A very compact polarizer for an X-ray polarimeter calibration

TL;DR

This paper presents a compact, transportable X-ray polarized source based on Bragg diffraction, capable of producing highly polarized X-rays at multiple energies for calibration purposes.

Contribution

The authors developed a novel, lightweight X-ray polarized source using crystal diffraction and capillary collimation, suitable for space-borne X-ray polarimeter calibration.

Findings

Achieved nearly complete polarization at multiple energies.

Demonstrated the source's performance with various crystals and X-ray tubes.

Proposed a feasible design for an on-board calibration source.

Abstract

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.