A buffer-free concept bubble chamber for PICO dark matter searches

• Published in: Journal of instrumentation Vol. 14; no. 8; p. P08019
• Main Authors: Bressler, M., Campion, P., Cushman, V.S., Morrese, A., Wagner, J.M., Zerbo, S., Neilson, R., Crisler, M., Dahl, C.E.
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 19.08.2019; Institute of Physics (IOP)
• Subjects: Alpha decay; Bellows; Bubble chambers; Buffer layers; Cesium 137; Cesium isotopes; Chambers; Dark matter; Dark Matter detectors; Decay rate; detector design and construction technologies and materials; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; liquid detectors; Liquid-liquid interfaces; neutron detectors; Perfluorocarbons; Prototypes; Recoil; Searching; Stereoscopy; Surface tension; Thresholds; Weakly interacting massive particles
• ISSN: 1748-0221; 1748-0221
• DOI: 10.1088/1748-0221/14/08/P08019

In this paper, we report on the successful operation at Drexel University of the PICO collaboration's first C3F8 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 C3F8 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 137Cs gammas and spontaneous fission neutrons from 244Cm, 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.