@article{b1c53c2ec3664109b605a089acb7dbff,
title = "Copper electroplating for background suppression in the NEWS-G experiment",
abstract = "New Experiments with Spheres-Gas (NEWS-G) is a dark matter direct detection experiment that will operate at SNOLAB (Canada). Similar to other rare-event searches, the materials used in the detector construction are subject to stringent radiopurity requirements. The detector features a 140-cm diameter proportional counter comprised of two hemispheres made from commercially sourced 99.99% pure copper. Such copper is widely used in rare-event searches because it is readily available, there are no long-lived Cu radioisotopes, and levels of non-Cu radiocontaminants are generally low. However, measurements performed with a dedicated 210Po alpha counting method using an XIA detector confirmed a problematic concentration of 210Pb in bulk of the copper. To shield the proportional counter's active volume, a low-background electroforming method was adapted to the hemispherical shape to grow a 500-µm thick layer of ultra-radiopure copper to the detector's inner surface. In this paper the process is described, which was prototyped at Pacific Northwest National Laboratory (PNNL), USA, and then conducted at full scale in the Laboratoire Souterrain de Modane in France. The radiopurity of the electroplated copper was assessed through inductively coupled plasma mass spectrometry (ICP-MS). Measurements of samples from the first (second) hemisphere give 68% confidence upper limits of <0.58µBq/kg (<0.24µBq/kg) and <0.26µBq/kg (<0.11µBq/kg) on the 232Th and 238U contamination levels, respectively. These results are comparable to previously reported measurements of electroformed copper produced for other rare-event searches, which were also found to have low concentration of 210Pb consistent with the background goals of the NEWS-G experiment.",
keywords = "Copper, Dark matter, Direct detection, Electroforming, Low background, Rare event",
author = "{NEWS-G Collaboration} and L. Balogh and C. Beaufort and R. Bunker and A. Brossard and Caron, {J. F.} and M. Chapellier and Corcoran, {E. C.} and Coquillat, {J. M.} and S. Crawford and Fard, {A. Dastgheibi} and Y. Deng and K. Dering and D. Durnford and I. Giomataris and P. Gorel and M. Gros and P. Gros and G. Gerbier and G. Giroux and O. Guillaudin and Hoppe, {E. W.} and I. Katsioulas and F. Kelly and P. Knights and L. Kwon and S. Langrock and P. Lautridou and Mols, {J. P.} and Navick, {X. F.} and Martin, {R. D.} and Muraz, {J. F.} and T. Neep and K. Nikolopoulos and P. O'Brien and R. Owen and Piro, {M. C.} and D. Santos and G. Savvidis and I. Savvidis and {de Sola Fernandez}, {F. Vazquez} and M. Vidal and R. Ward and M. Zampaolo and Anguiano, {S. Alcantar} and Arnquist, {I. J.} and {di Vacri}, {M. L.} and K. Harouaka and K. Kobayashi and Thommasson, {K. S.}",
note = "Funding Information: A portion of this work was funded by PNNL Laboratory Directed Research and Development funds under the Nuclear Physics, Particle Physics, Astrophysics, and Cosmology Initiative. The Pacific Northwest National Laboratory is a multi-program national laboratory operated for the U.S. Department of Energy (DOE) by Battelle Memorial Institute under contract number DE-AC05-76RL01830 . This project has received funding from the European Union{\textquoteright}s Horizon 2020 research and innovation programme under the Marie Sk{\l}odowska-Curie grant agreement DarkSphere (grant agreement No. 841261 ). Support has been received from the Royal Society International Exchanges Scheme . This research was undertaken, in part, thanks to funding from the Canada Excellence Research Chairs Program , the Canada Foundation for Innovation , the Arthur B. McDonald Canadian Astroparticle Physics Research Institute , and the French National Research Agency ( ANR-15-CE31-0008 ). The authors would like to thank the XMASS collaboration for the use of their XIA detector through the NEWS-G/XMASS collaborative agreement. Funding Information: A portion of this work was funded by PNNL Laboratory Directed Research and Development funds under the Nuclear Physics, Particle Physics, Astrophysics, and Cosmology Initiative. The Pacific Northwest National Laboratory is a multi-program national laboratory operated for the U.S. Department of Energy (DOE) by Battelle Memorial Institute under contract number DE-AC05-76RL01830. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sk?odowska-Curie grant agreement DarkSphere (grant agreement No. 841261). Support has been received from the Royal Society International Exchanges Scheme. This research was undertaken, in part, thanks to funding from the Canada Excellence Research Chairs Program, the Canada Foundation for Innovation, the Arthur B. McDonald Canadian Astroparticle Physics Research Institute, and the French National Research Agency (ANR-15-CE31-0008). The authors would like to thank the XMASS collaboration for the use of their XIA detector through the NEWS-G/XMASS collaborative agreement. Publisher Copyright: {\textcopyright} 2020",
year = "2021",
month = feb,
day = "1",
doi = "10.1016/j.nima.2020.164844",
language = "English",
volume = "988",
journal = "Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment",
issn = "0168-9002",
publisher = "Elsevier",
}