@misc{oai:repo.qst.go.jp:00064730,
 author = {Kamada, So and Takada, Masashi and Suda, Mitsuru and Hamano, Tsuyoshi and et.al and 鎌田 創 and 高田 真志 and 須田 充 and 濱野 毅},
 month = {Sep},
 note = {Lithium is a useful material as a low energy neutron production target, because production yields from p-Li reaction is high, and energy spectrum is soft and shows monochromatic peak. Mono-energetic neutrons are suitable for the calibrations of dosimeters, the testing of semiconductor devices for single-event upset, the neutron biological effect researches, and so on, which are required the neutron energy dependencies. The p-Li reaction is ideal as a neutron source for the accelerator Boron Neutron Capture Therapy (BNCT), because the soft spectrum requires less moderation than those from other neutron production reaction such as 9Be(p,n), 9Be(d,n), and so on. Such lithium target is composed of lithium layer on the substrate.
Under the beam current so as to complete neutron source for accelerator based BNCT, lithium metal has poor characteristics as neutron target, because lithium has low adhesive strength, and thermal low melting point (181 degree Celsius). These poor characteristics indicate that lithium is easy to evaporate and peel off from the lithium layer surface. Then lithium make easily strong alkaline compound by reacting with air and water, which erode the accelerator parts, the vacuum pomp and so on. On the other hand, the radiation damages like blistering cause the separation of lithium and substrate, and degrade the heat removal from front lithium surface that will result in overheating of the lithium layer. Then lithium's low thermal conductivity (~70 W/m/K) makes thermal removal difficult. To overcome the problems as mentioned above, we have to develop the system with powerful cooling device and the mechanism for prevention of splash of lithium.
Our target system is composed of multi-layer on the cooling device. The combination of protection material, lithium and hydrogen absorbing alloys makes the multi-layer. To avoid the separation of each material at the interface of layers, we applied functional degrade material (FGM) to the binder. The cooling device is composed of the target
substrate and cooling water. Copper is selected as a target substrate owing to good thermal conductivities (386 W/m/K at room temperature).
With a view to remove heat sufficiently, the thick cooling water layer is required, but neutrons decrease by interactions with the water. Therefore, we need to make the water thickness smaller to keep neutron intensity. Instead of making the cooling water thickness larger, we make the cooling area wider by adding pins on the behind of target substrate. The optimization to arrange pins by calculation based on heat transfer engineering theory makes the area of cooling twice that of substrate without pins.
To inspect our design, the beam experiment was performed. We utilized the Neutron Exposure Accelerator System for Biological Effect Experiments (NASBEE), National Institute of Radiological Sciences (NIRS), Japan. This facility can provide proton and deuteron beams of up to 800 micro-A and 600 micro-A, respectively. Then we also developed the beam port so that the beam power density of 200 W/cm2 are obtained. We have also developed beam monitor by referring the surface temperature. As an evaluation of thermal removal, we referred to temperature variation of copper backing by varying the proton beam current. The temperature of target surface was 140 degrees Celsius, and no blistering is observed, when beam power was 200 W/cm2. Evaluation results indicate that our target system realize the low energy intense neutron source with lithium., 15th International Congress on Neutron Capture Therapy},
 title = {Development of Target system for intense neutron source of p-Li reaction},
 year = {2012}
}