  Liquid-argon scintillation detectors are used in fundamental physics
experiments and are being considered for security applications. Previous
studies have suggested that the addition of small amounts of xenon dopant
improves performance in light or signal yield, energy resolution, and particle
discrimination. In this study, we investigate the detector response for xenon
dopant concentrations from 9 +/- 5 ppm to 1100 +/- 500 ppm xenon (by weight) in
6 steps. The 3.14-liter detector uses tetraphenyl butadiene (TPB) wavelength
shifter with dual photomultiplier tubes and is operated in single-phase mode.
Gamma-ray-interaction signal yield of 4.0 +/- 0.1 photoelectrons/keV improved
to 5.0 +/- 0.1 photoelectrons/keV with dopant. Energy resolution at 662 keV
improved from (4.4 +/- 0.2)% ({\sigma}) to (3.5 +/- 0.2)% ({\sigma}) with
dopant. Pulse-shape discrimination performance degraded greatly at the first
addition of dopant, slightly improved with additional additions, then rapidly
improved near the end of our dopant range, with performance becoming slightly
better than pure argon at the highest tested dopant concentration. Some
evidence of reduced neutron scintillation efficiency with increasing dopant
concentration was observed. Finally, the waveform shape outside the TPB region
is discussed, suggesting that the contribution to the waveform from
xenon-produced light is primarily in the last portion of the slow component.
