Highly efficient isotope separation and ion implantation of ${}^{163}$Ho for the ECHo project

Abstract

The effective electron neutrino mass measurement at the ECHo experiment requires high purity ${}^{163}$Ho, 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 ${}^{163}$Ho was optimized. A new two-step resonant laser ionization scheme was established at the $30kV$ magnetic mass separator RISIKO. This achieved ionization and separation efficiencies with an average of $69(5{)}_{\text{stat}}(4{)}_{\text{sys}}\%$ using intra-cavity frequency doubled Ti:sapphire lasers. The implantation of a ${}^{166\text{m}}$Ho impurity is suppressed 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 $20(2)\%$.