  In this paper, we report on the successful operation at Drexel University of
the PICO collaboration's first C$_3$F$_8$ buffer-free prototype fluorocarbon
bubble chamber. Previous PICO bubble chambers have produced world-leading WIMP
search results with fluorocarbon target fluids, separated from the steel
bellows by a buffer layer of water. Surface tension effects at the jar walls
and liquid-liquid interface lead to a class of background events which have
nuclear-recoil-like acoustic signatures and thus contaminate the WIMP-like
signal region in analysis. Thus new bubble chambers are to be constructed
"right-side-up", meaning that the jar of C$_3$F$_8$ is above the bellows with
no water inside the inner vessel. The Drexel Bubble Chamber (DBC), runs
successfully at and below the nuclear recoil thresholds used by PICO for WIMP
searches, including thresholds as low as 1.19 keV. We have demonstrated
sensitivity to $^{137}$Cs gammas and spontaneous fission neutrons from
$^{244}$Cm, and acoustic alpha discrimination is demonstrated to be possible
although the observed rate of alpha decays is very low. Position reconstruction
from stereoscopic imaging allows for basic analysis cuts for calibration data.
The successful construction and operation of this prototype confirm the
effectiveness of the right-side-up design, which will be used in future dark
matter searches such as PICO-40L and PICO-500.
