Poster at LRT Conference 2026.

Hydrofluoric acid-free Titanium etching for rare-event searches

An abstract and a copy of the poster can be found here.

Desription

This work contributes to the development of radiopure copper-alloys, stronger than electroformed copper (EFCu), but within radiopurity limits, required for the next-generation detectors for rare-event searches.

Rare-event search experiments require construction materials with high radiopurity to minimise background contributions. Thanks to its high mechanical strength, low density, machinability, and commercial availability in relatively radio-pure forms, titanium is a suitable material for structural elements in rare-event searches. To remove potential surface deposits, a chemical etching stage is usually undertaken. However, due to its chemical resistance, the etching of titanium conventionally requires hydrofluoric acid, which poses serious health and safety challenges, which are further exacerbated in deep underground laboratory settings. An alternative approach is proposed, which uses sulphuric acid. This talk will present tests performed with this method, including performance dependence on temperature and concentration, as well as roughness measurements performed with an optical microscope and the effect on the surface microstructure performed using a scanning electron microscope.

References

[1] D. Spathara, P. Knights, and K. Nikolopoulos, “Design of high-strength, radiopure, electroformed copperbased alloys for rare-event searches: Impact of layer configuration on heat treatments,”, Sep. 2025. arXiv: 2509.07406 [physics.ins-det].

[2] D. Spathara, P. Knights, and K. Nikolopoulos, “Materials design for the synthesis of high strength radiopure copper alloys for rare event detection,” Commun. Phys., vol. 8, no. 1, p. 464, 2025. doi: 10.1038/s42005- 025-02363-z arXiv: 2507.00799 [physics.ins-det].

[3] L. Balogh et al., Copper electroplating for background suppression in the NEWS-G experiment, 2021. doi: https://doi.org/10.1016/j.nima.2020.164844

[4] P. Knights, I. Manthos, K. Nikolopoulos, G. Rogers, D. Spathara, and P. Walters, “Hydrofluoric acid-free titanium etching for rare-event searches,”, Jun. 2026. arXiv: 2606.24524 [physics.ins-det].

[5] P. Knights, K. Nikolopoulos, G. Rogers, D. Spathara, and P. Walters, “Titanium for rare-event searches: Hydrofluoric acid-free etching,”, Aug. 2025. arXiv: 2508.21029 [physics.ins-det].

[6] S. Ban, Y. Iwaya, H. Kono, and H. Sato, “Surface modification of titanium by etching in concentrated sulfuric acid,” Dental Materials, vol. 22, no. 12, pp. 1115–1120, 2006, issn: 0109-5641. doi: https://doi.org/10.1016/ j.dental.2005.09.007