同位素150Sm和147Sm核反应靶的制备

Preparation of Isotopic 150Sm and 147Sm Nuclear Reaction Targets

  • 摘要: 通过库伦激发实验研究稀土区Sm系列同位素的核结构需要使用同位素150Sm和147Sm金属单质靶作为核反应靶。为将150Sm2O3147Sm2O3高效率地还原成150Sm和147Sm金属单质,设计和建立了新型还原与蒸馏装置,研究了Sm2O3的还原与蒸馏工艺,并成功将粉末状150Sm2O3147Sm2O3还原蒸馏成钟乳石状150Sm和147Sm。结果显示,Zr是一种优选的还原剂,密闭式水冷DLC/Cu针收集器的效果更好,最佳还原温度和还原时间分别为1500 ℃和30 min, 150Sm2O3147Sm2O3的还原收集效率分别为94.8%和95.3%,还原蒸馏过程几乎没有引入额外的杂质。采用滚轧技术制备自支撑同位素150Sm和147Sm单质靶,厚度分别为2.1 mg/cm2和2.3 mg/cm2,材料利用率均接近100%。采用碳弧-超短源衬距离转动衬底蒸发复合镀膜技术制备150Sm/C和147Sm/C靶,使用扫描电子显微镜研究蒸发电流对Sm靶表面质量的影响。结果显示,蒸发电流为75~80 A时沉积的Sm靶表面光洁度较好,无明显缺陷和液滴;C衬厚度为25 μg/cm2150Sm和147Sm靶厚度分别为255 μg/cm2和267 μg/cm2150Sm和147Sm的材料利用率分别为7.19%和7.32%。

     

    Abstract: The 150Sm and 147Sm isotopic targets are needed in the Coulomb excitation experiments to study the nuclear structure of Sm isotopes in the rare-earth region. A novel reduction-distillation apparatus was designed and established to efficiently reduce 150Sm2O3 and 147Sm2O3 to 150Sm and 147Sm, respectively. The high temperature reduction-distillation technique of Sm2O3 was studied, and successfully used to reduce and distill 150Sm2O3 and 147Sm2O3 powders to stalactite-shaped metallic 150Sm and 147Sm, respectively. The reduction temperature was measured by an infrared thermometer (CIT-1TD). The impurity element contents were tested before and after reduction-distillation using an inductively coupled plasma optical emission spectrometer (ICP-OES). The results show that Zr is preferably selected as the reducing agent, the closed-type water-cooled DLC/Cu needle is used as a better collector, the optimal reduction temperature and reduction time are respectively 1500 ℃ and 30 min, the reduction-distillation efficiencies of 150Sm2O3 and 147Sm2O3 are respectively 94.8% and 95.3%, almost no additional impurities are introduced during the reduction-distillation process. The self-supporting metallic 150Sm and 147Sm targets were prepared by rolling technique. During the whole rolling process, the clean stainless-steel clips were used as a transition in order to achieve high-efficiency rolling of 150Sm and 147Sm while minimizing impurity contamination, and the indoor humidity was maintained over 60% to prevent the 150Sm and 147Sm targets from ignition. The thickness values of self-supporting 150Sm and 147Sm targets were measured using a balance (XP2U, 0.1 μg), and their thickness uniformities were measured using a length gauge (ND280/CT2500, ±0.03 μm). The results show that the material utilization rate achieves nearly 100%, the thicknesses of self-supporting metallic 150Sm and 147Sm targets are respectively 2.1 mg/cm2 and 2.3 mg/cm2, and the thickness uniformities of self-supporting metallic 150Sm and 147Sm targets within the range of 20 mm×20 mm are respectively 95.7% and 97.4%. The 150Sm/C and 147Sm/C targets were prepared by the carbon arc-rotating substrate evaporation with ultra-short source-substrate distance composite coating technique. The carbon film thickness was measured online via a quartz crystal thin-film thickness monitor (SQM-160). The effect of evaporation current on the surface quality of the targets was studied by scanning electron microscope (SEM). The results show that the target deposited with an evaporation current of 75-80 A has a better surface finish, no obvious defects or droplets, the thicknesses of the 150Sm and 147Sm targets on the carbon substrates with 25 μg/cm2 are respectively 255 μg/cm2 and 267 μg/cm2, and the material utilization rates achieve respectively 7.19% and 7.32%.

     

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