This reduction may depend on the neutrino energy, inferred experimentally from the thresholds of the individual detectors. Out of all these neutrinos only a few of them a day are detectable. Minimizing the background radiation means reducing any sort of radiation that could give false neutrino events. Radon is a major type of radiation that could possibly give false neutrino events. Cosmic rays and even natural radioactivity from materials and the natural surroundings can also lead to fake events.
Neutrinos interact with charged particles which can be detected.
For example, a neutrino can impart it's energy to an atomic electron. KamLAND is capable of detecting these interactions as they happen. Scientists care about whether or not a neutrino has mass for a variety of reasons. If a neutrino has a mass, it may account for part of hot dark matter. A lot of cosmologists are very interested in whether or not neutrinos have mass because it will help explain a lot of things concerning the universe's origin.