Highly efficient isotope separation and ion implantation of 163Ho for the ECHo project

The effective electron neutrino mass measurement in the framework of the ECHo experiment requires radiochemically pure Ho-163, which is ion implanted into detector absorbers. To meet the project specifications in efficiency and purity, the entire process chain of ionization, isotope separation, and implantation of Ho-163 was optimized. A new two-step resonant laser ionization scheme was established at the 30 kV magnetic mass separator RISIKO. For ionization and separation, an average efficiency of 69(5)(stat)(4)(sys) % was achieved using intra-cavity frequency doubled Ti:sapphire lasers. The implantation of undesired Ho-166m, which is present in trace amounts in the initial Ho-163 sample is suppressed by about five orders of magnitude by the mass separation. A dedicated implantation stage with focusing and scanning capability enhances the geometric implantation efficiency into the ECHo detectors to 20(2) %.