AI 中文总结
本研究为SABRE-North实验评估四种NaI(Tl)探测器光学耦合材料，测量光学透过率与放射性纯度，发现无单一材料全面最优，需进一步测试以确定最终选择。
AI 中文摘要
直接暗物质探测使用NaI(Tl)闪烁体需要超低本底材料。硅胶光学垫片若能提供足够的光学透过率和放射性纯度，可将NaI(Tl)晶体与光电倍增管（PMT）耦合。我们为SABRE-North实验表征了四种候选材料：商用EJ-560（作为参考）以及三种在萨伦托大学生产的材料（SYLGARD 184、EGel 3002 A/B和一种混合配方），采用不同的催化剂比例和固化条件，共制备十个样品。通过紫外/可见/近红外分光光度法测量了310至850 nm的光学透过率。放射性纯度在LNGS的STELLA设施使用高纯锗（HPGe）γ射线能谱法评估，对于EJ-560还使用高分辨率ICP-MS。在410 nm的NaI(Tl)发射峰处，EJ-560的吸光系数为$0.064\pm0.017$ mm$^{-1}$。本地生产的最佳样品中，SYLGARD 184（10:2基料与催化剂比例）在室温和40°C固化时分别达到$0.097\pm0.015$和$0.093\pm0.014$ mm$^{-1}$，EGel 3002（2B:A比例）在40°C固化时为$0.125\pm0.015$ mm$^{-1}$，混合配方10:1 EGel A:CataSYL在室温固化时为$0.106\pm0.014$ mm$^{-1}$。EJ-560检测到约1.8 mBq/kg的$^{232}$Th链活度，且$^{40}$K活度最高，为$(120\pm20)$ mBq/kg。本地生产的材料未检测到Th链污染，但$^{226}$Ra活度约为2.3 mBq/kg，且$^{40}$K水平较低。没有单一材料在所有标准下均最优。需要额外的ICP-MS筛查、固化垫片的HPGe测量以及直接的NaI(Tl)-PMT光产额测试，才能最终确定SABRE-North的材料选择。
英文摘要
Direct dark matter detection with NaI(Tl) scintillators requires ultra-low-background materials. Silicone optical pads can couple NaI(Tl) crystals to photomultiplier tubes (PMTs) if they provide adequate optical transmission and radiopurity. We characterize four candidate materials for the SABRE-North experiment: commercial EJ-560, used as a reference, and three materials produced at the University of Salento (SYLGARD 184, EGel 3002 A/B, and a hybrid formulation) using different catalyst ratios and curing conditions, yielding ten samples in total. Optical transmittance was measured from 310 to 850 nm by UV/Vis/NIR spectrophotometry. Radiopurity was assessed at the STELLA facility at LNGS using high-purity germanium (HPGe) $γ$-ray spectrometry and, for EJ-560, high-resolution ICP-MS. At the 410 nm NaI(Tl) emission peak, EJ-560 shows an absorbance coefficient of $0.064\pm0.017$ mm$^{-1}$. The best locally produced samples reach $0.097\pm0.015$ and $0.093\pm0.014$ mm$^{-1}$ for SYLGARD 184 with a 10:2 base-to-catalyst ratio cured at room temperature and at $40^\circ$C, respectively, $0.125\pm0.015$ mm$^{-1}$ for EGel 3002 with a 2B:A ratio cured at $40^\circ$C, and $0.106\pm0.014$ mm$^{-1}$ for the hybrid 10:1 EGel A:CataSYL formulation cured at room temperature. EJ-560 exhibits detectable $^{232}$Th-chain activity at about 1.8 mBq/kg and the highest $^{40}$K activity, $(120\pm20)$ mBq/kg. The locally produced materials show no detectable Th-chain contamination but exhibit $^{226}$Ra activities of about 2.3 mBq/kg and lower $^{40}$K levels. No single material is optimal across all criteria. Additional ICP-MS screening, HPGe measurements of cured pads, and direct NaI(Tl)-PMT light-yield tests are required for a conclusive SABRE-North material selection.
