Abstract
The applications of radiation have been quite extensive recently. Such as medical check-ups,therapies, the food industry and even more complicated technological applications can justify the contributions to human civilization which was brought by radiation. The paper observes the bidirectional property which is vertical and horizontal in the metal pipe by neutron radiography. National Tsing Hua University is equipped with stable and high quality thermal neutron(THOR) which can support the need of neutron radiography in this experiment. Neutron radiography utilizes the attribution of the interaction between neutrons and other materials. Compared to X-ray,almost neutrons interact cross section with metal is low than X-ray;therefore, they can easily pass through the metal pipe. Neutrons, however, easily interact with water and the are blocked by water. The paper calculates the void fraction by observing the bidirectional property in the metal pipe that results from the different interactions between different neutrons and materials. Since the imaging Properties is very suitable to estimate and analyze void fraction、bubble rising velocity. That is, the paper put emphasis on neutron radiography and the comparison of void fraction