Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The Electron Capture in ¹⁶³Ho experiment (ECHo) aims at measuring the mass of the electron neutrino by analysing the EC spectrum of the long-lived radionuclide ¹⁶³Ho (T_1/2 = 4570 a) with a metallic magnetic calorimeter (MMC). For the determination of a reasonable upper limit for the neutrino mass it is mandatory to keep the contamination with the long-lived radionuclide ¹⁶⁶mHo (T_1/2 = 1132.6 a) nine orders of magnitude below the ¹⁶³Ho content. The ion-implantation of ultra-pure ¹⁶³Ho into a MMC for the experiment is carried out by the RISIKO (Resonance Ionization Spectroscopy in KOllinear geometry) mass separator. The separation from ¹⁶⁶mHo, however, cannot be guaranteed to such low levels as needed in this project, it can only be estimated. Here we present our approach to determine the corresponding low isotopic ratio with accelerator mass spectrometry (AMS). Of course, this requires the formation of negative ions, where we find the highest negative ion yield for the anion HoO₂−. For first tests, stable ¹⁶⁵Ho was implanted by RISIKO into various different metal foils and we studied the overall Ho detection efficiency for our setup. We will present first results and estimates of the expected detection limit for the ¹⁶⁶mHo/¹⁶³Ho isotope ratio.