Neutron radiography with compact accelerator at Peking University: Problems and solutions

The better contrast sensitivity and resolution of neutron radiographs require higher neutron flux and enough L/D. The neutron yield of compact accelerator-driven neutron sources is usually lower than reactor and spallation neutron sources. It is difficult to obtain the high L/D and the high neutron flux simultaneously. The deuteron beam and Be target were selected for Peking University neutron imaging facility (PKUNIFTY), which can give higher neutron yield at lower beam energy. That means smaller facility size and lower power consumption in the accelerator, and therefore the lower cost. But that reaction also gives higher yield, so how to realize higher n/ratio is another issue. For intense deuteron beam the deuterons lost in the structure materials may become target atoms and generate neutrons under the bombardment of the succeeded beam. This paper will discuss the above problems, and introduce the PKUNIFTY design, which tried to reach a compromise among the various conflicting demands and meet the basic requirements of neutron radiography.