A benign, low Z electron capture agent for negative ion TPCs

We have identified nitromethane (CH${}_3$NO${}_2$) as an effective electron capture agent for negative ion TPCs (NITPCs). We present drift velocity and longitudinal diffusion measurements for negative ion gas mixtures using nitromethane as the capture agent. Not only is nitromethane substantially more benign than the only other identified capture agent, CS${}_2$, but its low atomic number will enable the use of the NITPC as a photoelectric X{}-ray polarimeter in the 1{}-10 keV band.