A COMPARISON OF EXPERIMENT AND SIMULATION FOR NEUTRON GUIDANCE THROUGH GLASS POLYCAPILLARY FIBERS

The transmission efficiency and exit divergence of cold neutrons guide d through straight and bent polycapillary fibers made of borosilicate glass have been measured. Experimental results have been compared with a ray-tracing simulation. Good agreement between the two has been obt ained by considering in the simulation only reflectivity losses due to absorption. Therefore, we conclude that the influence of other loss m echanisms on reflectivity, such as surface roughness and waviness, are not significant compared with absorption loss for the borosilicate po lycapillary fibers we have measured. Using the same simulation program , we have characterized the performance of a neutron focusing lens pla ced at the end of a Ni-58 guide tube and optimized for a neutron spect rum from a cold source at a temperature of 65 K. An order of magnitude increase in neutron intensity within a submillimeter focal spot is pr edicted.