The ISOLDE resonance ionization laser ion source (RILIS) allows to ionize efficiently and selectively many metallic elements. In recent yield surveys and online experiments with the ISOLDE RILIS we observed 23 (Submitted to Nuclear Instruments and Methods in Physics Research B)
IntroductionThe resonance ionization laser ion source (RILIS) [1] provides an efficient, fast and selective way to ionize many metallic elements. The elements ionized with the ISOLDE RILIS were reviewed recently [2,3,4]. In this article we will discuss on-line results, i.e. release curves and yields measured in recent target tests, nuclear spectroscopy experiments and on-line collections.The measured release curves were fitted with the empiric 4-parameter-formula described in [5,6]. Table 1 shows a summary of the release parameters: t r the rise time, t f the fall time of the fast component, t s the fall time of the slow component and α the relative intensity of the fast component. Parameters which had to be fixed to obtain a stable fit are marked in parentheses.The release parameters were used to determine for each radio-isotope the fraction which is released before it decays. The on-line efficiency of the RILIS cannot be easily monitored as in the case of a plasma ion source where the support gas is injected at a well-defined flowrate. Still a rough estimate can be made by scaling the off-line measured efficiency with the laser power available in the on-line run. Also the ion yield of a longlived isotope with known production cross-section gives an indication of the ionization efficiency. Correcting the ion yields for the released fraction and the ionization efficiency allows to deduce the in-target production yield. In some of the following graphs both values are plotted: the ion yield, showing the presently available radioactive ion beam intensity for the user, and the in-target production yield showing the theoretical limit that could be obtained with an ideal target (no decay losses) of the same thickness and dimensions coupled to an ideal ion source (100 % efficiency). The ratio between both curves shows the overall efficiency of the present target and ion source unit.
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