Cosmogenic activation of silicon

Le résumé fourni par la source

The production of $^{3}\mathrm{H}$, $^{7}\mathrm{Be}$, and $^{22}\mathrm{Na}$ 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 $(112\ifmmode\pm\else\textpm\fi{}24)\text{ }\mathrm{atoms}/(\mathrm{kg}\text{ }\mathrm{day})$ for $^{3}\mathrm{H}$, $(8.1\ifmmode\pm\else\textpm\fi{}1.9)\text{ }\text{ }\mathrm{atoms}/(\mathrm{kg}\text{ }\mathrm{day})$ for $^{7}\mathrm{Be}$, and $(43.0\ifmmode\pm\else\textpm\fi{}7.2)\text{ }\text{ }\mathrm{atoms}/(\mathrm{kg}\text{ }\mathrm{day})$ for $^{22}\mathrm{Na}$. 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 $(124\ifmmode\pm\else\textpm\fi{}25)\text{ }\text{ }\mathrm{atoms}/(\mathrm{kg}\text{ }\mathrm{day})$ for $^{3}\mathrm{H}$, $(9.4\ifmmode\pm\else\textpm\fi{}2.0)\text{ }\text{ }\mathrm{atoms}/(\mathrm{kg}\text{ }\mathrm{day})$ for $^{7}\mathrm{Be}$, and $(49.6\ifmmode\pm\else\textpm\fi{}7.4)\text{ }\text{ }\mathrm{atoms}/(\mathrm{kg}\text{ }\mathrm{day})$ for $^{22}\mathrm{Na}$. 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.

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