The neutrinos and antineutrinos are tiny, almost massless particles that are virtually impossible to detect. The reverse process, whereby a proton becomes a neutron through the emission of a positron and a neutrino, is the source of beta-positive radiation. The alternative to correct an excess of one type of nucleons – the direct expulsion of a proton or neutron from the nucleus – costs generally energy and occurs only for very unstable nuclei produced in reactors with a large excess of neutrons.īeta-minus radiation, the emission of an electron and an anti-neutrino, occurs when a neutron transforms into a proton. The electron is expelled together with a kind of neutral positron – an antineutrino – while a positron is expelled with a neutrino, the neutral counterpart of the electron.īeta decays are observed in Nature, when the process releases energy, which is the case for beta emitters. This transformation does not change the total number of nucleons, but is accompanied by the emission of an electron (or a positron) to compensate the change of electric charge. At the time of the decay, two other particles are created: an electron and an antineutrino which is able to pass undetected.Īt the origin of this type of radiation is a force within the nucleus capable of transforming one type of nucleon into another (a proton into a neutron, or vice versa): the so-called ‘ weak‘ forces. To even the balance, one of these neutrons transforms into a proton (shown in red) to form a stable nucleus of nickel 60 with 28 protons (one more than before) and 32 neutrons (one fewer than before). Examples of a few of the projects focused on this phenomenon are the Majorana Demonstrator and EXO in the United States and CUORE and GERDA in Italy.A cobalt 60 nucleus, containing 33 neutrons and 27 protons, has an excess of 6 neutrons – shown in blue. Some of the more common elements used for these experiments include germanium, cadmium, and xenon. Even the normal activity of atoms bouncing around can cause problems, so experiments often operate at temperatures colder than outer space. This method is difficult because any amount of background radiation coming from the equipment, atmosphere, or nearby surroundings can create so much noise and confusion that the decay might go unnoticed. Most experiments to study neutrinoless double beta decay use a large amount of very pure material and look for electrons carrying away a signature amount of energy. It’s only possible if the antineutrino and neutrino are actually the same, a property that would make them so-called “ Majorana particles.” Many scientists believe that neutrinos are indeed Majorana particles, and a number of incredibly precise experiments are looking for this neutrinoless double beta decay. In this reaction, two neutrons would become two protons, a virtual neutrino exchange would cause the antineutrino emitted by one beta decay to be reabsorbed in the second decay, and electrons would carry away all the energy-but this requires neutrinos to have a special property. This is the aptly named double beta decay.Īn even rarer process, if it exists, would be neutrinoless double beta decay. On occasion, two beta decays happen almost simultaneously, releasing two electrons and two electron antineutrinos. The laws of physics require that a few different properties be conserved, so the process also releases an electron and an electron antineutrino. A down quark within the neutron transforms into an up quark, changing the neutron into a proton (and changing the atomic element as a result). Protons and neutrons consist of fundamental particles called quarks. One type (the kind that happens in nuclear reactors) is when a neutron turns into a proton. Let’s look at a process called beta decay. This reaction can happen in a neutron within an atom or a free-floating neutron. In a beta decay, a neutron (made of one up quark and two down quarks) can transform into a proton (made of two up quarks and one down quark), an electron, and an electron antineutrino.
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