Hybrid Ultra-Low-Radioactive Material for Protecting Dark Matter Detector from Background Neutrons

Area of Science:

• Materials Science
• Nuclear Physics
• Particle Physics

Background:

• Direct dark matter detection experiments require materials with extremely low intrinsic radioactivity (ultra-low background).
• Hybrid materials (HM) combining neutron absorption and detection capabilities are crucial for next-generation underground detectors, particularly those using liquid noble gases.

Purpose of the Study:

• To develop a novel laboratory technology for an ultra-low background hybrid material (HM).
• To enable simultaneous neutron absorption and detection for enhanced sensitivity in dark matter searches.

Main Methods:

• Developed a method for determining 65 impurity elements using inductively coupled plasma mass-spectrometry (ICP-MS) with limits of determination (LD) of 0.011 ppb for uranium and 0.016 ppb for thorium.
• Synthesized and purified gadolinium(III) acetylacetonate (Gd(acac)₃) with U/Th content below LD.
• Fabricated gadolinium-doped polymethylmethacrylate (PMMA) via thermal polymerization of Gd(acac)₃ in methylmethacrylate for ultra-low background.

Main Results:

• Achieved LD of 0.011 ppb for uranium and 0.016 ppb for thorium in Gd-based preparations.
• Identified commercial Gd-based preparations with the lowest U and Th contents (1.2-0.2 ppb).
• Successfully produced Gd-doped PMMA with ultra-low background by purifying GdCl₃ and synthesizing Gd(acac)₃.

Conclusions:

• The developed laboratory technology and hybrid material meet the stringent requirements for neutron absorption and detection.
• The ultra-low background hybrid material is highly suitable for future low background underground detectors, especially for dark matter searches with liquid noble gases.