Transfer to impurities

Calibration of the impurity levels is done by finding capture events after the muon stop when known levels of impurities are present and then comparing this to the same anaysis in the final data. These capture events will be analyzed both in the main TPC data stream but also with FADC data specially triggered on events where a large second signal occurs after the muon stop. Both the time distribution of transfers, and the amount will be determined by this analysis. If these control measurements confirm the design gas purity of $<10^{-8}$ no correction needs to be made. Otherwise, the complete knowledge of this process will allow us to correct for the small time distortions created in our main spectrum. The two impurity atoms we expect to contend with are Nitrogen and Oxygen. Since their effects are similar a small correction can be made without reference to the ratio. If the correction is larger we will have to differentiate between the two using the transfer rate measured and slight differences in the energy distribution of the capture events.