The crystal spectrometer combined with the CCD detectors serves to measure angles
with optimized resolution and luminosity. It is planned to use a very similar
arrangement as in a recent test measurement where the pionic deuterium
transition has been measured at a pressure of 2.5 bar. This measurement serves
as a basis for the discussion of this proposal in terms of resolution and rates.
The corresponding spectrum obtained with a Si (111) crystal is shown in Fig.
6.
The rate of measured deuterium X-rays is 
for a
continuously running machine at 1.5 mA. The peak/background ratio is 
.
This result shows a substantial improvement compared to a recent measurement
of pionic deuterium X-rays at PSI [69]. For the proposed experiment
crystals will be preferentially used as will be explained below.
These crystals have a factor of 2 -5 lower reflectivities. With vertically bigger
CCD detectors and an improved stop efficiency this loss will be overcompensated.
The excellent peak/background ratio can be improved further by carefully tailoring
a shielding around the path of the X-rays thus reducing the background and
by enhancing the stop rate in hydrogen. An improvement factor of about three
can safely be expected. Before going into more technical details the gross features
of crystal spectroscopy together with some basic relations are introduced.
111
spherically bent crystal.