Neutrino. Bei Wechselwirkung der Neutrinos mit Materie finden, anders als bei den anderen bekannten Elementarteilchen, nur Prozesse der schwachen Wechselwirkung statt. Reaktionen erfolgen im Vergleich zur elektromagnetischen und starken Wechselwirkung also relativ selten. Ein einzelnes Ereignis - wenn es eintritt - kann dennoch große Energiemengen freisetzen. Ein Strahl von Neutrinos geht auch durch große Schichtdicken – z. B. durch die ganze Erde – fast ungeschwächt hindurch. Forschungsgeschichte[Bearbeiten] Pauli schlug in einem Brief vom 4. Die erste Aufnahme eines Neutrinos in einer Blasenkammer gefüllt mit flüssigem Wasserstoff am Argonne National Laboratory von 1970.
Oberes Bild (gespiegelt und anderer Kontrast) mit eingezeichneten Spuren: Zu sehen ist die Reaktion . ) von unten links kommend (unsichtbar) kollidiert mit einem Proton (p) des flüssigen Wasserstoffs. ) und ein negativ geladenes Myon ( Pauli nahm an, dass das Neutrino nur äußerst schwer nachweisbar sei. Eigenschaften[Bearbeiten] Solar neutrino problem. The solar neutrino problem was a major discrepancy between measurements of the numbers of neutrinos flowing through the Earth and theoretical models of the solar interior, lasting from the mid-1960s to about 2002. The discrepancy has since been resolved by new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics – specifically, neutrino oscillation.
Essentially, as neutrinos have mass, they can change from the type that had been expected to be produced in the Sun's interior into two types that would not be caught by the detectors in use at the time. Introduction[edit] The Sun is a natural nuclear fusion reactor, powered by a proton–proton chain reaction which converts four hydrogen nuclei (protons) into alpha particles, neutrinos, positrons and energy.
Measurements[edit] In the late 1960s, Ray Davis's and John N. Proposed solutions[edit] Changes to the solar model[edit] Resolution[edit] See also[edit] References[edit] External links[edit] Electron neutrino. Proposal[edit] In the early 1900s, theories predicted that the electrons resulting from beta decay should have been emitted at a specific energy. However, in 1914, James Chadwick showed that electrons were instead emitted in a continuous spectrum.[1] n0 → p+ + e− The early understanding of beta decay In 1930, Wolfgang Pauli theorized that an undetected particle was carrying away the observed difference between the energy, momentum, and angular momentum of the initial and final particles. n0 → p+ + e− + ν0 e Pauli's version of beta decay Pauli's letter[edit] On 4 December 1930, Pauli wrote a letter to the Physical Institute of the Federal Institute of Technology, Zürich, in which he proposed the electron neutrino as a potential solution to solve the problem of the continuous beta decay spectrum.
A translated reprint of the full letter can be found in the September 1978 issue of Physics Today.[3] Discovery[edit] Name[edit] Pauli originally named his proposed light particle a neutron. Notes[edit] Neutrino oscillation. Observations[edit] A great deal of evidence for neutrino oscillation has been collected from many sources, over a wide range of neutrino energies and with many different detector technologies.[2] Solar neutrino oscillation[edit] The first experiment that detected the effects of neutrino oscillation was Ray Davis's Homestake Experiment in the late 1960s, in which he observed a deficit in the flux of solar neutrinos with respect to the prediction of the Standard Solar Model, using a chlorine-based detector. This gave rise to the Solar neutrino problem.
Many subsequent radiochemical and water Cherenkov detectors confirmed the deficit, but neutrino oscillation was not conclusively identified as the source of the deficit until the Sudbury Neutrino Observatory provided clear evidence of neutrino flavor change in 2001. Solar neutrinos have energies below 20 MeV and travel one astronomical unit between the source in the Sun and detector on the Earth. Atmospheric neutrino oscillation[edit] where . . SN 1987A. A time sequence of Hubble Space Telescope images, taken in the 15 years from 1994 to 2009, showing the collision of the expanding supernova remnant with a ring of dense material ejected by the progenitor star 20,000 years before the supernova. The Honeycomb Nebula. The wispy ring just right of centre is the remnant of the supernova.
Credit ESO The expanding ring-shaped remnant of SN 1987A and its interaction with its surroundings, seen in X-ray and visible light. SN 1987A was a supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 51.4 kiloparsecs from Earth, approximately 168,000 light-years,[3] close enough that it was visible to the naked eye. It could be seen from the Southern Hemisphere. Discovery[edit] Progenitor[edit] SN 1987A, one of the brightest stellar explosions detected since the invention of the telescope more than 400 years ago[8] Neutrino emissions[edit] Missing neutron star? Light curve[edit] Homestake experiment. The Homestake experiment (sometimes referred to as the Davis experiment) was an experiment headed by astrophysicists Raymond Davis, Jr. and John N.
Bahcall in the late 1960s. Its purpose was to collect and count neutrinos emitted by nuclear fusion taking place in the Sun. Bahcall did the theoretical calculations and Davis designed the experiment. After Bahcall calculated the rate at which the detector should capture neutrinos, Davis's experiment turned up only one third of this figure. The experiment was the first to successfully detect and count solar neutrinos, and the discrepancy in results essentially created the solar neutrino problem.
The experiment operated continuously from 1970 until 1994. The University of Pennsylvania took it over in 1984. Methodology[edit] The reaction threshold is 0.814 MeV, i.e. the neutrino should have at least this energy to be captured by the chlorine-37 nucleus. Conclusions[edit] See also[edit] References[edit] Raymond Davis Jr.' Coordinates: Liste der Neutrinoexperimente. Neutrinodetektoren (auch Neutrino-Observatorien oder -teleskope) sind Teilchendetektoren speziell für den Nachweis und die Messung von Neutrinos.
Abhängig von der Neutrinoquelle kann man die Neutrinodetektoren in drei Familien einteilen: solare NeutrinodetektorenDetektoren in der Nähe von KernkraftwerkenDetektoren für Neutrinostrahlen Einige wichtige Neutrinodetektoren sind in der folgenden Tabelle aufgeführt. Cowan–Reines neutrino experiment. The Cowan–Reines neutrino experiment was performed by Clyde L. Cowan and Frederick Reines in 1956. This experiment confirmed the existence of the antineutrino—a neutrally charged subatomic particle with very low mass. Background[edit] During the 1910s and 1920s, through the study of electron spectra from the nuclear beta decay, it became apparent that, in addition to an electron, another particle with very small mass and with no electric charge is emitted in the beta-decay but not observed.
The observed electron energy spectrum was continuous. Potential for experiment[edit] Via the inverse beta decay, the predicted electron antineutrino (ν e), should interact with a proton (p) to produce a neutron (n) and positron (e+) – the antimatter counterpart of the electron. ν e + p → n + e+ The positron quickly finds an electron, and they annihilate each other. Most hydrogen atoms bound in water molecules have a single proton for a nucleus. Setup[edit] n + 108Cd → 109mCd → 109Cd + γ Results[edit] Messungen der Neutrinogeschwindigkeit. Gemäß der speziellen Relativitätstheorie muss die Geschwindigkeit von Neutrinos immer geringfügig unter der Lichtgeschwindigkeit liegen, am deutlichsten bei kleiner Energie des Neutrinos. Bisherige Messungen ergeben eine obere Grenze für Abweichungen von 10−9, also ungefähr einem Milliardstel der Lichtgeschwindigkeit.
Das stimmt im Rahmen der Messgenauigkeit mit der Vorhersage der Relativitätstheorie überein. Überblick[Bearbeiten] mit der Neutrinogeschwindigkeit v und der Lichtgeschwindigkeit c. Die Neutrinomasse m wird auf unter 2 eV/c² geschätzt und ist möglicherweise kleiner als 0,2 eV/c². Bisherige Experimente benutzten allerdings Neutrinoenergien von über 10 MeV. Fermilab (1970er)[Bearbeiten] (95 % Konfidenzintervall). Eine Energieabhängigkeit der Neutrinogeschwindigkeit konnte bei dieser Messgenauigkeit ebenfalls nicht festgestellt werden. Supernova 1987A[Bearbeiten] MINOS (2007)[Bearbeiten] Es ergab sich eine frühzeitige Neutrinoankunft von ungefähr 126 ns.
Endresultat[Bearbeiten] Lepton. Das Standardmodell mit den Leptonen in grün Leptonen unterliegen der schwachen Wechselwirkung und der Gravitation. Sofern sie eine elektrische Ladung tragen, wechselwirken sie auch durch die elektromagnetische Wechselwirkung. Alle Leptonen sind Fermionen und besitzen einen Spin ½. Elektron, Myon und Tauon tragen eine negative Elementarladung.
Die Neutrinos sind nicht geladen, unterscheiden sich aber durch ihren Flavour (e, oder ). Für den Fall, dass die Flavour-Eigenzustände nicht den Massen-Eigenzuständen der Neutrinos entsprechen, ist der Flavour keine Erhaltungsgröße mehr. Nachgewiesen zu werden (Neutrinooszillationen). Siehe auch[Bearbeiten] Weblinks[Bearbeiten] The Problem of Mass for Quarks and Leptons - Vortrag (engl.) von Harald Fritzsch am 22. Einzelnachweise[Bearbeiten] Hochspringen ↑ Wilhelm Gemoll: Griechisch-Deutsches Schul- und Handwörterbuch. Bethe-Weizsäcker-Zyklus. Der Bethe-Weizsäcker-Zyklus (auch CNO-Zyklus, CN-Zyklus, Kohlenstoff-Stickstoff-Zyklus) ist eine der beiden Fusionsreaktionen des so genannten Wasserstoffbrennens, durch die Sterne Wasserstoff in Helium umwandeln; die andere ist die Proton-Proton-Reaktion. Der Zyklus wurde zwischen 1937 und 1939 von den Physikern Hans Bethe und Carl Friedrich von Weizsäcker entdeckt. Die Namen CN- beziehungsweise CNO-Zyklus leiten sich von den an der Reaktion beteiligten Elementen Kohlenstoff (C), Stickstoff (N) und Sauerstoff (O) ab.
Während die Proton-Proton-Reaktion eine wichtigere Rolle bei Sternen mit Größen bis zur Masse der Sonne spielt, zeigen theoretische Modelle, dass der Bethe-Weizsäcker-Zyklus vermutlich die vorherrschende Energiequelle in schwereren Sternen darstellt. Die Sonne selbst erzeugt nur 1,6 % ihrer Energie durch den Bethe-Weizsäcker-Zyklus. Der Bethe-Weizsäcker-Zyklus läuft erst bei Temperaturen über 14 Millionen Kelvin ab und ist ab 30 Millionen Kelvin vorherrschend. C. ICARUS. ICARUS ( englisch Imaging Cosmic And Rare Underground Signals ) ist ein physikalisches Experiment zur Untersuchung von Neutrinos . Es befindet sich in den Laboratori Nazionali del Gran Sasso (LNGS). Das Experiment ist die Weiterentwicklung eines von Carlo Rubbia 1977 vorgeschlagenen Teilchendetektortyps . [1] Es handelt sich dabei um eine Liquid Argon Time Projection Chamber (LAr-TPC).
Sie soll die Vorteile einer Blasenkammer mit einem elektronischen Ausleseverfahren verbinden. Im Zuge des ICARUS-Programms wurden mehrere Detektoren gebaut. 2010 wurde der ICARUS-T600-Detektor im LNGS mit 760 Tonnen Flüssigargon als größter Detektor dieser Art in Betrieb genommen. Die CNGS-Messungen wurden zusätzlich bedeutsam, als die OPERA-Gruppe im September und November 2011 die Messung von angeblich überlichtschnellen Neutrinos bekanntgab. Weblinks [ Bearbeiten ] HomePage Einzelnachweise [ Bearbeiten ] ↑ Rubbia, C.: The liquid-Argon time projection chamber: a new concept for neutrino detector . Proton–proton chain reaction. The proton–proton chain reaction dominates in stars the size of the Sun or smaller.
The proton–proton chain reaction is one of several fusion reactions by which stars convert hydrogen to helium , the primary alternative being the CNO cycle . The proton–proton chain dominates in stars the size of the Sun or smaller. In general, proton–proton fusion can occur only if the temperature (i.e. kinetic energy ) of the protons is high enough to overcome their mutual electrostatic or Coulomb repulsion . [ 1 ] In the Sun, deuterium -producing events are so rare ( diprotons , the much more common result of nuclear reactions within the star, immediately decay back into two protons) that a complete conversion of the star's hydrogen would take more than 10 10 (ten billion) years at the prevailing conditions of its core. [ 2 ] The fact that the Sun is still shining is due to the slow nature of this reaction; if it went more quickly, the Sun would have exhausted its hydrogen long ago. [ edit ]
Lepton. A lepton is an elementary, spin-1⁄2 particle that does not undergo strong interactions, but is subject to the Pauli exclusion principle.[1] The best known of all leptons is the electron, which governs nearly all of chemistry as it is found in atoms and is directly tied to all chemical properties. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos).
Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. The first charged lepton, the electron, was theorized in the mid-19th century by several scientists[3][4][5] and was discovered in 1897 by J. J. Leptons are an important part of the Standard Model. Etymology[edit] Following a suggestion of Prof. The etymology incorrectly implies that all the leptons are of small mass. History[edit] Properties[edit] Mass[edit] Quasiparticle. These fictitious particles are typically called "quasiparticles" if they are related to fermions (like electrons and holes), and called "collective excitations" if they are related to bosons (like phonons and plasmons),[1] although the precise distinction is not universally agreed.[2] Quasiparticles are most important in condensed matter physics, as it is one of the few known ways of simplifying the quantum mechanical many-body problem.
Overview[edit] General introduction[edit] Solids are made of only three kinds of particles: Electrons, protons, and neutrons. Quasiparticles are none of these; instead they are an emergent phenomenon that occurs inside the solid. Therefore, while it is quite possible to have a single particle (electron or proton or neutron) floating in space, a quasiparticle can instead only exist inside the solid.
In summary, quasiparticles are a mathematical tool for simplifying the description of solids. Relation to many-body quantum mechanics[edit] History[edit]