163Ho Distillation and Implantation for HOLMES Experiment

Description

HOLMES is an experiment to directly measure the neutrino mass with a calorimetric approach. The calorimetric technique eliminates several systematic uncertainties usually present in spectrometers where the external source and decays to excited states affect the measurement. 163Ho is chosen as source for its very low Q value (2.8 keV), the proximity of the end-point to resonance M1 and its half life (4570 year). These features are optimal to reach simultaneously a reasonable activity to have sufficient statistics in the end-point and a small quantity of 163Ho embedded in the detector not to alter significantly its heat capacity. 163Ho will be produced via neutron irradiation of enriched 162Er2O3 at the Institute Laue–Langevin (Grenoble, France), and chemically separated at Paul Scherrer Institut (Villigen, Switzerland). It will arrive at INFN laboratory of Genova in oxide form (Ho2O3) with traces of others Ho isotopes and contaminants not removable using chemical methods. In particular, the metastable 166mHo undergoes beta decay with a half life of about 1200 year, if present 166mHo induces background below 5 keV. The removal of these contaminants is critical for HOLMES so a dedicated system is being set up. The system is designed to achieve an optimal mass separation for 163Ho and consists of two main components: an evaporation chamber and an ion implanter. In the evaporation chamber, holmium will be reduced in metallic form, using the reaction 2Y+Ho2O3 → Y2O3+2Ho and used to produce a metallic target for the ion implanter source. The ion implanter consists of five main components: a Penning sputter ion source, an acceleration section, a magnetic/electrostatic mass analyser, a magnetic scanning stage and a focusing electrostatic triplet. In this contribution, we describe the procedures, under continuous refinement, for the holmium evaporation process, the ion-implanted metallic target production and the status of the ion implanter.

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