A new method of X-ray polarimetry based on the photoeffect and measuring the photoelectron emission direction in a finely segmented MOS CCD has been established with monochromatic synchrotron radiation of known linear polarization. For square pixels of 6.8 micrometer an analyzing power in the order of 10% has been measured at energies above 10 keV. A steep rise with energy is observed in accord with Monte Carlo simulations. In addition to small charge deposits due to the photoeffect in the thin depleted front layer of the CCD, also diffusion spread charge clusters from the much more abundant conversions deeper inside the chip were found to be very useful for simultaneous measurements of the polarization vector, the energy and the position on a photon-by-photon basis. In a first application of spatially and energetically resolved polarimetry the linear polarization of Parametric X- radiation (PXR) produced by 80.5 MeV electrons in a 13 micrometer thick silicon single crystal has been analyzed. The experiment was carried out at the Darmstadt superconducting linear accelerator S-DALINAC providing a low-emittance electron beam. The linear polarization of the (220) reflex observed in 8 narrow angular bins between 20 degrees and 21 degrees with respect to the electron beam direction is consistent with complete local linear polarization. The orientation of the polarization plane, within measurement errors of typically 10 degrees, varies over the diffraction pattern in such a way as to be expected from kinematical theory. The result of this experiment is in contradiction to the only other PXR polarization measurement performed so far.

Date Published: 17 December 1998
PDF: 12 pages
Proc. SPIE 3443, X-Ray and Ultraviolet Spectroscopy and Polarimetry II, (17 December 1998); doi: 10.1117/12.333604

Published in SPIE Proceedings Vol. 3443:
X-Ray and Ultraviolet Spectroscopy and Polarimetry II
Silvano Fineschi, Editor(s)