X-ray polarimetry — A novel application of CCDs

A new method of X-ray polarimetry based on measuring the photoelectron emission direction in a finely segmented MOS CCD has been established using monochromatic synchrotron radiation and planar channeling radiation. For the smallest pixel dimensions (6.8 × 6.8 μm2) available today in commercial optical CCD cameras an analyzing power for linear polarization in the order of 10% has been measured at energies above 10 keV. A strong rise with energy is observed in accord with expectations from Monte Carlo simulations. In addition to events due to the photoeffect in the thin depleted front layer of the CCD, also diffusion spread events resulting from much more abundant conversions deeper inside the chip were found to be very useful for simultaneous measurements of polarization, energy and position.