PICASSO

The PICASSO (Project in Canada to Search for Supersymmetric Objects) experiment is an experiment searching for direct evidence of dark matter. It is located at SNOLAB in Canada, and consist of an international collaboration with members from the Université de Montréal, Queen's University, Indiana University South Bend and Czech Technical University in Prague, University of Alberta, Laurentian University and BTI, Chalk River, Ontario. It uses bubble detectors with Freon as the active mass. PICASSO is predominantly sensitive to spin-dependent interactions of Weakly Interacting Massive Particles (WIMPs) with fluorine atoms.

Principle

A bubble detector is a radiation sensitive device that uses small droplets of superheated liquid that are suspended in a gel matrix. It uses the principle of a bubble chamber but since only the small droplets can undergo a phase transition at a time, the detector can stay active for much longer periods than a classic bubble chamber. When enough energy is deposited in a droplet by ionizing radiation the superheated droplet undergoes a phase transition and becomes a gas bubble. The PICASSO detectors contain Freon droplets with an average diameter of . The bubble development in the detector is accompanied by an acoustic shock wave that is picked up by piezo-electric sensors. The main advantage of the bubble detector technique is that the detector is...
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