They stick it underground in a gold mine and the other reason they stick underground is to prevent cosmic ray and to insulate it from all kinds of noise. and once in a very long while an electron neutrino, penetrating this tank of chlorine will interact with a neutron and a chlorine atom and convert that neutron, through the reaction that we talked about, where an electron neutrino plus a neutron can become a proton plus an electron. through that reaction this occurs inside the nucleus that converts one of the neutrons here to a proton that converts chlorine to an radioactive, unstable isotope of argon, a noble gas. 