Photoelectron Track Length Distributions in CH$_{3}$OCH$_{3}$ and Ne:CO$_{2}$:NO$_{2}$CH$_{3}$

We have measured the photoelectron track length distribution in 190 Torr CH$_{3}$OCH$_{3}$ and 400 Torr Ne:CO$_{2}$:NO$_{2}$CH$_{3}$, partial pressures 300:80:20 Torr, using a Time Projection Chamber Polarimeter (TPC) and Negative Ion TPC Polarimeter (NITPC) respectively. The measurements were made at the Brookhaven National Laboratory National Synchrotroon Light Source. Track length means range from 150 microns at 2.5 keV to 700 microns at 6 keV for CH$_{3}$OCH$_{3}$ and 150 microns at 3.0 keV to 700 microns at 7 keV. The track length mean vs energy was found to fit a powerlaw as reported for other gases. We found that for CH$_{3}$OCH$_{3, }$n=1.69 and for Ne:CO$_{2}$:NO$_{2}$CH$_{3,}$ n=1.72. This data has important implications for the design of the readout in future TPC's and NITPC's. TPC's and NITPC's for X-ray polarization were recently developed at NASA GSFC and a CH$_{3}$OCH$_{3}$ TPC will be the main instrument for the GEMS mission, a recently selected NASA SMEX.