely confirmed

An international cooperation of physicists with the participation of our division successfully performed the most precise direct measurement of the relativistic time dilation using the optical Doppler effect. The result is a further precise confirmation of Einstein's special theory of relativity.
Please read more in the Physical Review Letters article ... >
More information in the detailed press release of the MPIK .

Further press releases:

Nature News: Special relativity aces time trial
Physics Synopsis: Relativity is Right on Time, Again
Spektrum.de: Relativitätstheorie besteht Test
Frankfurter Allgemeine Zeitung: Einsteins Triumph: Relativitätstheorie auf dem Prüfstand
Science 2.0: Time Dilation And Quantum Electrodynamics – Einstein Wins Again

30.09.14: Progress in nuclear structure studies beyond the N=28 shell gap

Nowadays a large variety of exotic nuclei can be produced and studied with the highest precision. The experimental data of such nuclei with large N/Z ratio show that the original shell gaps predicted by the more than 60-year-old shell model are not preserved and "new" shell closures appear. In the past decade, the region below Ca (Z < 20) with 20 ≤ N ≤ 28 was investigated intensively and the experimental results were compared to shell-model calculations up to N = 28. Potassium isotopes with only one proton less than the magic number Z = 20 are excellent probes to study the shell model. For the neutron-rich potassium isotopes, little and especially conflicting information is available so far, thus this important region of the nuclear chart has to be extensively studied.

In a recent article published in Physical Review C J. Papuga et al. report on high-resolution collinear laser spectroscopy of neutron-rich potassium isotopes at COLLAPS at ISOLDE /CERN, Geneva. The hyperfine structure spectra yielded the nuclear spins and magnetic moments of the ground states of the K isotopes. The measured magnetic moments are in good agreement with shell-model calculations using SDPF-NR and SDPF-U effective interactions. Since ground-state spins and magnetic moments are sensitive to the nuclear wave function, they are powerful probes to study the structure of the exotic nuclei. The measured potassium chain from N = 19 up to N = 32 is of great interest, since it has a hole in the πsd orbital and it covers two major neutron shells, N = 20 and N = 28, and one subshell at N = 32.
The experiment especially aimed to extend the knowledge about the evolution of the 1/2⁺ and 3/2⁺ states for K isotopes beyond the N = 28 shell gap. The observed inversion of the nuclear spin from I = 3/2 to I = 1/2 at N = 28 (^47,49K) and the reinversion back to I = 3/2 at N = 32 (⁵¹K) can theoretically be explained by the evolution of the proton orbitals (πsd) while different neutron orbitals are being filled.
The presented experimental results of the neutron-rich potassium isotopes contribute to future improvements of the effective shell-model interactions and ab initio calculations.

Please read more in the article ... >

24.09.14: First extensive test of a Partial Dynamical Symmetry for atomic nuclei

Symmetries in nature are widespread and fundamental to modern science since they offer very simple descriptions of complex systems. In nuclear physics symmetries are mathematically described by group theory and the symmetry groups such as the special unitary group of degree 3 SU(3). Dynamical Symmetries (DSs) aim at describing the astonishingly regular and simple patterns exhibited by complex many-body correlated systems. DS are successfully used to describe nuclear structure in the context of the interacting boson approximation (IBA) model. However, the vast majority of nuclei deviate from any DS and thus recently so called Partial Dynamical Symmetries (PDS) which break the DSs while preserving important symmetry remnants, are studied. They suggest a potentially more widespread role of symmetries in nuclei.

In a recently in Physical Review Letters published article R. F. Casten et al. present the first extensive test of a Partial Dynamical Symmetry for nuclei. SU(3) PDS predictions have been compared with the data on the gamma to ground state band B(E2) transition rates covering 47 even-even nuclei in the rare earth region, especially ¹⁶⁸Er. In the article the agreement of parameter-free SU(3) PDS with the E2 transition data as well as the characteristic discrepancies are discussed. The found evidence for PDS in atomic nuclei suggests a much wider applicability of dynamical symmetries and encourages detailed tests of other PDSs.

Please read more in the article ... >

31.07.14: First observation of increase in nuclear charge radius between ground and isomeric state of ³⁸K

In nuclear physics an isomer is the metastable excited state of an atomic nucleus. Nuclear ground and isomeric state of an atomic nucleus have different charge distributions which causes a shift of their atomic spectral lines, the so called isomer shift. Thus, the difference of the nuclear charge radii between ground and isomeric state can be determined through the measurement of the isomer shift. This provides a highly sensitive test of modern nuclear structure calculations.

In a recently in Physical Review Letters published article M. L. Bissell et al. report on a high-precision measurement of the isomer shift between ground and isomeric state of the self-conjugate nucleus ³⁸K using bunched-beam collinear laser spectroscopy at CERN-ISOLDE , Geneva. The change in the mean-square charge radius of the metastable ³⁸K^m (I^π = 0⁺) compared to the ground state ³⁸K^g (I^π = 3⁺) was determined to be +0.100(6) fm². This direct measurement is an order of magnitude more accurate than the result of a previous indirect measurement. In this experiment Behr et al. found in 1997 in contrast to the new direct measurement that, within errors, both long-lived states in ³⁸K have similar charge radii. Furthermore, they concluded from a detailed calculation that the ground state of ³⁸K should be larger than the isomer by 0.014 fm², which is contradictory to the directly measured difference.

M. L. Bissell et al. demonstrate in their article that the directly determined direction and magnitude of the isomer shift resp. the increase in mean square charge radius in ³⁸K^m can be described phenomenologically when proton-neutron pairing correlations are considered in analogy to proton-proton and neutron-neutron pairing correlations.

Please read more in the article ... >

04.07.14: New method allows first mass measurement of the short-lived nuclide ⁵¹Co

Ion storage rings are versatile facilities ideally suited for performing high precision measurements of masses of short-lived nuclides. Since the masses of exotic nuclei are indispensable quantities for nuclear structure and astrophysics as well as for investigations of fundamental symmetries, huge efforts are undertaken worldwide, both in theory and experiment, to extend the knowledge of their masses. Very sensitive and fast techniques are applied, e.g. the isochronous mass spectrometry (IMS) which was pioneered at the experimental storage ring (ESR) facility of GSI Darmstadt.

In the isochronous mode of a storage ring the revolution time of ions with identical mass-over-charge ratio is independent of their velocity. The revolution time difference of a stored ion with respect to a reference time is directly related to its mass-over-charge ratio difference. Thus, for a mass measurement it is required to achieve accurate determination of revolution times (frequencies) of stored ions. Ions with identical mass-over-charge ratios cannot be resolved in a storage ring.

In a recently in Physics Letters B published article P. Shuai et al. present a new method which allows for the resolution of ions with identical mass-over-charge ratios in a storage ring. The experiment was performed at the HIRFL-CSR accelerator complex in the Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS), with the combination of a heavy ion synchrotron CSRm, an in-flight fragment separator RIBLL2 and the experimental storage ring CSRe. The isochronous mass spectrometry was applied on ⁵⁸Ni projectile fragments, especially ⁵¹Co²⁷⁺ and ³⁴Ar¹⁸⁺.

Since the mass-over-charge ratios of ⁵¹Co²⁷⁺ and ³⁴Ar¹⁸⁺ ions are almost identical they cannot be resolved by their revolution times. But they have different signal amplitudes due to a difference of ion energy loss in the detector foil, which scales in first order with q². This charge dependence was employed to resolve the peaks of ⁵¹Co²⁷⁺ and ³⁴Ar¹⁸⁺ ions and to extract their revolution times which allowed to determine their masses. The re-determined mass excess for ³⁴Ar ME(³⁴Ar) = −18 379(15) keV is in excellent agreement with the independently measured value of F. Herfurth et al. (2001). The mass excess of ⁵¹Co was determined for the first time to be ME(⁵¹Co) = −27 342(48) keV. The new mass of ⁵¹Co is essential for investigating the importance of isospin-nonconserving (INC) interactions in the fp-shell nuclei.

Please read more in the article ... >

03.07.14: TRIGA-TRAP mass measurements on transuranium nuclides in the vicinity of the deformed N=152 neutron shell closure

Superheavy nuclides owe their existence purely to quantum-mechanical shell effects which become more important in heavy nuclei as they can enhance nuclear lifetimes tremendously near the shell closures. The so called "island of stability" of superheavy nuclei is predicted near the next spherical shell closure beyond the doubly magic nuclei ²⁰⁸Pb. Its location in the nuclear landscape has been predicted to be at differentproton numbers, some favoring Z = 114, while others prefer Z = 120 or 126.

In the past years, nuclear structure studies benefited from direct high-precision Penning-trap mass measurements of radioactive nuclides in the neutron-rich and deficient region as well as in the region of the heaviest elements. Especially efforts at the SHIPTRAP facility at GSI Darmstadt allowed to establish new anchor points in α-decay chains reducing the influence of nuclear transition energy measurements on the masses of superheavy nuclides. More experimental data is needed to pin down the exact location of the "island of stability".

In a recent article published in Physical Review C M. Eibach et al. report on direct high-precision mass measurements of four transuranium nuclides, ^241,243Am, ²⁴⁴Pu, and ²⁴⁹Cf, in the vicinity of the deformed N = 152 neutron shell closure. The measurements were performed with the double Penning-trap mass spectrometer TRIGA-TRAP which is part of the TRIGA-SPEC experiment at the research reactor TRIGA Mainz . At TRIGA-TRAP, ions are produced in a newly developed laser ablation ion source combined with a buffer-gas filled miniature radio frequency quadrupole structure, and captured in two Penning traps. At first they are stored in a cylindrical Penning trap for mass selective buffer-gas cooling with helium in order to reduce the motional amplitudes and to select the ion of interest. Subsequently, they are transferred to the hyperbolical Penning trap to perform the mass measurement. The measurement is based on the free cyclotron frequency ν_c determination of the ion with charge-to-mass ratio q/m stored in a B = 7 T strong magnetic field. For this purpose the time-of-flight ion-cyclotron-resonance technique (TOF-ICR) is used employing a Ramsey excitation profile. The flight time of the ions to an MCP detector outside the magnetic field is measured as function of the excitation frequency. Carbon cluster ions are used as mass references.

The TRIGA-TRAP measurement results confirm the mass values of ^241,243Am and ²⁴⁴Pu of the most recent Atomic-Mass Evaluation "AME2012" within one standard deviation. In the case of the ²⁴⁹Cf mass, a discrepancy of more than three standard deviations has been observed, affecting absolute masses even in the superheavy element region. The implementation of the mass values into the AME2012 network yields a reduced mass uncertainty for 84 nuclides.

Please read more in the article ... >

28.05.14: Double Penning-trap technique allows investigation of matter-antimatter imbalance

The observable universe is matter-dominated. Since every particle is produced with its corresponding antiparticle and such particle-antiparticle pairs annihilate each other matter particles needed to have outnumbered antimatter particles immediately after the creation of the universe. As a result all antimatter particles were destroyed, leaving behind only matter. The fundamental Charge, Parity, and Time Reversal (CPT) symmetry of the Standard Model of particle physics implies the exact equality between the properties of a particle and its antiparticle. Therefore, the measurement of minutest differences between the properties of e.g. a proton and its corresponding antiparticle, the antiproton, could help to explain the matter-antimatter imbalance of our universe.

One of the fundamental properties of the proton is its magnetic moment, μ_p. The direct high-precision comparison of the magentic moments of the proton and the antiproton provides a precise test of the particle-antiparticle equality in the baryonic sector.
So far the most precise value of μ_p with a precision of 10 p.p.b has been obtained indirectly in 1972 by analysing the spectrum of an atomic hydrogen maser in a magnetic field.
Direct measurements of magnetic moments of single electrons resp. positrons in Penning traps have already been applied with great success in 1987. The application of Penning traps to measure the magnetic moment of a single proton is a considerable challenge, because μ_p is about 700 times smaller than μ_e. The determination of the magnetic moment of a single proton in a Penning trap is based on the measurement of the frequency ratio of the Larmor frequency (ν_L) and the cyclotron frequency (ν_c). ν_c is obtained by the invariance theorem and ν_L can be measured by application of the so-called continuous Stern–Gerlach-effect. Therefore a very large magnetic field inhomogeneity (magnetic bottle) is superimposed to the trap, which couples the spin magnetic moment of the proton to its axial oscillation frequency. Such direct measurements of μ_p in a Penning trap with a magnetic bottle were performed in 2012. However, the magnetic bottle broadens the Larmor resonance line significantly, and thus, limits the experimental precision, which is lower than the precision of the mentioned indirect determination method.

In a recently in the journal "Nature" published letter A. Mooser et al.report on the direct high-precision measurement of the magnetic moment of the proton at University of Mainz, Germany. In order to reduce the broadening of the Larmor resonance a double Penning-trap setup has been developed. It consists of two separate Penning traps, an analysis trap and a precision trap, which are connected by transport electrodes. The spin-state detection is carried out in the analysis trap with the superimposed strong magnetic bottle. The measurement of the cyclotron frequency and the excitation of spin-flips at the Larmor frequency are performed in the precision trap, in which the magnetic field is more homogeneous by orders of magnitude. This narrows the width of the Larmor resonance dramatically, and thus this elegant double Penning-trap method significantly improves the precision. The result of the double Penning-trap experiment of A. Mooser et al. is 3 times more precise than the 42-year-old value of the indirect method and about 760 times more precise than other direct single proton Penning-trap measurements.

The described double Penning-trap method can also be applied to measure the antiproton magnetic moment with similar precision. A comparison of both values will provide a sensitive test of CPT invariance with baryons. The measurement of the antiproton magnetic moment will be conducted at the BASE experiment at the Antiproton Decelerator of CERN, Geneva.

Please read more in the "Nature" letter ... >

Further information in the press releases of the Max Planck Society , the MPIK , the University of Mainz , the GSI Darmstadt , the RIKEN institute , the CERN Courier , and the article of "Nature" News .

Further press releases:

24.03.14: Article included in the "Highlights of 2013" of Physica Scripta

The article "Precision atomic physics techniques for nuclear physics with radioactive beams" written by Klaus Blaum, Jens Dilling and Wilfried Nörtershäuser has been selected by the editors of "Physica Scripta" for inclusion in the exclusive "Highlights of 2013" collection. Articles are chosen by Physica Scripta for the Highlights collection on the basis of referee endorsement, novelty, scientific impact and broadness of appeal.

The honored article is one of the most influential research works published in the journal in the year 2013. It is based on the contributions of the authors to the Nobel Symposium on “Physics with Radioactive Beams” in Göteborg, Sweden, June 10-15, 2012. In the article the basic principles of Penning-trap and storage-ring mass spectrometry as well as laser spectroscopy of radioactive nuclei are summarized. Further the significant progress in these fields within the last decade and selected physics results from which many areas in nuclear physics benefit are described.

Links:

03.03.14: First insight into evolution of nuclear size above N=28

Mean square charge radii of nuclei in the calcium region (Z=20) have been the subject of extensive investigation, both experimentally and theoretically. To date very little is known on the nuclei above neutron number N=28. In this region substantial structural changes are predicted, e.g the the development of subshell closures at N=32 and N=34. It is currently little known how the nuclear charge radii would be influenced by the anticipated structural evolution in the region beyond N=28.

In a recently in Physics Letters B published article K. Kreim et al. report on the measurement of optical hyperfine structure and isotope shifts for ^{38,39,42,44,46–51}K relative to ⁴⁷K. The measurements were carried out at the collinear laser spectroscopy setup COLLAPS at ISOLDE -CERN, Geneva. From the results changes in the nuclear mean square charge radii were deduced.

In the region of the isotopic chains below N=28 the behavior of the root mean square (rms) charge radii displays a surprisingly strong dependence on the atomic number Z. To date, no single theoretical model has fully described this behavior. According shell-model calculations up to N=28 the protons and neutrons in the calcium region occupy the same orbitals resulting in a complex interplay of proton and neutron configurations. Above N=28 the changes in mean square radii show little or no dependence on Z. The present measurement data do not allow any conclusion on a possible shell closure at N=32. The results of the rms charge radii were compared to theoretical calculations considering non-relativistic and relativistic mean field (MF) approaches. Neither model can reproduce the measured parabolic shape between N=20 and 28.

The performed hyperfine structure and isotope-shift measurements extended the now accessible range of K isotopes to the neutron numbers N=18–32 and revealed the remarkable described difference in the behavior of the root mean square charge radii below and above N=28.

Please read more in the article ... >

20.02.14: High-precision measurement of the electron mass

In a recently in the prestigious scientific journal "Nature" published article our division members S. Sturm et al. report on the high-precision measurement of the atomic mass of the electron. The precise determination of the electron mass is a result of the close cooperation of physicists of the Max Planck Institute for Nuclear Physics, the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, and the Johannes Gutenberg University Mainz.

The accurate values of fundamental constants depend on the precise knowledge of the electron mass. An important example is the fine structure constant alpha which determines the shape and the properties of atoms and molecules. The electron mass is a central quantity in the Standard Model of particle physics which is incomplete. Thus, the precise knowledge of the electron mass is crucial to explore "new physics".

How can we precisely weigh the punctual electron? Each weighing is based on the use of a mass reference for comparison. In the case of the electron the physicists use the bare nucleus of the carbon (C)-12 isotope. Since the C-12 mass is precisely known by definition, it is the ideal mass reference. In the experiment the physicists coupled a single electron with a C-12 nucleus. The resulting carbon ion was stored in a Penning trap. The extremely homogeneous magnetic field inside the Penning trap forces the carbon ion to move on a circular orbit. In the strong magnetic field the electron spin shows a precessional motion like a tiny spinning top. The revolution frequency (cyclotron frequency) of the carbon ion in the Penning trap and the frequency of the electron precession (Larmor frequency) show a defined relation. Both experimentally determined frequencies yield the so called g-factor or gyromagnetic factor, which in turn allows for the determination of the electron mass.

Theorists from Heidelberg around Zoltan Harman from the theory group of Christoph Keitel succeeded in calculating the g-factor more precisely than ever before. This allowed the accurate determination of the electron mass.

In accordance with the latest measurements the electron weighs 1/(1836,15267377) of the proton mass which is nearly 10^-30 kilograms. The electron mass is now known exactly on eleven places after the decimal point. The research cooperation around the physicists from Heidelberg thus has succeeded in improving the determination of the value of the electron mass by a factor of 13.

Please read more in the "Nature" article ... >

Further information:

11.02.14: Frontiers of ion trap and atomic physics

In 1989 the Nobel Prize in Physics was awarded to Wolfgang Paul and Hans Dehmelt "for the development of the ion trap technique," which has led to a dramatic development of atomic precision spectroscopy in the 1980s. In August 2013, Wolfgang Paul would have celebrated his 100th birthday. In order to commemorate this date, a special volume of "Applied Physics B" dedicated to ion trap physics has recently been published.
Our division contributed five articles to the special volume. Its contributions clearly show the active ongoing research with ion traps:

A. Chaudhuri et al. present an overview of direct mass measurements of short-lived nuclides using TITAN, a Penning trap mass spectrometer facility at TRIUMF, Canada, particularly suitable for precision measurements of ms-half-life nuclides.

Please read more in the article ... >

S. Eliseev et al. present a novel approach to mass measurements at the 10^-9 level for short-lived nuclides with half-lives well below one second at SHIPTRAP, GSI, Darmstadt. The phase-imaging technique is based on the projection of the radial ion motion in a Penning trap onto a position-sensitive detector. Compared with the presently employed time-of-flight ion-cyclotron-resonance technique, the novel approach is 25-times faster and provides a 40-fold gain in resolving power.

Please read more in the article ... >

T. Beyer et al. present a technical description and the characterization with stable ions of a linear Paul trap for cooling of ion beams, the former cooler for emittance elimination radiofrequency quadrupole (RFQ) at MISTRAL/ISOLDE, CERN. It has been installed and commissioned at the TRIGA-SPEC experiment located at the research reactor TRIGA Mainz and allows delivery of low-emittance ion bunches to TRIGA-TRAP and TRIGA-LASER.

Please read more in the article ... >

S. Streubel et al. present the improvements, current status and future perspectives of the THe-Trap experiment at the Max Planck Institute for Nuclear Physics, Heidelberg which is intended to measure the tritium/helium-3 mass ratio in order to deduce the Q value of the tritium β-decay. The Q value is of relevance for the Karlsruhe Tritium Neutrino (KATRIN) collaboration, which is building a spectrometer to measure the mass of the electron antineutrino.

Please read more in the article ... >

M. Rosenbusch et al. present a purification method for "contaminations" of ion sources. Such unwanted ions of masses similar to those of the ions of interest are handicapping the success of many measurements in analytical mass spectrometry as well as in precision mass determinations for atomic and nuclear physics. Proof-of-principle demonstrations have been performed with the ISOLTRAP setup at ISOLDE/CERN.

Please read more in the article ... >

10.02.14: Improved understanding of formation and destruction of greenhouse gas SF₆

Owing to its large capture cross section for electrons, sulfur hexafluoride (SF₆) is commonly used in high-voltage equipments and accelerators as a gaseous dielectric and as a plasma etching gas. For these applications and also to understand the degradation of the harmful greenhouse gas SF₆ from the Earth’s atmosphere, the formation of SF₆^- anions and their destruction is of paramount interest.

In a recently in Physical Review A published article S. Menk et al. report on vibrational autodetachment (VAD) measurements of hot SF₆^- anions. The SF₆^- anions were stored in the extremely high vacuum of the cryogenic electrostatic ion beam trap (CTF) located at the Max-Planck-Institute for Nuclear Physics, Germany. The extremely low residual gas densities of 10⁴ cm^-3 provided undisturbed observation of the neutralization rates due to VAD over almost five orders of magnitude and over times up to 100 ms. This allowed to investigate the VAD process of the excited SF₆^- anions in the so far not accessible long-time and low-intensity limit.

The experimental data could be successfully reproduced by using statistical rate theory when accounting for the C_4ν distortion of SF₆^-. The unprecedented sensitivity of the experiment to the decay constants at the VAD threshold allowed to infer from the data the adiabatic electron affinity of SF₆ to be (0.91 ± 0.07) eV and to confirm the recently predicted C_4ν symmetry of SF₆^-.

Please read more in the article ... >