Ultracold Neutron Detection With Li-6-Doped Glass Scintillators Nanosc: A Fast Ultracold Neutron Detector For The Nedm Experiment At The Paul Scherrer Institute

This paper summarizes the results from measurements aiming to characterize ultracold neutron detection with Li-6-doped glass scintillators. Single GS10 or GS20 scintillators, with a thickness of 100-200 mu m, fulfill the ultracold neutron detection requirements with an acceptable neutron-gamma discrimination. This discrimination is clearly improved with a stack of two scintillators: a Li-6-depleted glass bonded to a Li-6-enriched glass. The technique of optical contact bonding is used between the two glasses in order to eliminate the need for optical glue or grease between them. Relative to a 3 He Strelkov gas detector, the scintillator's detection efficiency is lower for UCN energies close to the scintillator's Fermi potential (85-100 neV), but becomes larger at higher UCN energies. Coupled to a digital data acquisition system, counting rates up to a few 10(5) counts/s can be handled. A detector based on such a scintillator stack arrangement was built and has been used in the neutron electric dipole moment experiment at the Paul Scherrer Institute since 2010. Its response for routine runs of the neutron electric dipole moment experiment is presented.