Poster presentation in IDM 2026, Spain.

Designing the next generation of materials for rare-event searches: high-strength, ultra-pure copper alloys

An abstract can be found here.

A video can be found here.

Presentation

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.

The manufacturing process includes electroforming and electroplating similar to the techniques utilised for EFCu. This is followed by thermal processing in two stages, aiming at:

1. homogenisation of alloy composition throughout the volume, and

2. aging to grow secondary phase precipitates for enhancing mechanical properties, like hardness and strength.

The modelling methods to optimise thermal processing parameters are based on computational thermodynamics.

Thermodynamic behaviour of each species and their in-between interactions will indicate the single phase at which we can expect homogenisation; i.e. the temperatures for composition range we aim at the 1st stage of thermal processing. The thermodynamic and kinetic description of the system will inform the temperature - time relation to achieve maximum mechanical strength during the 2nd stage of thermal processing.

Mechanical enhancement of Cu fcc matrix is achieved at the first stage by lattice distortion, when some sites of the fcc crystal structure are occupied by Cr atoms of different radius. During the aging stage, as Cr atoms will leave these sites to form spherical precipitates of the bcc phase, the solid solution strengthening achieved previously will decrease, but precipitates of the other phase will act as barriers for any disslocations movement. Maximum yield strength can be achieved when these precipitates form at the smallest radius and are uniformly dispersed in the fcc matrix.

We demonstrated that previous attempts to synthesise radiopure CuCr alloys, aiming at 0.5 wt% in Cr, were carried out at temperatures lower than the single-phase. Also, according to our simulations, the chosen layer configuration would only lead to maximum 0.2 wt% Cr content in the alloy. This means that the volume fraction of the bcc phase would be even lower. Additionally, aging was carried out at 500°C for 12 hours. Our simulations indicate that even for higher volume fractions, mechanical strength will be halved after less than two hours, and maximum enhancement could be achieved in less than one hour.

We propose a methodology for optimising the manufacturing parameters (i.e. layer/configuration for electroplating and time - temperature for thermal processing) using computational thermodynamics to manufacture CuCr and CuCrTi alloys with 0.5 wt% Cr content and the desired composition and mechanical strength.

The impact of our work has been explored in two different case studies. Here’s the one for DarkSPHERE project. Assuming we are able to manufacture a Spherical Proportional Counter made out of CuCr alloy with double the strength of EFCu, this would allow operation at 10 bar, leading to half the time required for data collection with a particular gas mixture, maximising the physics potential.

This is the first time a materials design approach using computational thermodynamics is proposed for manufacturing ultra-pure, high-strength alloys for detectors, used for rare-event searches.

References

[1] NEWS-G Collaboration “Copper electroplating for background suppression in the NEWS-G experiment”, Nucl. Instrum. Meth. A, 988 (2021): 164844

[2] NEWS-G Collaboration “Exploring light dark matter with the DarkSPHERE spherical proportional counter electroformed underground at the Boulby Underground Laboratory”, Phys. Rev. D 108, (2023): 112006

[3] Vitale A. et al. “A preliminary investigation into the electrodeposition and synthesis of radiopure Copper–Chromium alloys for rare-event physics detector systems”, Nucl. Instrum. Meth. A, 1003 (2021): 165291

[4] Spathara, D., “Design of high-strength, radiopure copper–chromium alloys for rare-event searches assisted by computational thermodynamics”, Nuclear Inst. and Methods in Physics Research, A, 1082 (2026): 170970

[5] Spathara, D., et al. “Materials design for the synthesis of high strength radiopure copper alloys for rare event detection”, Commun Phys 8 (2025): 464