CERN-ISOLDE. Laser ionization and direct in-source spectroscopy of refractory and negatively charged radioisotopes at ISOLDE and the laser ion sources RILIS and LIST. Final report

The expansion of the accessible element and isotope spectrum, the continuous optimization of the purity of the ion beams and the provision of direct and now high-resolution laser spectroscopy within the ion source were successfully demonstrated and made available for ISOLDE's standard portfolio. As an additional point, the production of negatively charged ions at ISOLDE was resumed and optimized in the last three funding periods so that the physically relevant determination of electron affinity could be carried out using laser photodetachment spectroscopy. The individual work packages of the application were handled as follows: WP1: Expansion of the element spectrum of the 'hot-cavity' ion source. The phase of the Long Shutdown 2 at CERN from December 10, 2018 - March 31, 2021 was used to revise important ion source components, especially the radio frequency supply for the LIST and the adaptation to the new front ends at ISOLDE. The demonstration of high-resolution in-source spectroscopy and its use for studying long-lived radionuclides took place offline at RISIKO in Mainz during this time. At CERN, high-resolution investigations using two-photon spectroscopy were completed and published, new elements were discovered at ISOLDE and for CERN-MEDICIS, and the new time-of-flight ion source concept was used to carry out experiments using high voltage gradients in the ion source cavity. The time compression of the ion bunch structure, which is imposed by the laser pulse, increases selectivity in conjunction with the downstream beam gating technique. WP2: Implementation of high-resolution in-source laser spectroscopy. At RISIKO, the LIST ion source in Mainz was used for high-resolution nuclear structure measurements on radioisotopes of technetium, promethium and the artificially produced actinides americium, curium and californium. Experimental line widths of down to 60 MHz were demonstrated, comparable to the complex collinear apparatuses Collaps and CRIS. The core of the system is a powerful, pulsed and narrow-band laser system that uses a titanium:sapphire cw master laser built in collaboration with Nagoya University. This is a cost-effective alternative to commercial systems and is to be introduced in several areas of high-resolution laser spectroscopy at ISOLDE in the near future. This will enable the potential of direct laser spectroscopy within the LIST structure to be further advanced for both offline and online use. WP3: Measurements on and provision of high-purity negative ion beams via photodetachment. In the area of negative ions, a highlight was already achieved at the beginning of the reporting period with the first-time determination of the electron affinity of astatine. This was made possible, among other things, by preliminary work in the previous project in the area of the ion source and the development of the measuring equipment. To expand the possibilities, the infrastructure of the GANDALPH measuring equipment was expanded with a new neutral particle detector and a quadrupole mass filter. In cooperation with the MIRACLS collaboration at CERN, the concept of laser spectroscopy on negative ions was expanded to include multi-reflection ToF systems. A coupling to the CRIS experiment and the measurement of the electron affinity of polonium are in preparation.