PICO
PICO Project
PICO is a collaboration working to directly detect WIMP dark matter by using bubble chambers to register recoiling nuclei. Super heated liquid C3F8 is kept in a quartz vessel. Even though the fluid is above its boiling point it will not become a gas without a nucleation point. After a particle strikes the nucleus of a fluorine atom, the ionized nucleus recoils, radiating heat causing a bubble to form explosively (Behnke, et al.). Cameras inside the chamber sense the bubbles. Software then instructs the pressurization system to cause an increase in pressure to extinguish the bubbles. By analyzing the number and location of bubbles formed one can narrow down the possible particles causing the bubble. By listening to the bubbles being formed, using piezoelectric transducers, the identity of the particles can also be determined. The experiment is carried out 2km underground at SNOLAB in central Ontario, CA. SNOLAB is located deep underground to shield the bubble chamber from cosmic rays, which would constantly cause irrelevant bubbles to form.
Listening to the bubble forming is essential for distinguishing a possible WIMP interaction from “noise” (bubbles caused by radioactive decays). Depending on the fluid used for the bubble chambers, the piezoelectric transducers are forced to endure temperatures as cold as -25°C and pressure pulses going from 1 atm to 20 atm in 40 ms. So a transducer must be constructed that can withstand these hardships. IU South Bend(IUSB), leads the efforts to design and fabricate these specialized sound sensors, and verify that they will survive these harsh conditions.
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