Two three-dimensional neutron streaming problems are analyzed by using the Monte Carlo coupling technique. One is streaming through a two-legged cylindrical-annular duct and the other is streaming through a slit. The main advantage of breaking the problem into two Monte Carlo calculations is that it is then not necessary to repeat the calculation of neutron transport from the reactor to the pseudo-detector when the duct or the slit configuration is changed. The coupling technique provides a remarkable improvement in both the calculated results and the fractional standard deviations as compared with usual Monte Carlo calculations. The agreement between the measured reaction rates and the calculated values is quite satisfactory. The calculated values using the coupling technique agree with the measured values within a factor of 2 for In(n,n′) and Ni(n,p) threshold detectors in the two-legged cylindrical-annular-duct problem, and agree within a factor of 3 with results from cadmium-covered gold activation detectors and from In(n,n′), Ni(n,p), and S(n,p) threshold detectors in the slit problem. However, there is a relatively large discrepancy between the calculated and the measured values from the cadmium-covered gold activation detector in the cylindrical-annular-duct problem.
