Abstract
At radioactive ion beam facilities like ISOLDE at CERN, a high purity of the element of interest in the ion beam is essential for most experiments on exotic nuclei. Due to its unique combination of high ionization efficiency and ultimate elemental selectivity, the Resonance Ionization Laser Ion Source, RILIS, has become the most frequently used ion source at ISOLDE and at the majority of similar facilities worldwide. However, isobaric contamination predominantly stemming from unspecific surface ionization may still introduce severe limitations. By applying the highly selective resonance ionization technique inside a radio-frequency quadrupole ion guide structure, the novel approach of the Laser Ion Source and Trap, LIST, suppresses surface ionized isobaric contaminants by an electrostatic repelling potential. Following extensive feasibility studies and off-line tests, the LIST device has been adapted and refined to match the stringent operational constraints and to survive the hostile environment of the ISOLDE front-end region enclosing the highly radioactive nuclear reaction target. The LIST operation was successfully demonstrated for the first time on-line at ISOLDE during two experiments, attesting its suitability for radioactive isotope production under routine conditions. Data of these on-line characterization measurements confirm a suppression of surface-ionized isobars by more than a factor of 1000 in accordance to off-line studies that were carried out for the preparation of the on-line experiments. During the first on-line test, the suppression was associated with an efficiency loss of not more than a factor of about 50 with respect to normal RILIS operation. These losses could be further reduced to only about 20 during the second run. Results of the off-line studies in comparison to the first on-line characterization data are discussed here.
Highlights
The artificial production of short-lived exotic nuclei far off stability enables unique possibilities for the investigation of phenom-⇑ Corresponding author at: CERN, 1211 Geneva 23, Switzerland.ena in various fields of fundamental as well as applied physics
In this paper we report on the characterization and the implementation of the Laser Ion Source and Trap (LIST) into ISOLDE, as well as on the results of the first on-line test of a LIST device coupled to a thick-target hot-cavity ion source assembly
It is expected that laser ionization inside the hot-cavity contributes to the loss factor since a small fraction of atoms corresponding to the RILIS laser ionization efficiency is already laser ionized inside the hot cavity before reaching the radio-frequency quadrupole (RFQ) and are repelled by the repeller voltage together with the contaminants
Summary
The artificial production of short-lived exotic nuclei far off stability enables unique possibilities for the investigation of phenom-⇑ Corresponding author at: CERN, 1211 Geneva 23, Switzerland.ena in various fields of fundamental as well as applied physics. The artificial production of short-lived exotic nuclei far off stability enables unique possibilities for the investigation of phenom-. The development of nuclear masses and ground state properties along the nuclear chart [1] are of fundamental relevance for astrophysics [2], and in particular nucleosynthesis [3], while nuclear decay properties map the stability of nuclear matter and pave the way to new physics beyond the standard model [4]; short-lived isotopes serve as ideal probes for studies on the behavior and defects in solid state physics [5] or as biomedical markers [6].
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