The Trigger Detector
In order to perform µSR-experiments with low-energy muons
a proper time-zero signal is needed to start the 'clock' of
the µSR-measurement. At a pulsed muon beam facility the pulse of
the accelerator itself can be used as a start signal. This is
no longer possible at the dc-muon beams available at PSI.
For the low-energy muons the beam counter signal also can not be used
due to its too high rate of up to 14 Mcps.
In our
present experimental setup we obtain this time information from a
secondary electron detector - the so-called trigger detector,
which detects keV muons when passing an ultrathin carbon foil
(2.2 µg/cm2 ).
The muons traversing the foil emit a few electrons, which are deflected by
90 degrees and detected by a MCP to give the start signal for
the µSR-measurement. The energy loss of the muons in the foil amounts to
1.6 keV with a gaussian energy straggling (sigma = 500 eV).
The detection efficiency for keV muons is measured to ~80%.
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