Development of Ultra Low Radioactivity Cables and Circuitry

A problem for rare-event physics experiments such as nEXO, LEGEND, NEXT, OSCURA, DAMIC, SuperCDMS, and 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. 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 radiopure cabling/electronics has yet to be fully demonstrated. In Phase I we investigated production of ultra-low radioactivity flexible cables and circuitry. Specifically, we systematically determined and eliminated sources of contamination in our production process, and studied alternative methods—such as new cleaning chemicals—to minimize radioactivity in the cabling. A 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. Phase II will continue the work begun in Phase I by accomplishing three principal Aims: Aim I: Continue the work done in Phase I by studying those cable production steps that were identified as being significant sources of contamination. Optimize the Q-Flex cable production process to minimize overall radioactive contamination. Significantly, in this Aim we will for the first time employ germanium detection to determine the presence of any radioactive progeny along with via ICP-MS the level of 238U and 232Th in ppt. Aim II: Using the “best practices” radiopurity process optimized in Aim I, produce a test batch of 10 x prototype cables, suitable for use on nEXO and LEGEND particle detection projects. Aim III: Scale up to produce a working set (N = 100) customized radiopure cables suitable for use on the nEXO project. Development of radiopure manufacturing is expected to have strong commercial benefits as well. For example, ionizing radiation is also deleterious to advanced semiconductor fabrication. Similarly, the role of ionizing radiation in limiting the performance of quantum computers is just being appreciated. Phase II will fully establish a robust and reliable method for producing radiopure cables and circuitry which can then be immediately employed to aid the search for neutrino less double beta decay as well as other low-background applications such as dark matter searches. Upon vertical integration of a vetted manufacturing process, we also anticipate significant commercial benefits in the sale of radiopure products into established QFlex customers in the semiconductor and quantum computing sectors.