Development of Super Conducting Low Radioactivity flexible cables and circuitry (ULB-SSC)

A problem for rare-event physics experiments such as nEXO, LEGEND, NEXT, OSCURA, DAMIC, SuperCDMS, CRESST, and others is that they are exquisitely sensitive to the presence of ionizing radiation, particularly when it originates from radioactive contaminants trapped in nearby cabling/electronic circuitry. Ionizing radiation increases noise in the experiments, making it harder to distinguish actual events from background and lengthening, in some cases dramatically, the amount of time needed to for data collection. Sensitive semiconductor electronics, such as those used in avionics, and fragile qubits used in advanced quantum computing applications, are also sensitive to radioactivity from the same source. To address this issue, methods of manufacturing “radiopure” cabling/electronics have been the subject of intense R+D. In this approach, radioactive contaminants are either systematically and rigorously excluded (by careful selection of raw materials) or eliminated post facto (by cleaning and/or advanced industrial processing). The figure of merit for radiopurity is the presence, in parts per trillion, of the two most serious radioactive contaminants 238U and 232Th and their progeny. While progress has been made, a vetted, scalable and commercially implementable “best practices” method for manufacturing the required range of radiopure flexible cabling/electronics has yet to be fully demonstrated. In Phase I we investigated production of ultra-low radioactivity flexible cables and circuitry. By systematically eliminating sources of contamination in our production process, and implementing alternative cleaning methods, reduction in the presence of the radioactive elements 238U and 232Th by a factor of > 25x and > 10x, respectively, was demonstrated by state-of-the-art plasma mass spectroscopy (ICP-MS) testing at PNNL. In Phase II we systematically investigated and optimized critical radiopure manufacturing processes such as electroplating and ENIG. We designed, built and tested two microstrip prototype cables (one for nEXO, one for DAMIC); these protypes were the basis of the first commercial sale of 28 radiopure flexible cables to DAMIC. Another significant milestone was upgrading the ultrasonic cleaning bath to one 6.5 feet in length which was used in manufacturing the DAMIC cables. An additional advance in Phase II was that all cleaning steps were successfully transferred from PNNL– a very controlled, clean-room laboratory environment with trained analytical chemists working on small samples–to a scalable industrial setting without any cleanrooms and large volume cable fabrication equipment. This is an important enabling step in gearing up Q-Flex to commercially manufacture radiopure cables. In Phase IIB we will design and build a prototype 3-layer stripline cable and demonstrate similar levels of radiopurity (< 100 ppt U, Th, < 1000 ppb K) to the microstrip design that we have developed in Phase I and Phase II. A multilayer stripline cable is more complex and versatile than the microstrip cables that were built in Phase II. This new design will be used to enable experiments at nEXO and LEGEND and, along with the other accomplishments on this project to date, position Q-Flex as the pre-eminent supplier of radiopure flexible cables for the high energy physics, quantum computing, and semiconductor/avionics communities.