Measuring small samples at the ISIS muon source

Studying samples appreciably smaller than the muon beam spot size, using conventional masked holders, is complicated by the detection of positrons from the muons stopped in the masking material. A technique of suspending samples in the beam as a method of overcoming these inherent difficulties has been developed; muons not implanted in the sample are now able to fly-past and their contribution is removed from the measured signal. The implementation of this method on the EMU spectrometer at ISIS is described in this paper. Details of modifications to equipment to enable this type of operation and the results obtained from several test experiments are reported. Practical details associated with carrying out experiments using suspended samples are also considered. Although greatly reduced, background counts are still present in the data; experiments investigating the source of these counts and future improvements to the apparatus are considered.