Cosmogenic activation of silicon

• Published in: Physical review. D 2020-11, Vol.102 (10), p.1, Article 102006
• Main Authors: Saldanha, R., Thomas, R., Tsang, R. H. M., Chavarria, A. E., Bunker, R., Burnett, J. L., Elliott, S. R., Matalon, A., Mitra, P., Piers, A., Privitera, P., Ramanathan, K., Smida, R.
• Format: Article
• Language: English
• Subjects: astroparticle detectors; ATOMIC AND MOLECULAR PHYSICS; Atoms & subatomic particles; Cosmic rays; Detectors; Neutron beams; Neutrons; nucleon induced nuclear reactions; particle dark matter; Particle physics; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; radiation detectors; Sea level; Silicon; Sodium 22
• ISSN: 2470-0010; 2470-0029
• DOI: 10.1103/PhysRevD.102.102006

The production of 3H, 7Be, and 22Na by interactions of cosmic-ray particles with silicon can produce radioactive backgrounds in detectors used to search for rare events. Through controlled irradiation of silicon CCDs and wafers with a neutron beam that mimics the cosmic-ray neutron spectrum, followed by direct counting, we determined that the production rate from cosmic-ray neutrons at sea level is ( 112 ± 24 )   atoms / ( kg   day ) for 3H, ( 8.1 ± 1.9 )     atoms / ( kg   day ) for 7Be, and ( 43.0 ± 7.2 )     atoms / ( kg   day ) for 22Na. Complementing these results with the current best estimates of activation cross sections for cosmic-ray particles other than neutrons, we obtain a total sea-level cosmic-ray production rate of ( 124 ± 25 )     atoms / ( kg   day ) for 3H, ( 9.4 ± 2.0 )     atoms / ( kg   day ) for 7Be, and ( 49.6 ± 7.4 )     atoms / ( kg   day ) for 22Na. These measurements will help constrain background estimates and determine the maximum time that silicon-based detectors can remain unshielded during detector fabrication before cosmogenic backgrounds impact the sensitivity of next-generation rare-event searches.