Project: datamanagement
Issue DM-6030: Investigate possibilty of cosmic ray muons (etc) for precision gain calibration
In the era of CBPs, we care about absolute system throughput, and thus need to accurately know the gain of amplifiers in the CCDs. Initially, this can be done by lab-based Fe55 characterisation (modulo the non-linearity, though that itself will need to be need to be characterised and corrected for), but changes in the relative gains of the various amplifiers need to be monitored, and this must be done in a way that is not degenerate with the optical transmission in any way. Theoretically it should be possible to use cosmic ray muon tracks, and tracks from radioisotope contamination of the glass/dewar, to measure the (change in the) relative gains of the amplifiers. Early work has shown that this does work in principle, but this ticket is for some further effort to see whether this method can provide the necessary accuracy given the amount of data available remains to be seen. This ticket would normally need to be significantly more points, but as it builds on earlier work, it can, at least for initial results, be done quite cheaply. Initial investigation will inform further work. 1st order: histogram all pixels in dark images after careful bias subtraction. Look at shape of spectrum. Fit some arbitrary function, and correlate with Fe55 gain measurements. 2rd order: Separate muon tracks from soft electron tracks/nuclear recoil events. Can cutting one of more of these types out improve the correlation? Or can treating them separately improve the resolution? 3rd order: Recalculate the histogram in terms of the dE/dx for the muon tracks, i.e. taking into account their track lengths and thus angle through the silicon.
Story points: 10