Synthesis of high-strength, radiopure, electroformed copper-based alloys for rare-event searches: A materials design perspective

Abstract: Rare-event searches are key to unveiling the constituents of dark matter and to understanding the nature of neutrinos. These endeavors demand detectors with exceptionally low levels of radioactivity, leading to breakthroughs in related techniques. In this context, additive-free electroformed copper has emerged as the material of choice thanks to its excellent radiopurity, favorable physical properties, and affordable cost. However, its high ductility and limited mechanical strength pose challenges for its use in detectors. Recently, electroformed copper-chromium alloys have been proposed, with early investigations suggesting that small chromium admixtures lead to enhanced strength while maintaining radiopurity. Electroformed copper-based alloys are investigated from a materials design perspective to address current challenges and optimize the processing of materials. Modeling tools based on computational thermodynamics are used to predict material properties following thermal processing. In addition to chromium, the use of titanium as an additional alloying component for superior mechanical strength is explored. The findings suggest a path towards the design of high-performance, radiopure copper-based alloys suitable for next-generation rare-event experiments, while minimizing lengthy and expensive trial-and-error approaches. The impact on future experiments is exemplified through the case of the DarkSPHERE and XLZD experiments.