the nuclear reaction that creates neutrinos
Did
You Know...hundreds of billions of neutrinos pass through your body every
second?
Description
and Findings
Neutrinos are tiny, electrically neutral subatomic particles. Subatomic means they are one of the building blocks that makes up an atom. They are considered one of the fundamental particles, but are the least understood. Some recent experiments claim they have proved the neutrino has mass, but there is still not a general consensus. If it is proven they have mass, they would be the smallest particle with mass.
The
sun produces 200 trillion trillion trillion neutrinos, every second, and a
supernova blast can unleash 1000 times more neutrinos than the sun will produce
in its 10-billion year life.
The
Super-Kamiokande Collaboration includes scientists from 23 institutions in
countries including Japan and the United States, and is primarily funded by
the Japanese Ministry of Education, Science, Sports, and Culture (Mombusho).
Funding for the detector's outermost region is provided by the United States
Department of Energy. They announced at the "Neutrino '98" conference
that they had evidence of non-zero neutrino mass. They believe the muon-neutrinos
are oscillating, or changing into tau-neutrinos or perhaps some other type
of neutrino. Oscillation can only occur if the neutrino possesses mass.
There are three types, or flavors, of neutrinos: electron, muon, and tau, discovered in that order. Each type of neutrino is related to a charged particle, hence the names. The electron neutrino is related to the electron, and the muon- and tau-neutrinos are related to heavier versions of the electron known as the muon and the tau.
Neutrinos pass through almost everything on Earth, but scientists can use some detectors to find them. These detectors sometimes are based on the Cherenkov effect. The Cherenkov effect is based on the fact that nothing can travel faster than the speed of light in a vacuum. However, light travels slower in water, so other particles can travel faster in water. These detectors watch for neutrinos to interact with the highly purified water and create a flash, which is magnified by photomultiplier tubes (PMTs). The detector used by Super-Kamiokande Collaboration is located about 1000 meters underground in the Kamioka Mining and Smelting Company Mozumi Mine. SuperKamiokande can detect muon- and electron-neutrinos, and has a 50,000-ton water tank with over 13,000 photomultiplier tubes. The Sudbury Neutrino Observatory (SNO), which is a 12 meter sphere containing heavy water and is sensitive to all types of neutrinos. Heavy water is a form of water where there is a neutron in the hydrogen atoms. More information and locations for detectors can be found here.
The Sudbury Neutrino Detector (left) and SuperKamiokande (right)
The effect of neutrinos on other spatial bodies is not completely known, but two scientists (Henk Spruit and Sterl Phinney) have done thorough studies of pulsars and believe neutrinos may make them spin. The jet of neutrinos released during the collapse of the core shoots the pulsars across the galaxy at speeds of several hundred miles per second. They discovered if this outburst of neutrinos is focused slightly outside the pulsar's core, it would spin it just like a kicked soccer ball spins.
In physics, there is the
so-called problem of "missing mass". When scientists totaled up
all the mass, energy, and matter in some galaxies, the number wasn't high
enough to keep the galaxy from expanding, but it wasn't. Neutrinos are everywhere,
and if they have mass, they could be part of the "missing mass".
A Brief History of the Neutrino:
1931- Theorist Wolfgang Pauli predicted a hypothetical particle. Pauli based his theory on the fact that the starting amount of energy and momentum did not equal the ending total. He suggested this missing energy was being carried off by a neutral particle that was escaping detection.
1934- Enrico Fermi develops a comprehensive study of radioactive decays, the same method Pauli had used, and included Pauli's hypothetical particle. He coined the particle the neutrino, which is Italian for "little neutral one". When he includes the neutrino, Fermi's theory accurately explains many experimentally observed results.
1959- Discovery of a particle fitting the neutrino's expected characteristics is announced by Clyde Cowan and Fred Reines. Reines won the 1995 Nobel Prize for his contribution to this discovery. This neutrino is later recognized as the partner of the electron.
Fred Reines
1962- A new flavor of neutrino is during experiments at Brookhaven National Laboratory and CERN (the European Laboratory for Nuclear Physics). The researchers observed neutrinos produced in association with muons do not behave the same as electron-neutrinos. They name this new flavor of neutrino the muon-neutrino.
1968- The first experiment to detect electron-neutrinos produced by the sun reports less than half of the expected neutrinos are observed. The experiment used 615 tons of perchloro-ethylene in a old gold mine about 1.6 kilometers below the surface. This finding is the origin of the long-standing "solar neutrino problem". It is suggested that the missing neutrinos may have transformed into another type of neutrino undetectable in this experiment, but the unreliability of the solar model on which the expected rates are based is considered a more likely explanation.
Davis with his neutrino
detector
1978- The tau particle is discovered at SLAC (the Stanford Linear Accelerator Center). It is soon recognized as a heavier version of the muon and electron, and its decay exhibits the same apparent imbalance of energy and momentum that lead Pauli to predict the neutrino's existence in 1931. The existence of a third neutrino is hence inferred, but this neutrino has not been directly observed.
1985- The IMB (Irvine-Michigan-Brookhaven) experiment, at a large water detector that observes neutrinos as well as proton decay, notices there are fewer muon-neutrino interactions that expected. This anomaly is originally thought to be caused by detector inefficiencies.
1985- A Russian team reports the first measurement of a non-zero neutrino mass. The mass is extremely small (10,000 times less than the mass of an electron), but later attempts to reproduce the measurement are fruitless.
1987- Kamiokande, another large water detector tracking for proton decay, and IMB both detect a simultaneous burst of neutrinos from Supernova 1987A.
1988- Kamiokande, which is better able to distinguish muon neutrino interactions from those of the electron-neutrino, reports they have observed only about 60% of the expected muon-neutrino interactions.
1989- The Frejus and NUSEX experiments, which are much smaller than either Kamiokande or IMB and use iron rather than water, report no deficiency of muon-neutrino interactions.
1989- Experiments at CERN's Large Electron-Positron (LEP) accelerator determine there are no more flavors of neutrinos than the three that already exist.
SNO before the last panel of PMTs was installed
1989- Kamiokande confirms the long-standing anomaly of neutrinos from the sun by finding only 1/3 of the expected rate. It became the second experiment to detect neutrinos from the sun.
1990- Following an upgrade which improves the ability to identify muon-neutrino interactions, IMB confirms the deficiency of muon-neutrino interactions reported by Kamiokande.
1994- Kamiokande finds a deficiency of high-energy muon-neutrino interactions. Muon-neutrinos traveling the greatest distances from the point of production to the detector exhibit the greatest depletion.
1994- The IMB and Kamiokande groups collaborate to test the ability of water detectors to distinguish muon- and electron-neutrino interactions using a test beam at the KEK accelerator laboratory.
1996- The SuperKamiokande detector begins operation.
1997- The Soudan-II experiment becomes the first iron detector to observe the deficiency of moun-neutrinos. The deficit agrees with the findings of Kamiokande and IMB.
1997- SuperKamiokande reports a deficiency of cosmic-ray muon-neutrinos and solar electron-neutrinos at rates agreeing with previous findings.
1998-
The Super-Kamiokande Collaboration announces evidence of non-zero neutrino
mass at the "Neutrino '98" conference.
background courtesy of ESO
website by Barbara and Jesse