Measurement of neutron activation of tritium in silicon using CCDs.

A major source of background in next-generation silicon-based dark matter experiments (such as DAMIC or SuperCDMS) is cosmogenic activation of tritium in the silicon detector material. Tritium is relatively long lived (compared to the time scale of dark matter experiments) and decays through a low energy beta decay, creating a significant irreducible background for silicon-based searches of low mass WIMPs or other low energy dark matter candidates. The cosmogenic activation rate of tritium in silicon is currently poorly understood, due the difficulties in measuring natural cosmogenic tritium contamination. An alternative method is to expose silicon to a high intensity neutron beam with a known spectrum similar to the natural cosmogenic spectrum and extrapolating the natural cosmogenic tritium activation rate from this much higher neutron exposure. We present results of exposing a silicon charge-coupled device (CCD) to the LANSCE neutron beam at Los Alamos and measuring the resulting tritium using the CCD directly.