- The capital and chief port of Jamaica; pop. 538,000
- a town in southeast Ontario on Lake Ontario near the head of the Saint Lawrence River
- A port in southeastern Canada, on Lake Ontario, at the head of the St. Lawrence River; pop. 56,597
- A historic city in southeastern New York, on the Hudson River; pop. 23,095
- a town on the Hudson River in New York
- capital and largest city of Jamaica
- The devotion of time and attention to acquiring knowledge on an academic subject, esp. by means of books
- Activity of this type as pursued by one person
- analyze: consider in detail and subject to an analysis in order to discover essential features or meaning; “analyze a sonnet by Shakespeare”; “analyze the evidence in a criminal trial”; “analyze your real motives”
- An academic book or article on a particular topic
- survey: a detailed critical inspection
- applying the mind to learning and understanding a subject (especially by reading); “mastering a second language requires a lot of work”; “no schools offer graduate study in interior design”
- An empty area left between one-, two-, or three-dimensional points or objects
- A continuous area or expanse that is free, available, or unoccupied
- the unlimited expanse in which everything is located; “they tested his ability to locate objects in space”; “the boundless regions of the infinite”
- place at intervals; “Space the interviews so that you have some time between the different candidates”
- An area of land that is not occupied by buildings
- an empty area (usually bounded in some way between things); “the architect left space in front of the building”; “they stopped at an open space in the jungle”; “the space between his teeth”
171: Missing Neutrinos
The light that reaches us from the Sun takes only eight minutes or so to get to the Earth once it leaves the surface. However, those photons may have been produced millions of years ago in the centre of the Sun. There the photons will bounce around, be absorbed, emitted, reabsorbed and generally moved around with until they reach the surface. By the time they do so there’s virtually no information to be gleaned about their origin (though much to be learned about the top layers of the Sun). Photons are of no help, but there are other particles produced in the nuclear furnace deep within the Sun that do not interact much with the other matter around. These are neutrinos, and instead of taking millions of years to get out of the Sun they do it in minutes.
Neutrinos have no charge and so aren’t affected by electromagnetic fields. They fly straight and true and don’t interact much with matter either. Millions of neutrinos pass through our body every second, and indeed through the entire Earth. Rarely, very rarely, a neutrino will hit the nucleus of an atom and a reaction may occur. The neutrino detectors look for these rare events.
Deep within a mine, a huge tank of heavy water is surrounded by tens of thousands of photomultipliers, watching for incredibly faint flashes of light. When a particular type of neutrino hits the neutron in the centre of the Deuterium in the heavy water, the neutron is converted to a proton and the neutrino becomes an electron. This process emits light and can be detected!
However this process only detects Electron Neutrinos, and there are two other flavours of neutrino: Muon Neutrinos and Tauon Neutrinos. Until recently there was a problem. All the detectors around the world were picking up the light caused by Electron Neutrinos interacting with them. But there were far fewer Electron Neutrinos being detected than solar models predicted. These models fit very well with the results from observations of the photosphere and of helioseismology and so scientists were reluctant to throw them away. Could anything explain where the missing neutrinos were?
In a Canadian mine a new observatory was completed at the turn of the century. It was able to detect all flavours of neutrinos and soon discovered that the total number of neutrinos it observed was exactly in line with the number predicted by the solar models. There were less Electron Neutrinos but more of the other two flavours. Particles can change from one form to another, but for neutrinos to do so must mean that they have a rest mass of greater than zero. Unlike photons, these things do have a bit of weight to them!
And so every second the Sun pours forth its trillions of neutrinos, they shoot through the deep hot layers of the star and into space. Somewhere along the line many of them change flavour and then some of them pass straight through the Earth, while a tiny few others get slammed into some water where someone in a deep mine is watching for them. They interact with almost nothing in the universe, and yet we manage to observe them, with what purpose?
Why bother with Neutrinos? Neutrinos are tiny — really, really, tiny — particles of matter. They are so small, in fact, that they pass between, and even through, atoms without interacting at all. Neutrinos are everywhere: If we start counting now, more than 1 Quintillion (that’s 10^18 or one trillion billion) of them will have passed through our body by the time we finish this paragraph. Yet only one of those 1 Quintillion neutrinos will likely interact with an atom in our body. The rest will go merrily on their way! Staggering numbers of neutrinos constantly pass right through the earth and off into distant Space. Since they are so tiny, neutrinos were long thought to have no mass at all. In the last decade, however, neutrino oscillation experiments have definitively proved that neutrinos have masses, just extremely tiny ones!
The HQR image shows experiments at neutrino detectors like Super-K (Super-Kamiokande, Hida, Gifu Prefecture, Japan) and SNO (Sudbury Neutrino Observatory, Kingston, Ontario, Canada). Those experiments have established that neutrinos oscillate among various flavours, each with a different tiny mass. Neutrinos play an important role in particle physics, astrophysics and cosmology. Since neutrinos have no electric charge and have only weak interactions, they can travel much longer distances without being absorbed by matter or deflected by magnetic fields. So neutrinos can prov
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