KamLAND hopes to obtain an accurate measurement of the 7 Be neutrino flux from the sun and compare results. There are various sources of possible contamination inside the KamLAND detector. Cosmic-muon induced processes and natural radioactivity from natural surroundings are the two possible candidates for false events. The time window can range from 10-500 m s and neutron capture should occur within 1 m of the vertex of the positron annihilation. Distinguishing what is really a neutrino event from other false signals is a very difficult task and a high priority for neutrino detection of any sort.
Underground detectors have the advantage of being mostly protected from cosmic rays.
KamLAND is shielded by 2700 mwe of rock. The scintillator itself is housed inside a cylindrical vessel containing ultrapure water acting as a veto counter. Any muon that transverses the veto detector will negate any event that occurs within 50 ms that is also within a reasonable distance of the muon detection. In addition, any muon detection inside the central detector will result in a 250 ms veto within reasonable proximity. By applying a conservative veto, KamLAND will reduce but not eliminate the possibility of fake events.