The Neutrino Telescope at the South Pole

----------------- #1219 - ICECUBE - Neutrino Telescope at the South Pole
- An amazing new telescope was constructed inside of glacier ice at the South Pole. It is designed to detect Neutrinos and to study sources of nuclear fusion and Cosmic Rays throughout the Cosmos. This review describes how the telescope was built, how it works, and what it expects to discover.

- Attachment: cosmic rays

- ICECUBE is a Neutrino telescope located at the South Pole in the Antarctic. It has been under construction for the past 5 years and will be completed by the end of this year. The glacier ice is pure and deep at the South Pole. A perfect place to build a Neutrino detector. Perfect for the telescope; very harsh on the construction crew and the astronomers. The work can be done for only 3 months out of the year during the summer season. All the energy and supplies are flown in by military air craft. Diesel fuel is the only energy source. The telescope is constructed by drilling 80 holes into the ice using a drill bit of boiling water. The holes go down 2,450 meters into the ice.

- Next, a string of sensors are lowered down into each hole stretching from 1,450 meters to 2,450 meters deep. The matrix of 5,000 sensors forms a detector chamber in one cubic kilometer of pure ice. The detectors are photo multiplier tubes, with computers and transmission cables back to the surface. The photo multiplies are sensitive enough to detect a single photon. A series of detections might last 120 nanoseconds with each detector firing in sequence. The detections have a precision timing to within 2 nanoseconds. The light detection is from 400 to 800 nanometers wavelength. Instead of looking up into the sky the telescope looks down through the Earth. The Earth is used as a filter to stop random Cosmic Rays and to only detect Neutrinos that fly through the Earth unscathed. The Neutrinos fly into the block of ice. But, how does ICECUBE detect these neutrinos? And why do we call this a telescope? What can we learn from this particle detector?

- For a hundred years telescopes, like our eyes, were limited to visible light. We have made many discoveries using this part of the electromagnetic spectrum from 400 to 800 nanometer wavelengths. But, with modern instruments and satellites above the atmosphere we have begun discovering so much more. Telescopes now “see” infrared, X-rays, microwaves, Gamma rays and the full spectrum of electromagnetic radiation. Telescopes are hoping to use gravity waves and yes Neutrinos. All of these new instruments have resulted in and will result in new discoveries.

- Our Sun produces an abundance of Neutrinos. We hope to learn more about the Sun with this detector. Cosmic Rays hit our upper atmosphere and create a shower of Neutrinos. Nuclear Reactors produce Neutrinos. Dark Matter and anti-Dark matter annihilations could produce Neutrinos. Gamma Ray Bursters and Supernovae produce Neutrinos. A single Gamma Ray Burst lasting 1/10^th of a second can release more energy than the Sun will release over its 10 billion year lifetime. About 1,000 Gamma Ray Bursts occur each year. Some have been detected as far away as 12,400,000,000 lightyears. We hope to study all of these with the ICECUBE telescope. Where do Cosmic Rays come from? That has been a question unanswered for decades.

- Cosmic Rays are charged particles of hydrogen nuclei (protons) and atomic nuclei, ranging from helium up to iron nuclei. These particles are traveling near the speed of light when they enter our upper atmosphere and smash into gas molecules creating a shower of Muons and Neutrinos raining down on Earth’s surface. Because Cosmic Rays are charged particles they do not travel in a straight line. There is no way to tell what direction they are coming from. The source is the most powerful particle accelerator in the Universe, but what is it and how does it work. Cosmic Rays have energies up to 1,000,000,000,000 Giga electron volts. CERN particle accelerator will be at full power this year. It is the largest particle accelerator on Earth and its maximum power will be 14,000 Giga electron volts. Cosmic Rays are a million times more powerful.

- Neutrinos are neutral and unlike Cosmic Rays they do travel in straight lines. So, ICECUBE can detect the path of the neutrino and calculate where it came from. How does an neutrino get detected?

- The Neutrinos pass through the Earth and enter the cubic kilometer of pure ice. Trillions of neutrinos are doing this. Once in a while a Neutrino interacts with an electron and bumps it up into a high energy Muon. The Muon is a charged particle when it moves through the ice it creates a shockwave and the shockwave is traveling faster than light in the ice and radiating a cone of blue light called Cerenkov radiation. The flashes of blue light are detected by the photo multiplier sensors. Up to 10 sensors are triggered plotting a path through the matrix that can be recorded by the computer at the surface. Each year ICECUBE drilled more holes and added more sensors. To date they have detected 36,960 neutrinos and are busy plotting the paths backwards and studying the sources in the cosmos.

- What is Cerenkov radiation? The blue light was discovered by Pavel Alekseyevich Cerenkov in 1934. Light slows down in other medium such as water in inverse proportion to the medium index of refraction. The speed of light in air is 186,000 miles per second. The speed of light in water is 140,000 miles per second. When a charged particle enters a medium traveling faster than the speed of light in that medium it creates a shockwave. This is not unlike a sound shockwave created by a jet airplane. A wave front loud boom passes by you from the speeding jet overhead. The shockwave in the ice creates a cone of blue light in much the same way. The brightness, and the apex angle of the cone can be used to calculate the mass, charge, and velocity of the charged particle. The energy in the charged particle, a Muon in our case, is about 100 Giga electron volts.

- Nuclear reactors produce Cerenkov radiation. If you stand over a nuclear reactor core that is bathed in water you will see continuous flashes of blue light as Neutrinos are being emitted by the fusion reactions.

- When a traveling wave moves faster than the mediums wave speed a shockwave is produced. As all the traveling waves pile up on each other a tangential force is created. This in turn creates a “V” shaped cone shockwave. The cosine of the angle at the apex of the cone is equal to the ratio of the velocity of the wave to the velocity of the traveling wave. The 3 dimensional cone has only one wave front. The ratio of the velocity of the traveling wave to the medium wave is called the Mach Number. Jet planes use Mach numbers for sound waves. The larger the Mach Number the closer the apex angle is to 90 degrees. When we measure the angle of the Cerenkov blue light shockwave we can calculate the velocity of the Muon charged particle.

- ICECUBE can detect the Neutrinos coming from the Sun. It can even detect the shadow of the Moon as the Moon blocks some of the Neutrinos. In fact, that is how ICECUBE calibrates its angular resolution comparing its measurement to the angle to the Moon. A laser beam is used to calibrate the sensitivity of the detectors. There are 100 trillion neutrinos zipping through your body every few seconds. They reach you coming from the Sun in about 8 minutes. One inch of lead will stop an X-ray photon but it would take a lead slab on lightyear thick to stop a single neutrino. Fortunately there are trillions of them so in a large of detector some collisions are likely to happen.

- When Neutrino detectors were first used on average one hit a day was expected for a particular detector. However, this detector was getting one hit every 3 days. This confusion became known as the Solar Neutrino Problem. It was studied for decades before science realized there were 3 types of Neutrinos, Electron Neutrinos, Muon Neutrinos, and Tau Neutrinos. The nuclear reaction in the Sun only produces Electron Neutrinos. What was happening is that Neutrinos were changing types on their path to the Earth.

- When all 3 types were finally detected it matched the nuclear physics for the Sun perfectly. Proton + proton fusion into Deuterium ( 1proton, 1 neutron). Then, Deuterium + proton fusion into Helium-3 (2 protons, 1 neutron) . Then, Helium-3 + Helium-3 fusion into Helium 4 (2 protons, 2 neutrons) releasing 2 excess protons + Gamma rays, Positrons, and Neutrinos to carry off the excess energy. Helium has slightly less mass than 4 hydrogen masses, about 0.7% less. This excess mass is turned into energy according to E=mc^2. 98% of the excess energy is Kinetic Energy of radiation streaming out from the Sun. Neutrinos are carrying about 2% of this energy. The Sun is converting 4,000,000 tons of mass into energy every second.

- All the other stars and their Supernovae explosions also produce Neutrinos in nuclear fusion. Also electrons and protons fuse into neutrons in forming Neutron Stars and Blackholes. Gamma Ray Bursters, Blackhole collisions. Dark Matter and anti-matter collisions. Astronomer’s new Neutrino Telescope at the South Pole has a lot of targets to study. The data is pouring in. New discoveries are bound to occur. Stay tuned. There will be announcements shortly.

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(1) 11-1-10 lecture at SSU Kiril Filimonov UC Berkeley on ICECUBE Neutron Telescope in the Antarctica.
(2) To learn more from other Reviews on Neutrinos, #1139, #630, #732.
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707-536-3272, [email protected] Thursday, November 4, 2010