Abstract
We report the performance of a 10atm Xenon/trimethylamine time projection chamber (TPC) for the detection of X-rays (30keV) and γ-rays (0.511–1.275MeV) 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±0.13mm-σ (longitudinal), 0.95±0.20mm-σ (transverse) along 1m drift) besides forming a convenient ‘Penning-Fluorescent’ mixture. The TPC, that houses 1.1kg of gas in its fiducial 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×8mm×1.2mm for approximately 10cm/MeV-long electron tracks. Resolution in energy (ε) at full width half maximum (R) inside the fiducial volume ranged from R=14.6% (30keV) to R=4.6%(1.275MeV).This work was developed as part of the R&D program of the NEXT collaboration for future detector upgrades in the search of the neutrino-less double beta decay (ββ0ν) 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. In particular, the obtained energy resolution has been decomposed in its various contributions and improvements towards achieving the R=1.4%1MeV/ε levels obtained in small sensors are discussed.
Highlights
The ability to perform γ-ray spectroscopy in conjunction with the accurate electron(s) reconstruction is of contemporary interest in fundamental science and technology
We report the performance of a 10 atm Xenon/trimethylamine time projection chamber (TPC) for the detection of X-rays (30 keV) and γ-rays (0.511–1.275 MeV) in conjunction with the accurate tracking of the associated electrons
A ‘dream’ scenario for detection is that where full event containment can be achieved in a medium with sparse ionization; an optimal (‘intrinsic’) energy resolution emerges from the subsequent sub-Poisson fluctuations of the released charge [7], while the sense of the momentum vector can be obtained through resolving distinct track features such as Bragg peak [8] or characteristic X-ray emission at production
Summary
The ability to perform γ-ray spectroscopy in conjunction with the accurate electron(s) reconstruction is of contemporary interest in fundamental science and technology. Such an asset is of utmost importance for instance in some implementations of Compton cameras either in standard [1] or electron-tracking mode [2], γ and X-ray polarimetry [3,4] as well as nuclear physics [5,6]. Reconstruction of the track's direction requires multiple scattering to be minimized and fidelity to the primary ionization trail to be ensured by proper design choices If such is the case, accurate information about the photon energy, direction and sense of its momentum vector, and about its polarization, can be retrieved from the emerging lepton track(s), involving in general multi-site cluster reconstruction algorithms. For very rare nuclear β-decays, on the other hand, an extremely high selectivity and background suppression can be achieved from the combined calorimetric and topological information [5]
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