ELUSIVE PARTICLES CAPTURED IN CLEANING FLUID
Neutrinos rarely interact with matter and are therefore very difficult to detect. However, a high energy neutrino can sometimes turn a chlorine atom into a radioactive argon atom, which is easy to detect. Raymond Davis Jr placed an enormous tank filled with chlorine-rich cleaning fluid in a deserted gold mine. Davis devised an ingenious method to collect and count the argon atoms produced in the tank – an almost impossible task since there were so few of them.

By pumping helium gas through the tank, Davis was able to flush out the argon atoms and count them as they decayed.

Expected number of neutrinos