Cosmogenic activation of silicon

The production of H3, Be7, and Na22 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 H3, (8.1±1.9) atoms/(kg day) for Be7, and (43.0±7.2) atoms/(kg day) for Na22. 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 H3, (9.4±2.0) atoms/(kg day) for Be7, and (49.6±7.4) atoms/(kg day) for Na22. 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.