Status of the Ho-163 Source Preparation, Purification and Characterization for the ECHo Neutrino Mass Measurement

The ECHo collaboration addresses the determination of the electron neutrino mass by recording the spectrum following electron capture of Ho-163. After production from enriched Er-162 in the ILL high flux nuclear reactor the Ho-163 is separated and purified before implantation into the tiny 0.18 mm4/times$0.18 mm Au-absorbers of the metallic magnetic calorimeters of the ECHo detector array. Highly efficient laser resonance ionization and high transmission mass spectrometric selection is carried out at the 30 kV RISIKO magnetic sector field mass separator. This step ensures elemental and isotopic selectivity for ultra-pure Ho-163 ion implantation with sub-millimeter beam spot size and minimum losses of the precious radioisotopic material. In-situ deposition of Au onto the implantation area of the absorbers using pulsed laser deposition is performed in parallel with the ion implantation, ensuring homogeneous Ho-163/Au-layer formation and reducing disturbing erosion from the sputtering process during implantation. The purity of the ECHo source material during the whole preparation process is monitored by a variety of analytical techniques, including gamma spectrometry, neutron activation, and different mass spectrometric approaches, i.e. ICP-MS, AMS and RIMS. Specifications achieved are discussed in comparison to the needs for the ECHo experiment.