Neutron streaming through conical ducts in a water shield

Abstract

The effect of the tapering angle on the decrease in the thermal-neutron flux density along conical ducts was determined experimentally, as well as by means of Monte Carlo calculations. The ducts were surrounded by the water shield alongside an ORR-type reactor. The experiment was repeated with different parts of the ducts lined with cadmium, so as to measure different streaming components separately. With the sidewalls of the ducts lined, the direct components were measured and with the front entrances lined, the leaking components were measured. Values for the reflection components were obtained by subtracting the sum of these two components from the measured total flux densities. The experimental and calculated results agree, for all components, within the errors involved. Whereas the tapering angle has no effect on the direct components, the other components show a more rapid decrease along the duct axis with increasing tapering angles. However, this effect seems not to be attributable to changes in the differential reflection properties of the duct walls, but is rather a direct effect of the tapering angle on the distancesbetween consecutive reflections from the walls.