A. Kellerbauer

A linear radiofrequency ion trap for accumulation, bunching, and emittance improvement of radioactive ion beams

An ion beam cooler and buncher has been developed for the manipulation of radioactive ion beams. The gas-filled linear radiofrequency ion trap system is installed at the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. Its purpose is to accumulate the 60-keV continuous ISOLDE ion beam with high efficiency and to convert it into low-energy low-emittance ion pulses. The efficiency was found to exceed 10% in agreement with simulations. A more than 10-fold reduction of the ISOLDE beam emittance can be achieved. The system has been used successfully for first on-line experiments. Its principle, setup and performance will be discussed.

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.

Recent developments at ISOLTRAP: Towards a relative mass accuracy of exotic nuclei below 10-8

During the last two years, the performance of the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN (Geneva) has been considerably enhanced. Many technical improvements have been completed (i) to access nuclides that are produced in minute quantities of only 100 ions s−1, (ii) to increase the relative mass accuracy to ≤ 1 × 10−8 and (iii) to make accessible nuclei with a half-life of down to ≈ 5 ms. The major steps are presented, in particular the recent implementation of a magnetron phase locking mechanism which results in a significant reduction of the duration of ISOLTRAPs cyclotron measurements.

Exploring the WEP with a pulsed cold beam of antihydrogen

The AEGIS experiment, currently being set up at the Antiproton Decelerator at CERN, has the objective of studying the free fall of antimatter in the Earth?s gravitational field by means of a pulsed cold atomic beam of antihydrogen atoms. Both duration of free fall and vertical displacement of the horizontally emitted atoms will be measured, allowing a first test of the WEP with antimatter.

Buffer gas cooling of ion beams

Abstract The cooling action of a buffer gas on ions contained within it can be used to cool an ion beam, thereby greatly improving its emittance and energy spread. It can also be used to greatly enhance the collection of an ion beam in an electromagnetic trap. The basic principles will be introduced in the context of a prototype system for such a beam cooler.

Mass measurements beyond the major r-process waiting point 80Zn

High-precision mass measurements on neutron-rich zinc isotopes (71m,72-81)Zn have been performed with the Penning trap mass spectrometer ISOLTRAP. For the first time, the mass of 81Zn has been experimentally determined. This makes 80Zn the first of the few major waiting points along the path of the astrophysical rapid neutron-capture process where neutron-separation energy and neutron-capture Q-value are determined experimentally. The astrophysical conditions required for this waiting point and its associated abundance signatures to occur in r-process models can now be mapped precisely. The measurements also confirm the robustness of the N=50 shell closure for Z=30.

High-precision mass measurements of nickel, copper, and gallium isotopes and the purported shell closure at N=40

High-precision mass measurements of more than 30 neutron-rich nuclides around the Z=28 closed proton shell were performed with the triple-trap mass spectrometer ISOLTRAP at ISOLDE/CERN to address the question of a possible neutron shell closure at N=40. The results for {sup 57,60,64-69}Ni (Z=28), {sup 65-74,76}Cu (Z=29), and {sup 63-65,68-78}Ga (Z=31) have a relative uncertainty of the order of 10{sup -8}. In particular, the mass of {sup 76}Cu was measured for the first time. We analyze the resulting mass surface for signs of magicity, comparing the behavior of N=40 with that of known magic numbers and with midshell behavior. While the classic indications from the mass surface show no evidence for a shell closure at N=40, there is evidence for a weak--and very localized--effect for Z=28, consistent with findings from nuclear spectroscopy studies.

Mass measurements and nuclear physics-recent results from ISOLTRAP

The Penning trap mass spectrometer ISOLTRAP is a facility for high-precision mass measurements of short-lived radioactive nuclei installed at ISOLDE/CERN in Geneva. More than 200 masses have been measured with relative uncertainties of 1 × 10−7 or even close to 1 × 10−8 in special cases. This publication gives an overview of the measurements performed with ISOLTRAP and discusses some results.

A moiré deflectometer for antimatter

The precise measurement of forces is one way to obtain deep insight into the fundamental interactions present in nature. In the context of neutral antimatter, the gravitational interaction is of high interest, potentially revealing new forces that violate the weak equivalence principle. Here we report on a successful extension of a tool from atom optics—the moiré deflectometer—for a measurement of the acceleration of slow antiprotons. The setup consists of two identical transmission gratings and a spatially resolving emulsion detector for antiproton annihilations. Absolute referencing of the observed antimatter pattern with a photon pattern experiencing no deflection allows the direct inference of forces present. The concept is also straightforwardly applicable to antihydrogen measurements as pursued by the AEgIS collaboration. The combination of these very different techniques from high energy and atomic physics opens a very promising route to the direct detection of the gravitational acceleration of neutral antimatter.

Evidence for a breakdown of the isobaric multiplet mass equation: A study of the A = 35,T = 3/2 isospin quartet

The application of the isospin formalism in nuclear physics stems from the assumption that the strong interaction is almost charge-independent. In addition to the approximation that the neutron and the proton have the same mass, the isospin formalism describes the neutron and the proton as identical particles with isospin T = 1/2 with the projections Tz(n) = +1/2 and Tz(p) = −1/2, respectively [1, 2]. Isobaric nuclei with the same isospin T belong to a 2T +1 multiplet with the projections Tz = (N −Z)/2, where N is the number of neutrons and Z the number of protons in the nucleus. The correspond—