3. Elusive Ghostly Neutrinos - ELUSIVE GHOSTLY NEUTRINOS M...

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Unformatted text preview: ELUSIVE GHOSTLY NEUTRINOS M. Ragheb 2/15/2007 INTRODUCTION At every second of time, hundreds of billions of neutrinos pass through each square inch of our bodies. They come from above us during the day and from below us at night when the sun is shining on the other side of the Earth. The neutrinos can reveal information about the sun, the nature of dark matter, and the large scale structure of the universe. The sun is a large neutrino factory, and the neutrinos that it produces proceed through matter without significant interaction: a single neutrinos out of 1011 passing through the whole Earth interacts with it. The sun releases 200 trillion trillion trillion or 2 x 1038 neutrinos every second in all directions. Cosmic neutrinos also reach us from a recently observed Black Hole at the center of our galaxy. Particle accelerators are used to produce terrestrial neutrinos. Neutron fission reactors also generate terrestrial antineutrinos in the radioactive decay of the fission products generated by the fission process. In fact they carry 5 percent of the fission energy produced. If the fission energy release per reaction is 200 MeV, the fission antineutrinos carry about 10 MeV. From that perspective nuclear fission reactors are beacons radiating antineutrinos to the rest of the Universe announcing the presence of humanity to possible observers as an intelligent civilization that has mastered the control of fission energy. They do emit a high flux rate of antineutrinos: 1021 antineutrinos/sec. The imbalance of matter and antimatter in the universe suggests a theory contending that its mass may have been produced from the decay of neutrinos and antineutrinos during the Big Bang. If that was the case, then they may have been the origin of everything around us and that we are descendants of the neutrinos. NEUTRINOS IN THE STANDARD MODEL According to the Standard Model of the constitution of matter, neutrinos are a type of lepton. Possessing no electrical or strong charge they almost never interact with any other particles. Most neutrinos pass right through the Earth without interaction. Neutrinos are produced in a variety of interactions, especially in particle decays. In fact, it was through a careful study of radioactive decays that physicists represented by Wolfgang Pauli hypothesized the neutrino's existence along the following line of reasoning: 1. In a neutron rich radioactive nucleus, a neutron at rest with zero momentum decays, releasing a proton and an electron. 2. Because of the law of conservation of momentum, the resulting products of the decay must have a total momentum of zero, which the observed proton and electron clearly do not. 3. Therefore, we need to infer the presence of another particle with appropriate momentum to balance the event. 4. An antineutrino is released carrying the energy. An example of such a reaction is the beta decay of the tritium isotope of hydrogen producing an antineutrino: * T 3 → 2 He3 + −1 e0 + ν e (1) 1 Because neutrinos were produced in great abundance in the early Universe and rarely interact with matter, there are a lot of them around. Their small mass, but the large energy that they carry, as well as their tremendous numbers may be contributing to the total mass of the universe and affecting its expansion. Neutrinos are leptons that ignore the electromagnetic and strong nuclear forces. Accordingly, they interact weakly with matter. They are of three families or flavors: the electron neutrino, produced from the decay of a positron, or in the form of an antineutrino with the decay of an electron, in the weak interaction force process of radioactive decay. The muon and tau families or flavors of neutrinos result from the decay events that produce muons and tau particles. The muon and tau are cosmic ray particles that are heavier than the electron. Quarks Matter constituents Fermions First generation Second generation Up Charm Third generation Top u t Down Strange Bottom d Leptons c s b Electron Muon e - µ - Tau τ- Electron neutrino Muon neutrino Tau neutrino νe νµ ντ Force carriers Bosons Photon Gluon γ g Bosons W+ W+ Z0 Fig. 1: The Standard Model matter constituents and charge carriers showing the electron, muon and tau neutrinos. Neutrinos from the supernova event SN 1987A reached the earth on February 23, 1987, at 11:19 pm, GMT, 6 hours before the light from the exploding star was seen. An article in American Scientist by M. A. Ruderman and A. H. Rosenfeld about neutrinos inspired the following scientific poem: COSMIC GALL, By John Updike Neutrinos, they are very small. They have no charge and have no mass And do not interact at all. The Earth is just a silly ball To them, through which they simply pass, Like dustmaids down a drafty hall Or photons through a sheet of glass. They snub the most exquisite gas, Ignore the most substantial wall, Cold-shoulder steel and sounding brass, Insult the stallion in his stall, And, scorning barriers of class, Infiltrate you and me! Like tall And painless guillotines, they fall Down through our heads into the grass. At night, they enter at Nepal And pierce the lover and his lass From underneath the bed –you call It wonderful; I call it crass DETECTION OF NEUTRINOS The detection of neutrinos can depend on the reversal of a reaction already known to occur between a proton and a negative muon, producing a neutron and a muon neutrino: 1 H 1 + µ − → 0 n1 + ν µ (2) Fig. 2: A high neutrino interaction in an aluminum spark chamber. Columbia University. The reverse reaction occurs when a neutrino interacts with a neutron leading to the generation of a proton and a negative muon. ν µ + 0 n1 → 1 H 1 + µ − (3) The neutrino itself cannot be seen, but the resulting negatively charged muon can be seen in a spark chamber. In this case a collection of parallel charged plates shows the path of the particle as a set of continuous discharges as the muon moves between them. Figure 2 shows a high neutrino interaction in an aluminum spark chamber at Columbia University. NEUTRINOS OCCURRENCE British astrophysicist Sir Arthur Eddington in 1920 proposed that the sun generates heat and light by fusing H into He. Every time four H nuclei fuse to become a single nucleus of He in the sun's core, an amount of mass is converted into energy. In 1930, the Austrian physicist Wolfgang Pauli conjured up the notion of a novel subatomic particle to solve a puzzle about the apparent non conservation of momentum in radioactive beta decays. A few years later, Italian physicist Enrico Fermi named the particle, which has no electrical charge, the neutrino, or “little neutral one.” At this time there was no conclusive evidence that the particle existed, and most scientists initially thought it may be impossible to ever detect it. Hans Bethe in 1939 in a paper: “Energy Production in Stars,” laid out details of how H is fused into He in stars like the Sun. His work lead to the understanding that the fusion process releases not only energy but also the particles whose presence Wolfgang Pauli conjectured. Each time four H nuclei fuse into a He nucleus, two neutrinos are emitted. In “Project Poltergeist” conducted at the Savannah River nuclear reactors site, Frederick Reines and Clyde Cowan built a neutrino detector and proved that the neutrino actually exists. THE SOLAR NEUTRINO PROBLEM Scientists believe they understand the thermonuclear reactions occurring at the center of the sun, they know the temperature of its core, which dictates the reaction rate, and consequently know the rate at which the solar neutrinos should be emitted. The problem was that the existing theories predicted twice the number of solar neutrinos actually detected on Earth. The proton-proton fusion reaction: 1 H 1 + 1 H 1 → 1 D 2 + +1 e0 + ν e (4) is presumed to dominate the sun’s energy production process. The released “pp neutrinos” are thought to account for more than 90 percent of the neutrino flux from the sun. Several experiments had been set up for their detection. These experiments were aimed at resolving the “solar neutrino problem.” The standard solar neutrino model predicted that gallium detectors should see solar neutrinos at the rate of: 132 ± 7 SNU where: 1 SNU = 1 Solar Neutrino Unit = one neutrino capture per second for every 1036 atoms of relevant target isotopic species of the detector from the reaction: ν e + 31 Ga 71 → 32 Ge71 + −1 e0 (5) After 295 days of exposure, the Gallex experiment collaboration reported a neutrino capture rate of: 63 ± 16 percent, or about half of that predicted by the standard solar model. Efforts were made to explain the discrepancy, by lowering the temperature estimates of the sun's core: the cool sun theories. Unfortunately that could not explain the luminosity of the sun. If the Gallex and Sage experiments were discovering a severe dearth of solar neutrinos, that was suggesting the presence of: 1. Something quite new about the sun. 2. Something new about neutrinos. An explanation based on quantum mechanics is that the neutrinos oscillate, where one sort of neutrinos turns into another. For instance, one can think about electron neutrinos turning into muon neutrinos. The detectors would be detecting the electron neutrinos, but not the muon neutrinos. Results from the Sudbury Neutrino Observatory (SNO) eventually suggested the detection of neutrinos of different flavors: electron neutrinos from the sun, muonneutrinos, and tau-neutrinos. The results suggested that the electron neutrinos actually change into other families or flavors on their long trip from the sun’s interior. This explained the mystery of the missing solar neutrinos. HOMESTAKE BROOKHAVEN NATIONAL LABORATORY, BNL EXPERIMENT, USA Ray Davis as an experimentalist and John Bahcall as a theoretician proposed in 1964 at the Brookhaven National Laboratory (BNL) that a study of neutrinos emitted from the sun could check a theoretical model of nuclear fusion in its core. John Bahcall had created a detailed mathematical model of fusion reactions in the sun's interior. He took into account a variety of nuclear reactions at energies where measurements were difficult. He drew upon Hans Bethe's earlier work, including his estimate of the sun's core temperature. According to the model, the flux of solar neutrinos on Earth would be 1013 solar neutrinos/(cm2.second). At the bottom of the Homestake gold mine in Lead, South Dakota, sheltered from the confusing background cosmic radiation, Ray Davis oversaw the construction of a giant neutrino detector: a tank of cleaning fluid roughly as large as an Olympic size swimming pool. The cleaning fluid contained mostly Cl, which occasionally turns into a radioactive isotope of Ar gas when struck by solar neutrinos. John Bahcall had calculated that roughly 10 atoms of radioactive Ar will be produced each week, and Ray Davis was confident he could extract and measure them. As of 1968, the Homestake experiment had detected only about 1/3 as many radioactive Ar nuclei as predicted by the theoretical model. Other scientists called the discrepancy “The Solar Neutrino Problem,” and a “Social embarrassment.” The popular press called it “The Mystery of the Missing Neutrinos.” In the two following decades after their disappointing results, Ray Davis finetuned his solar neutrino detector, and John Bahcall refined and checked his calculations. Hundreds of other physicists, chemists, and astronomers also examined the work, but no one could find significant fault with either the apparatus or the calculations. NEUTRINO OSCILLATIONS Russian physicists Vladimir Gribov and Bruno Pontecorvo, suggested that Ray Davis and John Bahcall's missing solar neutrinos can be explained by a phenomenon of “neutrino oscillations”: as they travel to Earth, some of the neutrinos made inside the sun oscillate, or change, into types of neutrinos that Davis's apparatus could not detect. It was known since the mid century that different types of neutrinos existed: electron neutrinos νe, muon neutrinos νµ , and tau neutrinos ντ. Initially, few physicists gave credence to Vladimir Gribov and Bruno Pontecorvo's idea. According to the Standard Model, the cornerstone of modern particle physics, neutrino types are distinct and can never change one into another, since they were thought to be massless and traveling at the speed of light, hence time was frozen for them. Based on Gribov and Pontecorvo's suggestion, Lincoln Wolfenstein in 1978 and Stanislav Mikheyev and Alexei Smirnov in 1985 showed how electron neutrinos created at the sun's core might switch their quantum states from electron neutrinos νe, to muon neutrinos νµ, and tau neutrinos ντ. as they interacted with other matter in the sun and traveled outward to its surface. If neutrinos change flavor, according to quantum theory, then they must possess a mass. If they possess a mass then there is something that needs to be modified in the standard model of particle physics. This is a vast field for theoreticians to describe a Universe that is getting more and more interesting to describe and study. Regardless, it has inspired another neutrino poem written for those interested in the mystery of the solar neutrinos and the measurement of the Solar Neutrinos Units (SNUs): STALKING SOLAR NEUTRINOS, By Barbara Goss Levi In caverns deep under the ground They hunt SNUs like hungry bloodhounds. But maybe the prey Can change ‘long the way And sneak by without being found. Who would have thought that they could change their flavors while travelling from the Sun to the Earth? ATMOSPHERIC NEUTRINO ANOMALY, THE KAMIOKANDE EXPERIMENT, JAPAN In 1985, using an experiment called Kamiokande, sited in the Kamioka Mozumi mine in Japan, Masatoshi Koshiba and his colleagues detected far fewer atmospheric neutrinos or neutrinos produced by the collision of cosmic rays with the Earth's atmosphere than they expected to see. While atmospheric neutrinos are a different type from the electron neutrinos produced by the sun, the so called “Atmospheric neutrino anomaly” was similar to the solar electron neutrino problem. SUPER KAMIOKANDE EXPERIMENT, JAPAN A scaled-up version of the Kamiokande experiment called Super Kamiokande reported in 1998 on more than 500 days of data collection. The detector was so large that it could tell what direction atmospheric cosmic ray neutrinos were coming from, and it picked up far fewer neutrinos traveling from the other side of the Earth than from the sky directly above it. There was evidence that many of the atmospheric neutrinos from the other side of the Earth have changed into a different type of neutrino during their journey across the Earth. This confirmation of neutrino oscillations carried a profound implication: the Standard Model of particle physics had to be modified, suggesting that neutrinos did not travel at the speed of light, that they had a time frame, could change their flavor, and consequently possessed a mass. SUDBURY NEUTRINO OBSERVATORY, SNO EXPERIMENT, CANADA This experiment was located in Ontario, Canada and consisted of a 40 feet diameter sphere filled with Heavy Water, D2O, buried 6,800 feet or 2,000 meters underground in a Nickel mine cavity the size of a ten story high building in Ontario, Canada. The 40 feet wide tank is surrounded by photo multiplier tubes to detect the Cerenkov radiation emitted by neutrinos interacting with the deuterium in 1,100 tons of heavy water, D2O. The location deep underground shields it from cosmic radiation from space that would interfere with its detection of the neutrinos. About 20 times each day, a neutrino interacts with a neutron in the heavy water and releases a faint flash which is detected by the 9,600 photo multiplier tubes around the tank, and then analyzed for data about the neutrino that caused it. In 2001-2002, the Sudbury Neutrino Observatory (SNO), the first neutrino detector that can pick up all three known types of neutrinos, resolved conclusively that, in the case of the missing solar neutrinos, the neutrinos are not, in fact, missing. SNO found that the total number of neutrinos from the sun is remarkably close to what John Bahcall predicted three decades earlier. Ray Davis's experimental work was vindicated as well, because SNO found that only about 1/3 of the solar neutrinos that reached the Earth were still in the same state of electron neutrinos that Ray Davis could measure in the Homestake mine experiment, while 2/3 of them changed their type, flavor or oscillated during their journey. NOBEL PRIZE AWARD The Nobel Prize in Physics in 2002 was awarded to Ray Davis in the USA and Masatoshi Koshiba, the leader of the Kamiokande group in Japan. The Nobel Committee citation praised them “For pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos.” The award was a tribute to their colleagues and the many dedicated scientists whose work led to a fundamental shift in particle physics. NEUTRINO DETECTION EXPERIMENTS COWAN AND REINES EXPERIMENT The ingenious experiment by Cowan and Reines at Hanford, Washington, depended on the reaction between an antineutrino from the beta decay of the fission products in a fission reactor and a proton creating a neutron and a positron: ν e + 1 H 1 → 0 n1 + +1 e0 * (6) The positron meets its antiparticle the electron in the body of a detector containing H2O and cadmium to absorb the emitted neutrons. The positron meets an electron, which is its antiparticle. The result is a matter-antimatter annihilation process in which the mass of the positron and the mass of the positron are totally converted into electromagnetic radiation in the form of two gamma ray photons: +1 e 0 + −1 e 0 → γ + γ (7) These gamma photons are detected by surrounding scintillation detectors after a 10-9 second time delay. The cadmium in the water next absorbs the emitted neutron, in turn emitting gamma photons, but after a time delay of 10-5 second. 0 n1 + 48 Cd114 → 48 Cd115 +γ (8) The coincidence detection of these two events by the scintillation detector implies a neutrino detection. Fig. 3: The scintillation counter in the Reines and Cowan experiment for neutrinos detection. The scintillation counter is the cylindrical object at the bottom of the figure. THE GALLEX SOLAR NEUTRINO EXPERIMENT The GALLEX (GALLium EXperiment) detector contained 30 tons of Gallium, and sat in a tunnel in a laboratory underneath the Gran Sasso d’Italia, a 2,900 meter high peak in the Appennine mountains, where movie actor Sylvester Stallone’s “Cliff Hanger” movie was filmed, northeast of Rome. THE SAGE EXPERIMENT The SAGE (Soviet American Gallium Experiment) was a Gallium experiment, located at the Baksan Neutrino Observatory under Mt. Andyrchi in the Caucasus, and operated with 57 tons of gallium. THE LAKE BAIKAL EXPERIMENT This experiment was conducted at the bottom of Russia’s frigid Lake Baikal. The thickness of the lake’s water absorbed cosmic particles, but neutrinos were able to penetrate it. HOMESTAKE GOLD MINE EXPERIMENT This experiment, now ended, was the first to detect solar neutrinos in the early 1970s. The Homestake detector, pioneered by Nobel laureate in physics Raymond Davis Jr., consisted of a tank of 615 tons of perchloro-ethylene, a dry cleaning fluid, surrounded by another ordinary water tank. The tank was situated in the Homestake gold mine in Lead, South Dakota. About twice every three days, a neutrino would interact with a nucleus of chlorine in the liquid and produce a nucleus of radioactive argon. Raymond Davis developed techniques to extract the few atoms of radioactive argon created each month by flushing them with He gas, and count their radioactivity. He observed about 1/3 of the expected solar neutrinos. This led to the famous “Solar Neutrino Problem,” which was resolved in 2001-2002 by the Sudbury Neutrino Observatory (SNO) experiment in Canada. The experiment involved the Brookhaven National laboratory (BNL) solar neutrino detector. It was composed of a tank 20 feet in diameter and 48 feet in length containing 10,000 gallons of perchloro-ethylene, a dry-cleaning fluid containing substantial amounts of chlorine. It was located 4,850 feet underground at Lead, South Dakota’s Homestake gold mine for a duration of 20 years. The underground location was meant to minimize the noise caused by cosmic rays, which are stopped by the overlaying rock. This detector was designed to observe the solar neutrino flux by the capture of neutrinos to form radioactive argon by the reaction with the chlorine in perchloroethylene: ν e + 17 Cl37 → 18 Ar 37 + -1 e0 (9) Every 2 months, the quantity of argon indicated the number of neutrinos collisions, which was extrapolated to the total number of neutrinos passing through the tank. Fig. 4: The Homestake gold mine solar neutrino experiment in South Dakota, USA. KAMIOKA LIQUID SCINTILLATOR ANTINEUTRINO DETECTOR, KAMLAND DETECTOR An international team of physicists completed construction on the KAMLAND detector in 1997 on the Japanese island of Honshu. This experiment targeted antineutrinos, the antimatter opposites of neutrinos, which signal the latter's presence. The detector used a telescope made of 1,000 tonnes of mineral oil and benzene in a stainless steel tank two thirds of a mile below the Earth's surface to measure antineutrinos issuing from nuclear power reactors and natural nuclear reactions such as the decay of the K40, Th232 and uranium radioactive isotopes in the Earth’s core and mantle. In July 2005, KAMLAND scientists measured the Earth's total radioactivity for the first time. Their findings will allow them to better understand what keeps the planet warm, the volcanic activity, the continental drift, the Earth’s magnetic field churning and the core dynamo: phenomena that enable life on Earth. Until this discovery, geologists relied on earthquakes’ seismic data to estimate the planet's radioactivity. Fig. 5: The KAMLAND antineutrino detector. Honshu island, Japan. Fig. 6: Cerenkóv radiation emitted by electrons moving in water of a pool type research fission reactor. THE MiniBooNE EXPERIMENT AT FERMILAB This experiment at the Fermi National Accelerator Laboratory, Fermilab, in Batavia, Illinois, investigates the oscillation of neutrinos from one type to another. Since 2003, it has observed neutrinos created from protons in Fermilab's particle booster, part of the system that the laboratory normally employs to accelerate protons to higher energies for other experiments. MiniBooNE is a 40 feet diameter spherical steel tank filled with 800 tons of mineral oil and lined with 1,280 phototubes that produce a flash of Cerenkóv light when charged particles travel through them. Analysis of these Cerenkóv radiation flashes are providing information about the nonzero status of the neutrino mass. Fig. 7: Phototubes being adjusted in the MiniBooNE experiment at Fermi Lab, Batavia, Illinois. MAIN INJECTOR NEUTRINO OSCILLATION SEARCH, MINOS DETECTORS MINOS is a two detector experiment at Fermilab that began studying neutrino oscillations in 2003. It uses a beam of neutrinos that first pass through a detector at Fermilab and then through another detector hundreds of miles away deep within the Soudan Iron Mine in northern Minnesota. The distance between the two detectors maximizes the probability that the neutrinos will have revealing interactions over the course of their journey. An international collaboration of particle physicists at Fermilab uses MINOS to investigate the puzzle of neutrino mass. The 98 feet long detector consists of 486 massive octagonal planes, lined up like the slices of a loaf of bread. Each plane is made of a sheet of steel covered on one side with a layer of plastic that emits light when struck by a charged particle. MINOS is meant to help researchers answer some of the fundamental questions of particle physics, such as how particles acquire mass. Fig. 8: Inside of MINOS detector setup at Fermilab. THE SUPER KAMIOKANDE EXPERIMENT This detector began operating in 1996, half a mile underground in a zinc mine in Kamioka, Japan. Japanese and American scientists erected a huge tank of water 138 feet tall to hunt for neutrinos. The walls, ceiling, and floor of the 12.5 million gallons tank were lined with 11,242 light sensitive phototubes. These picked up and measured bluish streaks of light in the form of Cerenkóv radiation, which is left behind as neutrinos travel through the water. Super Kamiokande detected neutrinos that nuclear interactions in the sun and the cosmic rays interactions in the Earth’s atmosphere produce. In 2001, after several promising discoveries related to potential neutrino mass, the Super Kamiokande was crippled when several thousand of its light detectors exploded and were repaired. The experiment started operation in 1996 and contained 50,000 tons of ultra pure water. By 1998 the experiment had gathered sufficient evidence of neutrino oscillations, which is the metamorphosis of one neutrinos subspecies or flavor into another. Starting 1999, man-made neutrinos pulses that were generated 250 kilometers away at the KEK particle accelerator in Tsukuba, were directed towards it. The 11,000 photo multiplier tubes meant to detect solar neutrinos could more easily detect those from the KEK to Kamioka or K2K experiment. Over two and a half years, Super-K detected 56 K2K neutrinos, compared with 81 expected in the absence of neutrinos oscillations. This suggested new physics; implying that on the way to Kamioka one third of the neutrinos oscillate to a flavor that Super-K could not detect. A new experiment was planned designated as JHF-Kamioka. This would sent a 10 times more intense neutrino beam from a new accelerator being built at Tokaimura, 300 kilometers away. Long range plans call for the construction of Hyper-Kamiokande which would contain 20 times the water content of Super-K at 1 megaton of pure water. Fig. 9: The Super Kamiokande array of detectors, Japan being inpected by technicians in inflatable boats. THE SUDBURY NEUTRINO OBSERVATORY, SNO The Sudbury Neutrino Observatory (SNO) is a collaborative effort among physicists from Canada, the UK, and the USA Using 1,100 tons of heavy water D2O and almost 10,000 photo multiplier tubes detectors. These measure the flux, energy, and direction of solar neutrinos, which originate in the sun. SNO, located 6,800 feet underground in an active Ontario nickel mine, can also detect the other two types of neutrinos, muon neutrinos and tau neutrinos. In 2001, just two years after the observatory opened, physicists at SNO solved the mystery of the “missing solar neutrinos.” They found that the answer does not originate with the sun, where many physicists had suspected that solar neutrinos undergo changes, but with the journey they take from the core of the sun to the Earth where they undergo oscillations changing their flavors from one type of neutrino to another. … Fig. 10: Overall view of the Sudbury Neutrino Observatory, SNO, Canada. COSMIC NEUTRINOS: THE ANTARCTIC MUON AND NEUTRINO DETECTOR ARRAY, AMANDA Researchers from the USA, Belgium, Germany, Sweden have been trying to observe the most energetic astronomical phenomena and objects that cannot be seen with ordinary telescopes by observing neutrinos and muons. The instrument used is the Antarctic Muon And Neutrino Detector Array (AMANDA). Three stages of the experiment are shown in the figure: Amanda-A with 4 strings of instruments, Amanda-B with 10 strings, and Amanda II with 3 strings measuring the characteristics of ice above it and 6 strings forming a cylinder around Amanda-B. Fig. 11: The Antarctic Muon And Neutrino Detector Array (AMANDA) under ice. The experiment is housed in holes in Antarctic ice, drilled by injecting hot water into the ice. It consists of arrays of optical modules containing photo multiplier tubes strung on vertical cables within an imaginary cylinder 200 m in diameter and 500 m high buried beneath 2 km of ice. The objective is not the solar neutrinos, but the cosmic neutrinos emitted by colliding black holes, exploding stars or supernovae, gamma ray bursts, and other energetic cosmic phenomena. These cosmic neutrinos are 105 times more energetic than solar neutrinos, and -12 also 10 times rarer in occurrence. This requires a large size detector to detect them. One needs weakly interacting particles like neutrinos to see the rest of the Universe, since photons of comparable energy cannot reach Earth from beyond the Milky Way galaxy, being mostly absorbed by interactions with photons left over from the postulated Big Bang event. The flux of these high-energy neutrinos is smaller at higher energies necessitating large detectors. The detection depends on the inverse reaction where a neutrino interacts with a neutron producing a proton and negative muon described earlier. In this case the detection process attempts at detecting the blue Cerenkóv radiation emitted by the muon as it moves through the ice at faster than the speed of light in ice. The photo-multiplier tubes are meant to detect and amplify the Cerenkóv radiation by a factor of 108 times. The light is turned into electrical pulses to be recorded by electronic counters. By studying the track of the muon, the energy of the original particle can be inferred, as well as the direction that it came from. One hopes to identify consequently its source. From this perspective, it becomes a new kind of telescopic instrument. Antarctica is an inhospitable place to build and operate a telescope. But crystalclear ice is an excellent medium for observing neutrinos as they pass through the Earth. Since 1999, AMANDA, has used the Antarctic ice to seek out neutrinos. When the particles interact in the ice they can produce muons, charged particles that are like electrons but heavier. The muons create faint flashes of light as they pass through the ice some 1.2 miles below the surface, where they are sensed by AMANDA's hundreds of light sensitive phototubes supported on 19 tethers frozen in the ice. AMANDA's goal is to conduct neutrino astronomy, identifying and characterizing extra solar sources of neutrinos, which could provide important clues in the search for dark matter. Fig. 12: Holes drilling for the AMANDA Experiment, Antarctica. ICE CUBE INTERNATIONAL NEUTRINO EXPERIMENT An event occurred in 1998, where Amanda tracked a neutrino 400 meters through the ice. This was the highest energy neutrino ever recorded, but was not tied to any extra galactic source. To do the intended job, its size would have to be extended 10 times to a 1 cubic kilometer. This detector is named: IceCube, and will have 5,000 optical modules. The hope is to learn about new phenomena that photon telescopes cannot deal with. For instance the enigmatic gamma ray bursts are believed to emit neutrinos after the electromagnetic radiation has occurred. This could also shed light on another mystery concerned with the origin of high-energy cosmic rays, which may prove to be two aspects of a single phenomenon. When completed in 2009, IceCube, an international neutrino experiment involving more than 20 research institutions, will become the largest particle detector ever built. Setting IceCube's 4,200 optical modules deep within the Antarctic ice, where the detector joins its predecessor, AMANDA, will require drilling 70 holes a mile and a half deep each using a novel hot water drill. The detector's goal will be to investigate the still mysterious sources of cosmic rays. IceCube's telescope will use the Antarctic ice to look for the signatures of cosmic neutrinos, elusive particles produced in violent cosmic events such as colliding galaxies, black holes, quasars, and other phenomena occurring at the margins of the Universe. Fig. 13: IceCube hot water drilling in Antarctica’s ice. ASTRONOMY WITH A NEUTRINO TELESCOPE AND ABYSS ENVIRONMENTAL RESEARCH, THE ANTARES EXPERIMENT The Amanda ice experiment is supplemented by an experiment attempting to detect Cerenkov radiation in water under sea in the Mediterranean. The Astronomy Neutrino Telescope Abyss Research (ANTARES) is secured 2,330 meters under water off the coast of Toulon, France, and a separate string near Marseilles. It was initially planned as consisting of 13 strings of optical modules within an area 300 meters in diameter. Later, it would be expanded into a cubic kilometer array. The Amanda and Antares experiments will complement each other. But to have a full coverage of the sky, some initiative is needed to build a similar experiment in the southern hemisphere. The aim of this experiment is to answer questions about the composition of deep space by detecting neutrinos on the sea floor. ANTARES would start operation in 2006 and will use water 8,200 feet below the surface of the Mediterranean off the south coast of France to detect muons which are produced when neutrinos from space interact in the Earth's core. Muons create Cerenkov radiation as they pass through water, and an array of approximately 1,000 photomultiplier tubes on 10 vertical strings spread over a mile and a half of seafloor would sense and measure them. Fig. 14: Installation of the ANTARES experiment in the Mediterranean. ANITA NEUTRINO DETECTOR, ANTARCTICA If successful, the ambitious and innovative ANITA neutrino detector will be the first device to identify high energy neutrinos created by collisions between cosmic rays and cosmic microwave photons in space. Studying neutrinos from these sources offers an opportunity to learn about exotic objects at the edge of the universe, such as the black holes. Fig. 15: Balloon carrying the ANITA neutrino detector. Beginning in 2006, ANITA will be a balloon borne radio detector experiment circling the Antarctic continent at 115,000 feet during approximately 18 day missions. It will scan the vast expanses of ice for telltale pulses of radio emission generated by neutrino interactions. ANNIHILATION OF MUON NEUTRINOS AND ANTINEUTRINOS INTO ELECTRON-POSITRON PAIRS According to V. A. Gusseinov, various processes of inelastic scattering of cosmic neutrinos and antineutrinos of ultra high energy on low energy relic antineutrinos and neutrinos in the Milky Way Galaxy can be considered as a possible source of cosmic ray electrons and positrons of high energy through the process: * ν µ + ν µ → e+ + e− (10) The channel of the reaction is thought to arise at the expense of quantum effects. For the strong magnetic field case the cross section of the process does not depend on the masses of the charged leptons. The contribution of the weak external field to the cross section of the process is very small. ANTINEUTRINOS MONITORING OF FISSION REACTORS Antineutrinos result from the beta decay of the fission products and carry about five percent of the energy of the fission process. They can be used to monitor the fission process in fission reactors in real time. The International Atomic Energy Agency IAEA) considers 8 kgs of Pu239 to be a proliferation concern, and needs to monitor about 400 civilian reactors worldwide. In fission of the isotopes U235 and Pu239 result in the creation of antineutrinos possessing different properties allowing the measurement of the ratios of the two isotopes in a fission reactor. Over a broad range of antineutrino energies the number emitted by Pu239 is substantially less from the number emitted by U235 over a particular energy range. As Pu239 is bred from U238 and builds up in the fuel, the antineutrino count rate is observed to drop by 5-10 percent over the fuel cycle lifetime. Fission reactors emit a high flux rate of antineutrinos of 1021 antineutrinos/sec, which compensated for their low interaction probability, and allowing their detection. A method to detect antineutrinos can depend on coherent scattering from the nuclei. In this case, an antineutrino passing close to a nucleus causes it to shake and shed a few electrons in the process. Another possible detection mechanism is the inverse beta decay process, where an antineutrino interacts with a free proton in the detector creating neutron and a positron. The positron provides a measurable signature through the coincidence counting of the two gamma photons emitted by the annihilation process with an electron from Eqns. 6 and 7; essentially the same process used for their detection by Reines and Cowan: ν e + 1 H 1 → 0 n1 + +1 e0 * +1 e 0 + −1 e 0 → γ + γ A detector would consist of three subsystems: 1. Central detector: is where the antineutrino are detected consisting of stainless steel cells filled of a liquid scintillator. The scintillator contains quasi-free electrons and is doped with gadolinium atoms. The antineutron interaction with the proton creates a positron which soaks its energy converting it into a flash of electromagnetic radiation and induces a scintillation in the scintillator liquid. Another flash of light is emitted a nanosecond later by the positron annihilation with an electron producing 2 gamma photons. A third flash is emitted 30 microseconds later by the neutron absorption by a gadolinium nucleus, reaching an excited state and then being de-excited by the emission of a high energy gamma photon. The three consecutive flashes of light are detected by photomultiplier tubes situated above the scintillation fluid and constitute a signature of an antineutrino interaction. 2. Passive water shield: surrounds on all sides the central detector. It attenuates the gamma and neutron backgrounds. 3. Active water shield: is placed outside the passive shield and detects the penetrating cosmic rays signals which can mimic the antineutrinos and vetoes them out. Two methods can be used to track the Pu239 and U235 ratio in a fission reactor. The first method depends on a correlation designated as the burnup effect, and measures the changes in the total rate of detected antineutrinos over time. Since the Pu239 produces less antineutrinos than U235, the change in the antineutrinos rate tracks the production of Pu239 over time. If the antineutrinos count rate is 1,000 per day and decreases to 900 per day, and if the Pu is removed along the way or its production is increased, the changes will appear in the antineutrino count rate. This requires the simultaneous measurement of the reactor power level; otherwise a reduction in the antineutrino count can be masked by an increase in the reactor’s power. The second method considers changes in the antineutrinos energy spectrum, and does not need a measurement of the reactor power level, even thogh it needs a longer counting time to achieve an acceptable statistical error. It depends on the different energy spectra of the antineutrinos emitted by Pu239 and U235 and measures the ratios between the low and high ends parts of the spectrum. Such detectors can be placed outside the reactor’s containment and would be independent of the power production process. Since 2003, a 2x3 m prototype placed 17 m below ground and 25 m away from the reactor core, has been operational at the San Onofre plant in San Clemente, California. ANTINEUTRINO SETI BEACON PROPOSAL Nuclear fission reactors are a beacon radiating antineutrinos to the rest of the Universe announcing humanity as an intelligent civilization that has mastered the control of fission energy. By dedicating a nuclear reactor to ramping and operation at specific power levels, humanity can construct a beacon communicating with any possible existing other technological civilizations. With a programmed ramping of the fission reactor, these technological civilizations would quickly realize the non random nature of the emissions. By teaching them how to interpret subsequent messages, a language can be taught to them. Once a language is taught, the text of an Encyclopedia could be transmitted. This would constitute a mirror image of the Search for Extra Terrestrial Intelligence (SETI) project. In fact by announcing its presence, humanity may well receive a programmed response instead of looking for the signature of a message that may have never been sent. REFERENCES 1. 2. 3. 4. 5. 6. Ann Parker, “Monitoring Nuclear Reactors with Antineutrinos,” Science and Technology Review, pp. 21-23, January/ February 2006. Fred Hoyle, Jayant Narlikar, and John Faulkner, "The Physics-Astronomy Frontier," W. H. Freeman and Company, San Fransisco, 1980. Gerhart Friedlander, Joseph W. Kennedy and Julian Malcolm Miller, "Nuclear and Radiochemistry," John Wiley and Sons, Inc., New York, 1966. S. Nadis, "Hunting the Invisible," Popular Science, April, 2001. G. P Collins, “Setback for Super-K,” Scientific American, p.26, Feb. 2002. V.A. Gusseinov, “Annihilation of a muon neutrino and antineutrino into an electron-positron pair in an electromagnetic field.” Academic Open Internet Journal, Vol. 4, 2001. ...
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This note was uploaded on 06/16/2010 for the course NPRE 402 taught by Professor Ragheb during the Spring '08 term at University of Illinois at Urbana–Champaign.

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