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'''Bubble chambers''' – The [[PICASSO]] (Project In Canada to Search for Supersymmetric Objects) experiment is a direct dark matter search experiment that is located at [[SNOLAB]] in Canada. It uses bubble detectors with [[Freon]] as the active mass. PICASSO is predominantly sensitive to spin-dependent interactions of WIMPs with the fluorine atoms in the Freon. COUPP, a similar experiment using trifluoroiodomethane(CF<sub>3</sub>I), published limits for mass above 20 GeV in 2011.<ref>{{cite journal |last1=Behnke |first1=E. |last2=Behnke |first2=J. |last3=Brice |first3=S. J. |last4=Broemmelsiek |first4=D. |last5=Collar |first5=J. I. |last6=Cooper |first6=P. S. |last7=Crisler |first7=M. |last8=Dahl |first8=C. E. |last9=Fustin |first9=D. |last10=Hall |first10=J. |last11=Hinnefeld |first11=J. H. |last12=Hu |first12=M. |last13=Levine |first13=I. |last14=Ramberg |first14=E. |last15=Shepherd |first15=T. |last16=Sonnenschein |first16=A. |last17=Szydagis |first17=M. |title=Improved Limits on Spin-Dependent WIMP-Proton Interactions from a Two Liter Bubble Chamber |journal=Physical Review Letters |date=10 January 2011 |volume=106 |issue=2 |doi=10.1103/PhysRevLett.106.021303 |arxiv=1008.3518 |bibcode=2011PhRvL.106b1303B |pmid=21405218 |page=021303|s2cid=20188890 }}</ref> The two experiments merged into PICO collaboration in 2012.
A bubble detector is a radiation sensitive device that uses small droplets of superheated liquid that are suspended in a gel matrix.<ref>{{Cite web |url=http://www.bubbletech.ca/radiation_detectors_files/bubble_detectors.html |title=Bubble Technology Industries |access-date=2010-03-16 |archive-date=2008-03-20 |archive-url=https://web.archive.org/web/20080320061130/http://www.bubbletech.ca/radiation_detectors_files/bubble_detectors.html |url-status=dead }}</ref> 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.{{clarify |reason=this would make more sense if it read 'only a small number of droplets' |date=March 2015}} When enough energy is deposited in a droplet by ionizing radiation, the superheated droplet becomes a gas bubble. The bubble development 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 almost insensitive to background radiation. The detector sensitivity can be adjusted by changing the temperature, typically operated between 15 °C and 55 °C. There is another similar experiment using this technique in Europe called
PICASSO reports results (November 2009) for spin-dependent WIMP interactions on <sup>19</sup>F, for masses of 24 Gev new stringent limits have been obtained on the spin-dependent cross section of 13.9 pb (90% CL). The obtained limits restrict recent interpretations of the DAMA/LIBRA annual modulation effect in terms of spin dependent interactions.<ref>{{cite journal |author=PICASSO Collaboration |title=Dark Matter Spin-Dependent Limits for WIMP Interactions on <sup>19</sup>F by PICASSO |journal=Physics Letters B |date=2009 |doi=10.1016/j.physletb.2009.11.019 |bibcode=2009PhLB..682..185A |volume=682 |issue=2 |pages=185–192 |arxiv=0907.0307|s2cid=15163629 }}</ref>
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