The Helium And Lead Observatory (HALO) is a neutrino detector at SNOLab for the Supernova Early Warning System (SNEWS).
[3][4] It was designed to be a low-cost, low-maintenance detector[5] with limited capabilities[6]: 38 sufficient for the burst of neutrinos generated by a nearby supernova.
The idea of using lead to detect supernova neutrinos was originally proposed in 1996 by Cliff Hargrove as the "lead astronomical neutrino detector" (LAND),[7] and in 2004, Charles Duba, then a PhD student working on SNO, proposed re-using them for this purpose, prompting the renaming to HALO.
[2] When an electron neutrino collides with a lead nucleus, it causes a nuclear transmutation that ends with a neutron emission.
Budget permitting, there are plans for a larger detector using 1000 t of lead and the remaining leftover 3He detectors[5]: 13–18 (Due to lead's high density; 1000 t is a cube 4.45 m (14.6 ft) on a side, not an impractical size for underground installation.)