Research On Optimization Of Target Film Material For Sealed Neutron Tube

The neutron tube is a kind of small accelerator neutron source which is composed of ion source,target,acceleration system and air pressure regulating system.It is widely used in many fields,such as nuclear physics,neutron logging,neutron photography,explosives detection,cancer treatment and so on.Neutron yield is one of the main parameters of neutron tube.Increasing neutron tube yield can meet the requirements of more research fields.The target is one of the main components of neutron tube.There are two kinds of sealed neutron tube:commercial target neutron tube and drive-in target neutron tube.The target film not only stores deuterium(tritium)atoms,but also is the interface of nuclear reaction.The yield and lifetime of neutron tube are affected by the fabrication process,material and thickness of target film.The titanium is widely used as target film material for neutron tube because of its good hydrogen absorption performance,but its defects will affect the life and output of neutron tube.In the working process of neutron tube,the ion beam will be accompanied by impurity ions such as C~+,N~+,O~+when it flows through the ion source.Impurity ions reduce the adsorption probability of hydrogen on the surface of the target film,affect the distribution of ions in the target film,and easily cause target damage.The hydrogen embrittlement of pure titanium target film can be effectively improved by titanium target alloying,and the sputtering resistance of target film can be improved.The appropriate thickness of the protective layer on the surface of the alloy target film can not only prevent the oxidation of the target film,but also reduce the energy loss of the incident ions and improve the neutron yield of the neutron tube.In this article,pure titanium target films were prepared on alumina substrate by magnetron sputtering.The neutron yields of pure titanium target D-D neutron tube and drive-in target neutron tube were measured by using the neutron monitoring system in the laboratory.The measured results are in good agreement with the simulated values.The target neutron yield and sputtering yield of three kinds of alloy target(Scandium-titanium,Molybdenum-titanium,Niobium-titanium)neutron tubes with different ratios are calculated.The results show that the neutron yield increases with the increase of incident beam energy,and the sputtering yield of 0.4 scandium-titanium alloy is relatively low.The neutron yields of neutron tubes with different doping ratios(0.2,0.4,0.6,0.8,1.0)and 7.5 nm Pd protective layer were calculated.According to the calculation results,scandium-titanium alloy with the ratio of 0.4 is an ideal target film material for neutron tube.And the target material can be further optimized and the neutron yield can be increased by plating 7.5 nm Pd protective layer.The neutron yields of three neutron sources(Penning,Microwave and RF)were calculated.The neutron yield of Penning ion source was significantly lower than that of the other two because of the different proton ratios due to different ion sources.In the experimental operation of neutron tube,although the actual measured value of neutron yield is lower than the theoretical value,the optimization of target film material can effectively improve the neutron yield of neutron tube.