Ingmar Bergström

SMILETRAP : A Penning trap facility for precision mass measurements using highly charged ions

The precision of mass measurements in a Penning trap increases linearly with the charge of the ion. Therefore we have attached a Penning trap, named SMILETRAP, to the electron beam ion source CRYSIS at MSL. CRYSIS is via an isotope separator connected to an ion source that can deliver singly charged ions of practically any element. In CRYSIS charge state breeding occurs by intense electron bombardment. We have shown that it is possible to produce, catch and measure the cyclotron frequencies of ions in the charge region 1 + to 52 +. The relevant observable in mass measurements using a Penning trap is the ratio of the cyclotron frequencies of the ion of interest and ion used as a mass reference. High precision requires that the two frequencies are measured after one another in the shortest possible time. For reasons of convenience the precision trap operates at room temperature. So far it has been believed that warm traps working at 4K are required for high mass precision with exactly one ion in the trap at a time. In this paper we demonstrate that mass precision of a few parts in 10 1 0 also can be obtained in a warm trap at a pressure of about 5 × 10 - 1 2 mbar by stabilizing the pressure in the He-dewar, the trap temperature and the frequency synthesizer. In order to reduce the influence of changes of the magnetic field to a level below 10 1 0 , the scanning of the frequencies close to the resonances of both the ion of interest and the reference ion is done in a total time <2min. Trapping of ions is a statistical procedure, allowing more than one ion to be trapped in each measurement cycle. However, after completing the measurements it is possible to reject all information except for events based on 1 and 2 trapped ions. The procedures of producing, transporting, catching, exciting and measuring the cyclotron resonance frequencies of highly charged ions and the mass reference ions with the time-of-flight method are described. In routine measurements with I s excitation time lasting for about 24 h, atomic masses can be determined at an uncertainty of about 1 pbb. In the case of q/A doublet measurements a mass uncertainty close to 0.1 ppb can be obtained as illustrated by a mass measurement of 4 He 2 + . The mass measurements so far performed are either related to fundamental constants or to masses the accuracy of which is needed for some current questions in physics.

Determination of the 76Ge Double Beta Decay Q Value

The Q value of the (76)Ge double beta decay has been determined by measuring the masses of (76)Ge and (76)Se in a Penning trap using neon- and fluorinelike ions. The obtained masses are 75.921 402 758(96) u and 75.919 213 795(81) u, respectively. The systematic errors of these two determinations are nearly equal, and therefore, the remaining systematic uncertainty of the Q value is drastically reduced. A Q value of 2 039.006(50) keV was obtained improving the accuracy of the accepted value by a factor of 6.

New Mass Value for ^7Li

A high-accuracy mass measurement of 7Li was performed with the SMILETRAP Penning-trap mass spectrometer via a cyclotron frequency comparison of 7Li3+ and H2+. A new atomic-mass value of 7Li has been determined to be 7.016 003 425 6(45) u with a relative uncertainty of 0.63 ppb. It has uncovered a discrepancy as large as 14sigma (1.1 microu) deviation relative to the literature value given in the Atomic-Mass Evaluation AME 2003. The importance of the improved and revised 7Li mass value, for calibration purposes in nuclear-charge radii and atomic-mass measurements of the neutron halos 9Li and 11Li, is discussed.

High-frequency Ramsey excitation in a Penning trap

The Ramsey excitation method for high-precision mass-measurements of highly-charged ions has been investigated and benchmarked using H2+ ions in the Penning-trap mass-spectrometer SMILETRAP. The reason for using H2+ ions are their high cyclotron frequency which is typical for the highly-charged ions usually used at SMILETRAP. Two-, three- and four-pulse Ramsey excitation data are analyzed with the help of recent theoretical work and are compared with the previously used single-pulse excitation data. An improvement factor of 2.9 in the statistical uncertainty is achieved. Furthermore the mass of 76Se, included in the previous Q-value measurement of the 76Ge neutrinoless double beta decay, is checked using 76Se25+ ions and a three-pulse Ramsey excitation. The results show a convincing agreement with the measurement when using single-pulse excitation and therefore our Q-value of 2039.006(50) keV, performed with single-pulse excitation, is confirmed.

Present status of the Stockholm electron beam ion source and its scientific program

The Stockholm electron beam ion source CRYSIS has since 1987 been used for the production of ions with charges in the region 1+ to 60+ for various experiments at low energies as well as for experiments in the storage ring CRYRING. A short summary of these experiments is given. The highly charged ions are produced by electron bombardment of species, either by directly introducing a monoisotopic or almost monoisotopic gas or singly charged isotope separated ions into CRYSIS. The singly charged ions are produced in a plasma ion source, CHORDIS, that can operate with gases, solid material evaporated in an oven or used in a sputtering mode. In this way highly charged ions of practically any element can be produced, even isotopes with a low abundance. The mass selection is done with a 0.5 meter radius doubly focusing magnet that ensures isotopically pure beams even for the heaviest elements. A summary is given of the elements and charge states so far delivered to users.

The Stockholm–Mainz ion trap project

A new ion trap facility is described which is dedicated to studies of highly charged ions in a Penning trap. Such a trap will be connected to sources of highly charged ions, in particular the electron beam ion source CRYSIS, at the Manne Siegbahn Institute for Physics. The use of highly charged ions in a Penning trap increases the cyclotron frequency with a factor proportional to the charge which leads to a higher resolution. Also, the possibility to vary the charge state makes it possible to search for and identify different systematic effects. Thus, a substantial increase in accuracy can be expected. In addition, the combination of high charge state ions and a Penning trap allows new applications where one can take advantage of the controlled measuring situation, long observation time and high resolution detection. The initial priority will be given to high precision mass measurements of heavy stable ions. At a future stage, plans are to extend the use to other applications, such as charge exchange processes between neutrals and stored charged ions, electron impact ionization and exposure of clusters and molecules to highly charged ions as well as lifetime determinations of molecules and clusters.

Chapter 6 Precise Atomic Masses for Fundamental Physics Determined at SMILETRAP

In this paper we describe the features of the SMILETRAP Penning trap mass spectrometer and give examples of recently performed precision mass measurements. SMILETRAP is designed for precision mass ...

The smiletrap (Stockholm-Mainz-Ion-LEvitation-TRAP) facility

Described in this paper is an experimental facility which measures atomic masses by using multiply charged ions from an electron beam ion source. The ions are injected into a Penning trap and the cyclotron frequencies measured. A precision of 2×10−9 has been reached using highly charged carbon, nitrogen, oxygen and neon.

SMILETRAP — Atomic mass measurements with ppb accuracy by using highly charged ions

In the SMILETRAP facility externally produced highly charged ions are captured in a Penning trap and utilized for high precision measurements of atomic masses. Accuracy tests on a ppb level have been performed, using highly charged carbon, oxygen and neon ions. In all cases hydrogen ions served as a reference for the calibration and monitoring of the magnetic field in the trap. Deviations smaller than 3 ppb from the expected results were found in mass measurements of the16O and20Ne atomic masses. The proton atomic mass, determined from the reference measurements on hydrogen ions, is in good agreement with the accepted value [1]. A direct mass measurement on the86Kr-isotope, using trapped86Kr29+-ions is reported.

High-precision mass measurements for fundamental applications using highly-charged ions with SMILETRAP

The Penning trap mass spectrometer SMILETRAP takes advantage of highly-charged ions for high-accuracy mass measurements. In this paper recent mass measurements on Li and Ca ions are presented and their impact on fundamental applications discussed, especially the need for accurate mass values of hydrogen-like and lithium-like ions in the evaluation of the electron g-factor measurements in highly-charged ions is emphasized. Such experiments aim to test bound state quantum electrodynamics. Here the ionic mass is a key ingredient, which can be the limiting factor for the final precision.