The COUPP collaboration uses bubble chambers to search for dark matter in the form of Weakly Interacting Massive Particles, or WIMPs. The bubble chamber fluid is superheated so that the recoiling nucleus from a scattering WIMP will nucleate a single bubble. At this low level of superheat, the bubble chamber is completely insensitive to the gamma-ray and beta-decay backgrounds that plague other dark matter detectors. Alpha decays in the target fluid do nucleate bubbles, but these are distinguished from WIMP interactions based on their ultrasonic acoustic signature.
COUPP is currently operating a 4kg CF3I bubble chamber at SNOLAB, and will install a 60kg CF3I bubble chamber in the summer and fall of 2012.