[neutralino]

Neutrinos are one of the fundamental particles that make up the universe. They are similar to the electron, however have no electric charge, and so are not affected by the electromagnetic force. They have a minute mass, if any, and so travel very close to the speed of light, and are incredibily unreactive. Quantities of neutrinos were created a few minutes after the big bang, and others are the byproducts of interstellar fusion. Neutrinos are a very useful tool for probing the universe, since they are unaffected by galactic magnetic fields, and do not interact with intergalactic material, or the CMB (Cosmic Microwave Background radiation). Here is a chart (from [1]) showing the energy scales over which neutrinos exist as opposed to other particles such as photons.

However, the same antisocial traits that make ultra high energy neutrinos favourable as astronomical messengers also make them incredibly difficult to detect. In this post I shall introduce two observatories, namely the Antarctic Muon and Neutrino Detector Array (AMANDA)[1] and its successor IceCube[2].

AMANDA is the largest currently operational detector for studying neutrinos. It was opened in 1997, and is based in Antarctic, near the south pole. It consists of strings of detectors buried between 1500m and 2000m below the ice. Currently under construction at the south pole is the massive IceCube detector; the detector for which AMANDA was a prototype. It is both larger and more advanced than its predecessor and, when operational, will consist of 10 times more detectors than AMANDA, covering a volume of a cubic metre of ice.

The following (from [4]) is an artist's impression of what the site will look like when IceCube has been completed.

Billions of neutrinos travel through our bodies each second. But since neutrinos rarely interact with anything, free-streaming through the space in between the atoms in molecules, the electrons and nuclei of atoms, and even the protons and neutrons of the highly dense atomic nuclei, you might go through your entire life span and never have a single atom in your body be impacted by a neutrino. However, the larger the object in question, the greater the chance that a neutrino will randomly bump into one of the molecules within the object. AMANDA and IceCube use their large size to try and intercept as many neutrinos as possible.

When a neutrino collides into a particle in the ice, it is converted into a heavier lepton (either an electron, muon or tau) and radiation. This lepton will give off light as it passes through the ice, and this light will be detected by either AMANDA's or IceCube's sensors. Scientists can then, from the detection of this light, build up a picture of how much energy the neutrino had on impact. An important thing about both AMANDA and IceCube is that they are built underground in an attempt to shield as much background radiation as possible, and so greater increase the chances of detecting neutrinos.

References
[1]AMANDA
[2]IceCube
[3]What is a neutrino?
[4]Introdcution to Neutrino Astronomy

Thanks to Mike 5 for this suggestion.

[neutralino]

The above post is a summary of both the AMANDA and IceCube observatories. Please add your comments about these, or about any other neutrino observatories that have been operational in the past.