  The work presented in this thesis forms part of a program at the Paul
Scherrer Institute (PSI) to construct a high intensity superthermal ultra-cold
neutron (UCN) source based on solid deuterium as UCN production medium. We
carried out a set of experiments to gain a better understanding of the
properties and the behaviour of solid deuterium as a cold neutron moderator and
ultra-cold neutron converter.
  We present the measurements of the total neutron cross section as obtained by
transmission studies with very cold neutrons and ultra-cold neutrons in solid
deuterium. The experimental set-up and the methods of data analysis are
described and also the procedure of preparing the solid deuterium samples is
given. The neutron transmission studies are supported by optical investigation
of the crystal and by Raman spectroscopy. We have thus characterised the
temperature dependence of the neutron transmission through solid deuterium and
we have been able to identify the role that coherent neutron scattering plays
for the investigated deuterium samples.
