Speaker
Description
The FRagment Separator FRS at GSI features three branches for experiments with in-flight separated beams, the symmetric branch, the storage-ring branch connected to the Experimental Storage Ring and CRYRING complex (ESR/CRYRING), and the target hall branch to various caves, where experimental setups for Reaction experiments with Relativistic Radioactive Beams (R3B) and for Biomedical Applications of Radioactive ion Beams (BARB) are located. The symmetric branch is used mainly for spectrometer experiments and implantation experiments, where the nuclei of interest are completely slowed down and thermalized and then studied by decay- or mass-spectrometry. In order to study the most exotic nuclei, the rate of the nuclei of interest is often a critical parameter. For a significant rate increase, a high-transmission ion-optical mode and very thick production targets making use of two-step reactions have been developed and tested; results obtained with Pb and Xe fragment beams will be reported.
At the ESR, an energy-isochronous ion-optical mode has been available for direct mass measurements of very short-lived nuclei for more than two decades. With revolution-time measurements only, the high mass-over-charge accuracy and resolving power is limited to a narrow window in the magnetic rigidity. This statement has been proven first by using slits at the second focal plane of the FRS. Instead of an independent magnetic rigidity measurement, one can also measure the velocity with two TOF detectors as it is foreseen for the CR at FAIR and meanwhile implemented at the CSRe in Lanzhou. An equivalent way is to simultaneously measure the magnetic rigidity and the revolution frequency of each circulating stored ion. Calculations show that an upgraded position sensitive TOF detector, located at a dispersive position in the ESR lattice, will improve the accuracy and the mass resolution without limiting the intensity of the stored exotic nuclei.
The third branch of the FRS leads to the target hall with the medical cave as one possible destination. Recently a joint effort between the FRS and the biophysics groups of GSI was started to perform biomedical experiments relevant for hadron therapy with positron emitting carbon and oxygen beams. The ion-optics and diagnostics for this new branch have been prepared and pure positron emitting $^{15}$O-ions were provided to the medical cave for the first time. An overall conversion efficiency of about $6\times 10^{-4}$ for $^{15}$O fragments per primary $^{16}$O projectile was reached.
Work partly supported by ERC AdG no. 883425 (BARB)
