R.B. Moore

The accuracy of heavy‐ion mass measurements using time of flight‐ion cyclotron resonance in a Penning trap

Ion motion in a Penning trap and the electrical signals it can produce have been analyzed for the purpose of identifying the important causes of uncertainty in high‐accuracy mass measurements of heavy ions. The role of the azimuthal quadrupole electric field in signal pickup, and its effects on ion motion at the sum frequency of the cyclotron and magnetron motions, have been identified. A useful scheme for calculating the signal strength and strength of the interaction between an applied field and the ion motion has been developed. The important sources of uncertainty in using the sum frequency of the cyclotron and magnetron motions for determining the ion mass are discussed. Particular application is made to the case of cyclotron resonance detection by observation of the time of flight of ejected ions.

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.

ISOLTRAP: a tandem Penning trap system for accurate on-line mass determination of short-lived isotopes

The tandem Penning trap mass spectrometer ISOLTRAP has been set up at the on-line mass separator ISOLDE at CERN/Geneva for accurate mass measurements of short-lived nuclei with T12 ≥ 1 s. The mass measurement is performed via the determination of the cyclotron frequency of an ion in a magnetic field. The design of the spectrometer matches the particular requirements for on-line mass measurements on short-lived isotopes. With the ISOLTRAP spectrometer masses of more than 70 radioactive nuclei have so far been determined with resolving powers exceeding one million and an accuracy of typically 10−7.

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.

First absolute mass measurements of short-lived isotopes

Absolute mass measurements of short-lived isotopes have been performed at the on-line mass separator ISOLDE at CERN by determining the cyclotron frequencies of ions confined in a Penning trap. The cyclotron frequencies for77,78,85,86,88Rb and88Sr ions could be determined with a resolving power of 3×105 and an accuracy of better than 10−6, which corresponds to 100 keV for massA=100. The shortest-lived isotope under investigation was77Rb with a half-life of 3.7 min. The resonances obtained for the isobars88Rb and88Sr were clearly resolved.

High-accuracy mass determination of unstable cesium and barium isotopes

Abstract Direct mass measurements of short-lived Cs and Ba isotopes have been performed with the tandem Penning trap mass spectrometer ISOLTRAP installed at the on-line isotope separator ISOLDE at CERN. Typically, a mass resolving power of 600 000 and an accuracy of δm ≈ 13 keV have been obtained. The masses of 123,124,126 Ba and 122 m Cs were measured for the first time. A least-squares adjustment has been performed and the experimental masses are compared with theoretical ones, particularly in the frame of a macroscopic-microscopic model.

Penning trap mass measurements of neutron deficient Rb and Sr isotopes

Abstract The Penning-trap mass spectrometer ISOLTRAP installed at the on-line mass separator ISOLDE 2 at CERN has been used for mass determination of 75–87 Rb and 78–83,87 Sr. Ions are captured in a Penning trap and their cyclotron frequency ω c = ( q m )B in the trapping field B is measured. Ratios of these frequencies lead to the determination of the atomic mass of these isotopes. A resolving power of typically m Δm = 10 6 and an accuracy of δm ≈10 keV is obtained. The mass of 78 Sr is measured for the first time and, in most cases, the mass values of the other isotopes are significantly improved. The experimental masses are compared with theoretical predictions.

Mass determination of francium and radium isotopes by a penning trap mass spectrometer

Abstract A tandem Penning trap mass spectrometer is used for mass measurement of radioactive isotopes produced at the on-line isotope separator ISOLDE/CERN. The mass is determined directly and with high accuracy by measuring the cyclotron frequency of the stored ions. Measurements were performed on 209 210 211 212 221 222Fr and 226 230Ra. A resolving power of 5 × 105 was used and an accuracy of 1·8 × 10−7 has been achieved.

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.

In-flight Capture of an Ion Beam in a Paul Trap

Abstract A system for collecting 60 keV ion beams was set up at the ISOLDE-3 radionuclide mass-separator facility at CERN. Electric field retardation was used to bring the ions to 20 eV for injection into a Paul trap. Tests were made with 132Xe+ and 79Br− ions. A trap potential well depth of about 30 V could be created. At this well depth a collection efficiency of about 0·2% was obtained for a xenon beam of emittance about 2π mm-mrad and energy spread estimated to be of a few electronvolts. The efficiency for bromine ions was less, but still appreciable. The efficiencies achieved indicate that a sizeable fraction of the ions arriving at the correct rf window for acceptance by the trap were being collected. To the limit of the apparatus, the efficiency was increasing in proportion to the third power of the rf amplitude applied to the trap, indicating that it was proportional to the phase space volume of the trap. These results are now being used to design a larger Paul trap collection system for installat...