The Helium And Lead Observatory (HALO) is a

neutrino detector A neutrino detector is a physics apparatus which is designed to study neutrinos. Because neutrinos only Weak interaction, weakly interact with other particles of matter, neutrino detectors must be very large to detect a significant number of neut ...

SNOLab SNOLAB is a Canadian underground science laboratory specializing in neutrino and dark matter physics. Located 2 km below the surface in Vale's Creighton nickel mine near Sudbury, Ontario, SNOLAB is an expansion of the existing facilities con ...

for the Supernova Early Warning System (SNEWS). It began engineering operation on May 8, 2012, and joined as an operational part of SNEWS in October 2015. It was designed to be a low-cost, low-maintenance detector with limited capabilities sufficient for the burst of neutrinos generated by a nearby

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

. Its major components are left over from other decommissioned experiments: 76 tons of

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

from an earlier cosmic-ray experiment, and 128 three-metre-long

helium-3 Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (the most common isotope, helium-4, having two protons and two neutrons in contrast). Other than protium (ordinary hydrogen), helium-3 is the ...

neutron detector Neutron detection is the effective detection of neutrons entering a well-positioned detector. There are two key aspects to effective neutron detection: hardware and software. Detection hardware refers to the kind of neutron detector used (the most ...

s from the

Sudbury Neutrino Observatory The Sudbury Neutrino Observatory (SNO) was a neutrino observatory located 2100 m underground in Vale's Creighton Mine in Sudbury, Ontario, Canada. The detector was designed to detect solar neutrinos through their interactions with a large t ...

. The idea of using lead to detect

supernova neutrinos Supernova neutrinos are weakly interactive elementary particles produced during a core-collapse supernova explosion. A massive star collapses at the end of its life, emitting of the order of 1058 neutrinos and antineutrinos in all lepton flavo ...

was originally proposed in 1996 by Cliff Hargrove as the "lead astronomical neutrino detector" (LAND), and in 2004, Charles Duba, then a PhD student working on SNO, proposed re-using them for this purpose, prompting the renaming to HALO. Design of the current detector began in 2007. When an

electron neutrino The electron neutrino () is an elementary particle which has zero electric charge and a spin of . Together with the electron, it forms the first generation of leptons, hence the name electron neutrino. It was first hypothesized by Wolfgang Pauli ...

collides with a lead nucleus, it causes a nuclear transmutation that ends with a

neutron emission Neutron emission is a mode of radioactive decay in which one or more neutrons are ejected from a nucleus. It occurs in the most neutron-rich/proton-deficient nuclides, and also from excited states of other nuclides as in photoneutron emission and ...

. Lead does not absorb neutrons readily since ²⁰⁸Pb it has a " magic number" of both protons and neutrons, so the neutrons pass through to the ³He detectors. If enough neutrons are detected in a short time, an alert is generated. One limitation of the detector's design is its small size; due to the limited amount of surplus lead available, half of the neutrons generated escape before hitting a neutron detector. To mitigate this, it is surrounded by a layer of water to reflect some of the neutrons back in. Budget permitting, there are plans for a larger detector using 1000 t of lead and the remaining leftover ³He detectors (Due to lead's high density; 1000 t is a cube on a side, not an impractical size for underground installation.)

References

External links

* http://www.snolab.ca/halo/ {{coord, 46.4719, N, 81.1866, W, display=title Buildings and structures in Greater Sudbury