Klaus Blaum

Masses of exotic calcium isotopes pin down nuclear forces

The properties of exotic nuclei on the verge of existence play a fundamental part in our understanding of nuclear interactions. Exceedingly neutron-rich nuclei become sensitive to new aspects of nuclear forces. Calcium, with its doubly magic isotopes 40Ca and 48Ca, is an ideal test for nuclear shell evolution, from the valley of stability to the limits of existence. With a closed proton shell, the calcium isotopes mark the frontier for calculations with three-nucleon forces from chiral effective field theory. Whereas predictions for the masses of 51Ca and 52Ca have been validated by direct measurements, it is an open question as to how nuclear masses evolve for heavier calcium isotopes. Here we report the mass determination of the exotic calcium isotopes 53Ca and 54Ca, using the multi-reflection time-of-flight mass spectrometer of ISOLTRAP at CERN. The measured masses unambiguously establish a prominent shell closure at neutron number N = 32, in excellent agreement with our theoretical calculations. These results increase our understanding of neutron-rich matter and pin down the subtle components of nuclear forces that are at the forefront of theoretical developments constrained by quantum chromodynamics.

First Penning trap mass measurements beyond the proton drip line.

The masses of six neutron-deficient rare holmium and thulium isotopes close to the proton drip line were determined with the SHIPTRAP Penning trap mass spectrometer. For the first time the masses of the proton-unbound isotopes 144,145Ho and 147,148Tm were directly measured. The proton separation energies were derived from the measured mass values and compared to predictions from mass formulas. The new values of the proton separation energies are used to determine the location of the proton drip line for holmium and thulium more accurately.

Precision atomic physics techniques for nuclear physics with radioactive beams

Atomic physics techniques for the determination of ground-state properties of radioactive isotopes are very sensitive and provide accurate masses, binding energies, Q-values, charge radii, spins and electromagnetic moments. Many fields in nuclear physics benefit from these highly accurate numbers. They give insight into details of the nuclear structure for a better understanding of the underlying effective interactions, provide important input for studies of fundamental symmetries in physics, and help to understand the nucleosynthesis processes that are responsible for the observed chemical abundances in the Universe. Penning-trap and storage-ring mass spectrometry as well as laser spectroscopy of radioactive nuclei have now been used for a long time but significant progress has been achieved in these fields within the last decade. The basic principles of laser spectroscopic investigations, Penning-trap and storage-ring mass measurements of short-lived nuclei are summarized and selected physics results are discussed.

Direct mass measurements above uranium bridge the gap to the island of stability

The mass of an atom incorporates all its constituents and their interactions. The difference between the mass of an atom and the sum of its building blocks (the binding energy) is a manifestation of Einstein’s famous relation E = mc2. The binding energy determines the energy available for nuclear reactions and decays (and thus the creation of elements by stellar nucleosynthesis), and holds the key to the fundamental question of how heavy the elements can be. Superheavy elements have been observed in challenging production experiments, but our present knowledge of the binding energy of these nuclides is based only on the detection of their decay products. The reconstruction from extended decay chains introduces uncertainties that render the interpretation difficult. Here we report direct mass measurements of trans-uranium nuclides. Located at the farthest tip of the actinide species on the proton number–neutron number diagram, these nuclides represent the gateway to the predicted island of stability. In particular, we have determined the mass values of 252-254No (atomic number 102) with the Penning trap mass spectrometer SHIPTRAP. The uncertainties are of the order of 10 keV/c2 (representing a relative precision of 0.05 p.p.m.), despite minute production rates of less than one atom per second. Our experiments advance direct mass measurements by ten atomic numbers with no loss in accuracy, and provide reliable anchor points en route to the island of stability.

High-precision measurement of the atomic mass of the electron

The quest for the value of the electron’s atomic mass has been the subject of continuing efforts over the past few decades. Among the seemingly fundamental constants that parameterize the Standard Model of physics and which are thus responsible for its predictive power, the electron mass me is prominent, being responsible for the structure and properties of atoms and molecules. It is closely linked to other fundamental constants, such as the Rydberg constant R∞ and the fine-structure constant α (ref. 6). However, the low mass of the electron considerably complicates its precise determination. Here we combine a very precise measurement of the magnetic moment of a single electron bound to a carbon nucleus with a state-of-the-art calculation in the framework of bound-state quantum electrodynamics. The precision of the resulting value for the atomic mass of the electron surpasses the current literature value of the Committee on Data for Science and Technology (CODATA) by a factor of 13. This result lays the foundation for future fundamental physics experiments and precision tests of the Standard Model.

TRIGA-SPEC: A setup for mass spectrometry and laser spectroscopy at the research reactor TRIGA Mainz

Abstract The research reactor TRIGA Mainz is an ideal facility to provide neutron-rich nuclides with production rates sufficiently large for mass spectrometric and laser spectroscopic studies. Within the TRIGA-SPEC project, a Penning trap as well as a beamline for collinear laser spectroscopy are being installed. Several new developments will ensure high sensitivity of the trap setup enabling mass measurements even on a single ion. Besides neutron-rich fission products produced in the reactor, also heavy nuclides such as 235 U or 252 Cf can be investigated for the first time with an off-line ion source. The data provided by the mass measurements will be of interest for astrophysical calculations on the rapid neutron-capture process as well as for tests of mass models in the heavy-mass region. The laser spectroscopic measurements will yield model-independent information on nuclear ground-state properties such as nuclear moments and charge radii of neutron-rich nuclei of refractory elements far from stability. TRIGA-SPEC also serves as a test facility for mass and laser spectroscopic experiments at SHIPTRAP and the low-energy branch of the future GSI facility FAIR. This publication describes the experimental setup as well as its present status.

Penning traps as a versatile tool for precise experiments in fundamental physics

This review article describes the trapping of charged particles. The main principles of electromagnetic confinement of various species from elementary particles to heavy atoms are briefly described. The preparation and manipulation with trapped single particles, as well as methods of frequency measurements, providing unprecedented precision, are discussed. Unique applications of Penning traps in fundamental physics are presented. Ultra-precise trap-measurements of masses and magnetic moments of elementary particles (electrons, positrons, protons and antiprotons) confirm CPT-conservation, and allow accurate determination of the fine-structure constant α and other fundamental constants. This together with the information on the unitarity of the quark-mixing matrix, derived from the trap-measurements of atomic masses, serves for assessment of the Standard Model of the physics world. Direct mass measurements of nuclides targeted to some advanced problems of astrophysics and nuclear physics are also presented.

Ramsey method of separated oscillatory fields for high-precision penning trap mass spectrometry

Ramseys method of separated oscillatory fields is applied to the excitation of the cyclotron motion of short-lived ions in a Penning trap to improve the precision of their measured mass values. The theoretical description of the extracted ion-cyclotron-resonance line shape is derived and its correctness demonstrated experimentally by measuring the mass of the short-lived 38Ca nuclide with an uncertainty of 1.1 x 10(-8) using the Penning trap mass spectrometer ISOLTRAP at CERN. The mass of the superallowed beta emitter 38Ca contributes for testing the theoretical corrections of the conserved-vector-current hypothesis of the electroweak interaction. It is shown that the Ramsey method applied to Penning trap mass measurements yields a statistical uncertainty similar to that obtained by the conventional technique but 10 times faster. Thus the technique is a new powerful tool for high-precision mass measurements.

HITRAP: A Facility at GSI for Highly Charged Ions

Abstract An overview and status report of the new trapping facility for highly charged ions at the Gesellschaft fur Schwerionenforschung is presented. The construction of this facility started in 2005 and is expected to be completed in 2008. Once operational, highly charged ions will be loaded from the experimental storage ring ESR into the HITRAP facility, where they are decelerated and cooled. The kinetic energy of the initially fast ions is reduced by more than fourteen orders of magnitude and their thermal energy is cooled to cryogenic temperatures. The cold ions are then delivered to a broad range of atomic physics experiments.

Direct Mapping of Nuclear Shell Effects in the Heaviest Elements

Pinning Down Nuclear Shells The nuclei of heavy atoms are destabilized by proton repulsions, and, conversely, the quantum-mechanical shell effects help to stabilize them. There are theoretical models for predicting the masses of yet-to-be-discovered superheavy elements, based on such shell effects, and these models can be tested by studying the shells of known actinide nuclei. The problem is that current mass values determined from studying radioactive decay products have substantial errors. Minaya Ramirez et al. (p. 1207, published online 9 August; see the Perspective by Bollen) were able to collect a sufficient number of nuclei of lawrencium and nobelium isotopes in an ion trap to determine their masses directly by mass spectroscopy. These results will be helpful in predicting the heaviest possible element. Highly precise mass measurements of nobelium and lawrencium isotopes provide insight into superheavy element stability. Quantum-mechanical shell effects are expected to strongly enhance nuclear binding on an “island of stability” of superheavy elements. The predicted center at proton number Z = 114, 120, or 126 and neutron number N = 184 has been substantiated by the recent synthesis of new elements up to Z = 118. However, the location of the center and the extension of the island of stability remain vague. High-precision mass spectrometry allows the direct measurement of nuclear binding energies and thus the determination of the strength of shell effects. Here, we present such measurements for nobelium and lawrencium isotopes, which also pin down the deformed shell gap at N = 152.