Overview
"Superconductivity Preservation in NbN Thin Films: The Role of Lead Coating Under Proton Irradiation" was developed by Team Spartacus as a 2025 submission to the CERN Beamline for Schools (BL4S) competition, which invites high school students worldwide to propose experiments using a real particle beam at CERN. The proposal investigates whether a lead (Pb) coating can protect niobium nitride (NbN) superconducting thin films from proton radiation damage.
Superconductivity depends on Cooper pairs — paired electrons travelling without resistance below a critical temperature. Proton-induced defects (dislocations, vacancies, interstitial atoms) act as scattering sites that break up Cooper pairs and destroy the superconducting state. NbN is particularly valuable because of its relatively high critical temperature of 17.3 K (compared with 9.2 K for NbTi and 9.3 K for Nb), making it a key material for superconducting nanowire single-photon detectors (SNSPDs), space applications, and next-generation quantum devices — yet it remains vulnerable to the intense radiation found in space and accelerator environments.
Proposed Experiment
- Pb-coated NbN samples cooled to ~4 K using CERN's liquid helium facility (or a closed-cycle cryocooler) to maintain the superconducting phase
- Proton irradiation in four stepped energy rounds: 0.5 GeV, 1.5 GeV, 4.5 GeV, and 13.5 GeV, with magnets adjusting beam energy
- Collimators focusing the ~2 cm diameter proton beam onto the sample
- Beam telescopes placed before and after the sample to measure proton energy and position pre- and post-interaction
- Electrical resistance and critical temperature recorded before and after each round as reference points
- Statistical analysis quantifying how proton irradiation affects the superconducting properties at each energy level
Predicted Outcomes
The team's theoretical predictions span the energy range: at 0.5 GeV, defect formation should be limited with minimal change to the critical temperature; at 1.5 GeV, Cooper pairs may begin to be affected with a slight Tc decrease; at 4.5 GeV, structural damage should become evident with a noticeable Tc drop; and at 13.5 GeV, defect density may rise enough to largely disrupt superconductivity. The experiment would determine how effectively the lead coating suppresses this damage — lead being a proven radiation shield thanks to its high atomic number, high density, and low cost.
Understanding this protection could contribute to more resilient superconducting components for scientific, aerospace, and medical technologies, and represents Terra Reform's most technically ambitious research direction.
Competition Context
CERN Beamline for Schools is an annual international competition hosted by CERN — one of the most prestigious student science competitions in the world — that gives winning teams access to a real CERN beamline, allowing them to simulate radiation conditions that are otherwise impossible to replicate. The proposal is supported by an extensive literature review spanning superconductivity theory, irradiation effects, and detector physics.