X-ray polarimetry with a micropattern TPC

The micropattern time projection chamber (TPC) offers a novel method of imaging the tracks of photoelectrons as a means of X-ray polarimetry with the potential to simultaneously achieve large modulation factors and high quantum efficiency. Measurements with a simple prototype micropattern TPC polarimeter, with an 18 mm-atm absorption depth of a mixture of 50% neon and 50% dimethyl ether, result in a modulation factor of 45.0±0.6% with polarized 6.4 keV X-rays. With unpolarized 5.9 keV X-rays, the measured modulation factor is 0.49±0.54%, consistent with zero. The geometry of the TPC polarimeter will enable substantial improvements in quantum efficiency without the loss of modulation.