  A novel radiation detector based on an artificial single crystal diamond was
used to characterize in detail the energy distribution of neutron reference
fields at the Physikalisch-Technische Bundesanstalt (PTB) and their
contamination with charged particles. The monoenergetic reference fields at PTB
in the neutron energy range from 1.5 MeV up to 19 MeV are generated by proton
and deuteron beams impinging on solid and gas targets of tritium and deuterium.
The energy of the incoming particles and the variation of the angle under which
the measurement is performed produce monoenergetic reference fields with
different mean energies and line shapes.
  In this paper we present high resolution neutron spectrometry measurements of
different monoenergetic reference fields. The results are compared with
calculated spectra taking into account the actual target parameters. Line
structures in the order of 80 keV for a neutron energy of 9 MeV were resolved.
The shift of the mean energy and the increasing of the width of the neutron
peak with increasing pressure in the gas target in the order of 30 keV were
measured.
  Another result is the determination of the contamination of the neutron field
at 14 MeV with high energy charged particles (protons) from side reactions
inside the T-target.
  The experiments have shown that this detector is an easy to operate compact
neutron spectrometer with extremely good energy resolution and that detailed
structures in the line shapes of monoenergetic neutron fields can be resolved
without using time of flight techniques.
