Muon spin spectroscopy (μSR) is an experimental technique which utilizes the muon as a fully polarized spin probe to study the properties of condensed matter. The operation of a μSR spectrometer is based on the detection of muons entering the sample and the corresponding decay positrons. For this purpose traditionally scintillation detectors based on photomultiplier tubes (PMTs) are used.
Multipixel Geiger-mode Avalanche Photodiodes (G-APDs) are recently developed solid state photodetectors competitive to PMTs in terms of gain and photon detection efficiency, but insensitive to magnetic fields. They are most suited for compact, finely segmented detectors intended for operation in the presence of high magnetic fields.
In this work we demonstrate the potential of G-APD based detectors for the development of the μSR technique. For the 5 T Avoided Level Crossing instrument located at the Swiss Muon Source of the Paul Scherrer Institut (PSI, Villigen, Switzerland) we are building a completely new detector system using as a basic element a tile-fiber scintillation counter with a G-APD readout. For the planned 10 T high magnetic field spectrometer we are carrying out feasibility tests aiming at the highest possible time resolution. A counter constructed as a G-APD directly coupled to a fast plastic scintillator was tested at detection of minimum ionizing electrons from a ⁹⁰Sr source. With about 0.33 MeV deposited energy the time resolution of σ = 35 ps has been measured.