The SIMPLE Dark Matter project is an experiment to search for direct evidence of dark matter. It is located at LSBB in France: it consists of an international collaboration with members from Portugal, France, and USA. It uses Superheated Liquid Detectors, with the refrigerant – freon C2ClF5 - being the active mass. SIMPLE is predominantly sensitive to spin-dependent interactions of WIMPs (Weakly Interacting Massive Particles).
A Superheated Droplet Detector (SDD) is a suspension of micrometric superheated freon droplets inside a viscous elastic gel, which undergo transitions to the gas phase upon energy deposition by incident radiation: each droplet behaves as a miniature bubble chamber. The detector can stay active for much longer periods than a classic bubble chamber. The SIMPLE dark matter detectors are generally of 1-2% freon concentrations, fabricated from food gels comprise a device that is almost insensitive to common background radiations. The sensitivity of the detectors can be adjusted by changing the temperature and pressure of each device. Once a nucleation has occurred, the acoustic shock wave is recorded by microphones. Each acquired signal is then fully discriminated in terms of acoustic external noise, gel associated noise and most recently particle-induced nucleations.
The next phase of SIMPLE involves the transition from SDD to Bubble Chamber (BC), with a re-sitting of the measurements to the LSBB Capsule in order to accommodate a factor 2 increase in the detector neutron shielding thickness.