Making low radioactivity connections

Flexible printed cables and circuitry based on copper-polyimide materials are widely used in experiments looking for rare events, such as neutrinoless double beta decay, due to their unique electrical and mechanical characteristics. However, copper-polyimide flexible cables contain high levels of 238U, 232Th, and 40K, which can be a significant source of radioactive background for many current and next-generation ultralow background detectors.



In this talk I will present a comprehensive investigation into the fabrication process of copper-polyimide flexible cables and the development of custom low radioactivity cables for use in rare-event physics applications. A methodical step-by-step approach was developed and informed by ultrasensitive assay to determine the radiopurity in the starting materials and identify the contaminating production steps in the cable fabrication process. We have demonstrated a roughly 100x reduction in 238U and 20x reduction in 232Th compared to commercial cables, with the potential to significantly reduce radioactive backgrounds for neutrinoless double beta decay and dark matter experiments such as nEXO and Oscura.