  We report the performance of a 10 atm Xenon/trimethylamine time projection
chamber (TPC) for the detection of X-rays (30 keV) and gamma-rays (0.511-1.275
MeV) in conjunction with the accurate tracking of the associated electrons.
When operated at such a high pressure and in 1%-admixtures, trimethylamine
(TMA) endows Xenon with an extremely low electron diffusion (1.3 +-0.13
mm-sigma (longitudinal), 0.8 +-0.15 mm-sigma (transverse) along 1 m drift)
besides forming a convenient Penning-Fluorescent mixture. The TPC, that houses
1.1 kg of gas in its active volume, operated continuously for 100 live-days in
charge amplification mode. The readout was performed through the recently
introduced microbulk Micromegas technology and the AFTER chip, providing a 3D
voxelization of 8mm x 8mm x 1.2mm for approximately 10 cm/MeV-long electron
tracks. This work was developed as part of the R&D program of the NEXT
collaboration for future detector upgrades in the search of the 0bbnu decay in
136Xe, specifically those based on novel gas mixtures. Therefore we ultimately
focus on the calorimetric and topological properties of the reconstructed
MeV-electron tracks.
