C. Scheidenberger

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.

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.

Mass Measurements on Short-Lived Nuclides with ISOLTRAP

Penning trap mass spectrometry has reached a state that allows its application to very short-lived nuclides available from various sources of radioactive beams. Mass values with outstanding accuracy are achieved even far from stability. This paper illustrates the state of the art by summarizing the status of the ISOLTRAP experiment at ISOLDE/CERN. Furthermore, results of mass measurements on unstable rare earth isotopes will be given.

Vavilov-Cherenkov radiation emitted by heavy ions near the threshold

Abstract The Vavilov–Cherenkov radiation (VChR) emitted by the heavy ions 79 Au was studied by the photography method. The photographs of the radiation near and below the VChR threshold are published for the first time.

A linear radiofrequency quadrupole ion trap for the cooling and bunching of radioactive ion beams

Abstract A linear radio-frequency quadrupole ion guide and beam buncher has been installed at the ISOLTRAP mass spectrometry experiment at the ISOLDE facility at CERN. The apparatus is being used as a beam cooling, accumulation, and bunching system. It operates with a buffer gas that cools the injected ions and converts the quasicontinuous 60-keV beam from the ISOLDE facility to 2.5-keV beam pulses with improved normalized transverse emittance. Recent measurements suggest a capture efficiency of the ion guide of up to 40% and a cooling and bunching efficiency of at least 12% which is expected to still be increased. The improved ISOLTRAP setup has so far been used very successfully in three on-line experiments.

Isochronous Mass Measurements of Hot Exotic Nuclei

A novel method for mass measurements of short-lived exotic nuclides is presented. Exotic nuclides were produced and separated in flight at relativistic energies with the fragment separator (FRS) and were injected into the experimental storage ring (ESR). Operating the ESR in the isochronous mode we performed mass measurements of neutron deficient fragments of 84Kr with half-lives larger than 50 ms. However, this experimental technique is applicable in a half-life range down to a few μs. A mass resolving power of 110000 (FWHM) has been achieved. Results are presented for the masses of 68As, 70,71Se and 73Br.

Spectroscopy of η′-nucleus bound states at GSI and FAIR --very preliminary results and future prospects--

The possible existence of η′-nucleus bound states has been put forward through theoretical and experimental studies. It is strongly related to the η′ mass at finite density, which is expected to be reduced because of the interplay between the UA(1) anomaly and partial restoration of chiral symmetry. The investigation of the C(p,d) reaction at GSI and FAIR, as well as an overview of the experimental program at GSI and future plans at FAIR are discussed.

Mass Measurements of Stored Exotic Nuclei at Relativistic Energies

Relativistic exotic nuclei produced via projectile fragmentation were separated in flight by the fragment separator FRS and injected into the storage ring ESR for precise mass measurements using Schottky spectrometry. Nuclei with half-lives shorter than the time required for electron cooling have been investigated by time-of-flight measurements with the ESR being operated in the isochronous mode. This novel experimental technique gives access to all nuclei with half-lives down to the μs-range.

Carbon cluster ions for a study of the accuracy of ISOLTRAP

Cyclotron frequency measurements of singly charged carbon clusters 12C+n were carried out with the ISOLTRAP apparatus. The carbon cluster ions were produced externally by use of laser-induced desorption, fragmentation, and ionization of C60 fullerenes. They were injected into and stored in the Penning trap system. The observation of carbon clusters of different sizes has provided detailed insight into the final mass uncertainty achievable with ISOLTRAP and yielded a value of u(m)/m=8⋅10−9. Since the unified atomic mass unit is defined as 1/12 the mass of the 12C atom, ISOLTRAP can now be used to carry out absolute mass measurements.

Schottky Mass Measurements of Cooled Exotic Nuclei

Projectile fragments of a 209Bi beam were separated in flight with the fragment separator FRS and injected into the experimental storage ring ESR. In the ESR a beam containing up to about 100 different isotopes was cooled to a relative velocity spread of δυ/υ = 10 by means of the electron cooler. The image currents of the ions induced in a Schottky pick-up probe at each turn were recorded. A subsequent Fast Fourier Transformation of these signals yields the revolution frequencies of the different isotopes stored in the ESR. Unknown masses of more than 150 neutron-deficient nuclides in the element range of 52 ≤ Z ≤ 85 have been measured directly by Schottky Mass Spectrometry and in addition more than 60 new masses have been obtained from α-decay chains. These new mass data allow the location of the one-proton dripline and the prediction of the two-proton dripline for heavy nuclides. The experimental masses are compared with different theoretical predictions.