Preliminary test of topmetal-II− sensor for X-ray polarization measurements

We present the assembly and preliminary results of a prototype detector, which was developed to evaluate the performance of the Topmetal-II− for application in Soft X-ray Polarimeter (SXP). SXP is used to measure the polarization of X-rays emitted from randomly occurring gamma-ray bursts (GRBs) and other specific dense celestial bodies. The Topmetal-II− is a silicon pixel sensor designed to directly track charged particles. The test was conducted on a gas mixture of Ne and DME at 0.8 atm pressure, and the Topmetal-II− sensor was used to image the photoelectron tracks. Typical real X-ray tracks obtained under four conditions are presented in this paper. The modulation factor derived from the tracks of 100% polarized 4.5 keV X-rays reached ∼ 29% at ∼ 53% signal efficiency, with a residual modulation of the order of ∼ 2% for unpolarized 5.9 keV X-rays.