  For the research of CCD neutron radiography, a neutron collimator was
designed based on the exit of thermal neutron of the Boron Neutron Capture
Therapy (BNCT) reactor. Based on the Geant4 simulations, the preliminary choice
of the size of the collimator was determined. The materials were selected
according to the literature data. Then, a collimator was constructed and tested
on site. The results of experiment and simulation show that the thermal neutron
flux at the end of theneutron collimator is greater than 10^6 n/cm^2/s, the
maximum collimation ratio (L/D) is 58, the Cd-ratio(Mn) is 160 and the diameter
of collimator end is 10 cm. This neutron collimator is considered to be
applicable for neutron radiography.
