  We devised and built a light, compact and transportable X-ray polarized
source based on the Bragg diffraction at nearly 45 degrees. The source is
composed by a crystal coupled to a small power X-ray tube. The angles of
incidence are selected by means of two orthogonal capillary plates which, due
to the small diameter holes (10 um) allow good collimation with limited sizes.
All the orders of diffraction defined by the crystal lattice spacing are
polarized up to the maximum order limited by the X-ray tube voltage. Selecting
suitably the crystal and the X-ray tube, either the line or the continuum
emission can be diffracted, producing polarized photons at different energies.
A very high degree of polarization and reasonable fluxes can be reached with a
suitable choice of the capillary plates collimation.
  We present the source and test its performances with the production of nearly
completely polarized radiation at 2.6, 5.2, 3.7 and 7.4 keV thanks to the
employment of graphite and aluminum crystals, with copper and calcium X-ray
tubes respectively. Triggered by the very compact design of the source, we also
present a feasibility study for an on-board polarized source, coupled to a
radioactive Fe55 nuclide and a PVC thin film, for the calibration of the next
generation space-borne X-ray polarimeters at 2.6 and 5.9 keV.

Astrophysics