Gerrit Marx

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.

The SHIPTRAP project: A capture and storage facility at GSI for heavy radionuclides from SHIP

SHIPTRAP is an ion trap facility which is being set up to deliver very clean and cool beams of singly-charged recoil ions produced at the SHIP velocity filter at GSI Darmstadt. SHIPTRAP consists of a gas cell for stopping and thermalizing high-energy recoil ions from SHIP, a rf ion guide for extraction of the ions from the gas cell, a linear rf trap for accumulation and bunching of the ions, and a Penning trap for isobaric purification. The physics programme of the SHIPTRAP facility comprises mass spectrometry, nuclear spectroscopy, laser spectroscopy and chemistry of transeinsteinium elements.

Atomic clusters and ion-cyclotron-resonance mass spectrometry: a fruitful combination

Clusters consisting of a few atoms build the bridge between individual atoms and the condensed phase of matter and they are, thus, of great general interest. Over the last two decades, considerable progress has been made in the study of their properties and ion storage techniques, in particular the use of ion cyclotron resonance (Penning) traps, are important tools for advanced investigations. Vice versa, cluster ions can serve as probes for the evaluation of ion-trap properties. Furthermore, they are ideally suited for the calibration of mass spectrometers and for consistency checks in high-accuracy mass determinations. Examples from the research areas mentioned, i.e. the investigation of cluster properties and the application of cluster ions for Penning-trap studies and mass calibration, are reported.

Atomic clusters in a Penning trap: investigation of their properties and utilization as diagnostic tools

Ion traps are useful tools for many investigations on charged molecules and clusters. At ClusterTrap, the Penning trap is more than just a storage device. The split-ring electrodes allow radial excitations of the trapped-ion motion such that the ions can be centred in the trap or ejected from it, thus allowing the study of size-selected charged clusters. The extended ion-storage times have proven useful for the investigation of reactions and cluster-decay mechanisms. Collisional and laser excitation have been performed as well as electron-impact ionization for the characterization of cluster properties as a function of the cluster size. More recently, it was realized that the Penning trap set-up is particularly suitable for the production of polyanionic clusters. On the other hand, the clusters themselves are useful probes for the investigation of simultaneously stored charged particles. This paper contains examples of recent experimental results on the production and decay modes of polyanionic clusters, some of which also provide information about the properties of the electron-bath ensemble used in that process.

Trap‐based Cluster Research and Cluster‐based Investigations of Ion Storage at ClusterTrap

ClusterTrap is a setup devoted to the investigation of atomic clusters. The Penning trap allows various studies after preceding preparation steps. In particular, the clusters may be size selected and their charge state may be varied by electron impact ionization or electron attachment during storage. On the other hand the clusters can be used for extended studies of the properties of the Penning trap. Both aspects are described with recent examples.

A Physics Case for SHIPTRAP: Measuring the Masses of Transuranium Elements

SHIPTRAP will allow direct measurement of masses of transuranium nuclides. The method of choice is a Penning trap spectrometer coupled to the SHIP (Separator for Heavy Ion Products) facility at GSI, Darmstadt. In this paper the impact of the SHIPTRAP facility, with its capability of systematic mass measurements with high precision, is explored. Rather few masses of nuclides above uranium are presently known experimentally. In the region of nuclides above Z = 100 no ground state masses were measured directly. SHIPTRAP will play an important role in systematically mapping out this area. Possible candidates for direct mass measurements, even with small or very small production cross sections, are presented.

In-depth study of in-trap high-resolution mass separation by transversal ion ejection from a multi-reflection time-of-flight device

The recently introduced method of ion separation by transversal ejection of unwanted species in electrostatic ion-beam traps and multi-reflection time-of-flight devices has been further studied in detail. As this separation is performed during the ion storage itself, there is no need for additional external devices such as ion gates or traps for either pre- or postselection of the ions of interest. The ejection of unwanted contaminant ions is performed by appropriate pulses of the potentials of deflector electrodes. These segmented ring electrodes are located off-center in the trap, i.e., between one of the two ion mirrors and the central drift tube, which also serves as a potential lift for capturing incoming ions and axially ejecting ions of interest after their selection. The various parameters affecting the selection effectivity and resolving power are illustrated with tin-cluster measurements, where isotopologue ion species provide mass differences down to a single atomic mass unit at ion masses of several hundred. Symmetric deflection voltages of only 10 V were found sufficient for the transversal ejection of ion species with as few as three deflection pulses. The duty cycle, i.e., the pulse duration with respect to the period of ion revolution, has been varied, resulting in resolving powers of up to several tens of thousands for this selection technique.

Unintended Parametric Ejection of Ions from an Ion Cyclotron Resonance Trap by Two-Electrode Axialization

Azimuthal quadrupolar excitation is a commonly used technique in the field of ion cyclotron resonance mass spectrometry, in particular in combination with buffer-gas collisions to achieve axialization of the stored ions. If the quadrupolar excitation is applied with only one phase to a set of two opposing ring segments (rather than the “regular” method where two sets of electrodes are addressed with opposite polarities), parametric resonance effects at the frequencies 2μ z and μp = μ+ – μ– can lead to unintended ejection of ions from the trap. These parametric resonances have been revisited both theoretically and experimentally: multipole components of different azimuthal excitation schemes are derived by a simple vector representation of the excitation signal applied to the ring segments. Thus, parametric contributions can be easily identified, as demonstrated for the two-electrode and the four-electrode quadrupolar excitation schemes as well as further examples. In addition, the effect of the single-phase two-electrode quadrupolar excitation is demonstrated for storage and axialization of cluster ions.

Status of the SHIPTRAP Project: A Capture and Storage Facility for Heavy Radionuclides from SHIP

The ion trap facility SHIPTRAP is being set up to deliver very clean and cool beams of singly-charged recoil ions produced at the SHIP velocity filter at GSI Darmstadt. SHIPTRAP consists of a gas cell for stopping and thermalizing high-energy recoil ions from SHIP, an rf ion guide for extraction of the ions from the gas cell, a linear rf trap for accumulation and bunching of the ions, and a Penning trap for isobaric purification. The progress in testing the rf ion guide is reported. A transmission of about 93(5)% was achieved.

Electron attachment to anionic clusters in ion traps

Ion traps are versatile tools for the investigation of gas-phase cluster ions, allowing, e.g., cluster-size selection and extended reaction times. Taking advantage of their particular storage capability of simultaneous trapping of electrons and clusters, Penning traps have been applied for the production of clusters with high negative charge states. Recently, linear radio-frequency quadrupole traps have been demonstrated to be another candidate to produce polyanionic clusters. Operation with rectangular, rather than harmonic, radio-frequency voltages provides field-free time slots for unhindered electron passage through the trap. Several aspects of electron-attachment techniques by means of Penning and radio-frequency traps are addressed and recent experimental results are presented.