Preparation of Isotopic ¹⁵⁰Sm and ¹⁴⁷Sm Nuclear Reaction Targets

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%.