Electron antineutrino

Figure 2a, b. Antineutrino number distribution function for the 1.64 Hq core evolved with the soft EOS. The maximum is normalized to unity, as only the shape of the curve is being considered. Also shown is the shape of the expected positron number spectrum that would be produced by electron antineutrino capture on protons taking into account detector characterestics. 

Because the values of BJZ) are generally small relative to the masses of the nuclei and electrons, we shall neglect this factor in most calculations. Let us make a few calculations to illustrate the use of masses in describing nuclear phenomena. Consider the 0 decay of 14C, that is, 14C -> 14N+ + (3 + ve + energy. Neglecting the mass of the electron antineutrino, thought to be a few electron volts or less, we have... 

The third force is the "weak nuclear" or "Fermi"4 force (1934), which stabilizes many radioactive particles and the free neutron it explains "beta decay" and positron emission (e.g., the free neutron decays within a half-life of 13 minutes into a proton, an electron, and an electron antineutrino). The weak force has a very narrow range. 

The decay of a free neutron qH1 electron antineutrino into a proton xpl, an electron e, and an... 

C-14 dating was discovered by Libby11 and co-worker [2], The cosmic ray flux has been fairly constant over prehistoric and current time and provides a small but almost constant supply of 6C14, at a rate averaged over the whole atmosphere of about 2.2 atoms cm-2 s 1. The radioactive 6C14 will bind to oxygen in the atmosphere to form radioactive carbon dioxide, but will decay, with a half-life fi/2 = 5730 years, by emitting an electron (or "fj ray") and an electron antineutrino ... 

Electron neutrino V e OtollO- stable 0 Electron antineutrino, i,. 

Nuclides with an excess of neutrons experience P decay. In the nucleus a neutron is converted into a proton, an electron and an electron antineutrino, as indicated in Table 5.1. The atomic number increases by one unit, whereas the mass number does not change (second displacement law of Soddy and Fajans). The energy of the decay process can again be calculated by comparison of the masses according to Einstein ... 

The bar over the neutrino symbol in this equation represents an antineutrino in its reaction with a gamma ray to produce an antiproton. Similarly, an antielectron is formed in the reaction between a gamma ray and an electron antineutrino ... 

Pauli proposed that two particles were emitted, and Fermi called the second one a neutrino, V. The complete process therefore is n — p -H e 9. Owing to the low probabiHty of its interacting with other particles, the neutrino was not observed until 1959. Before the j3 -decay takes place there are no free leptons, so the conservation of leptons requires that there be a net of 2ero leptons afterward. Therefore, the associated neutrino is designated an antineutrino, 9-, that is, the emitted electron (lepton) and antineutrino (antilepton) cancel and give a net of 2ero leptons. 

In the last decade, neutrino experiments have demonstrated that neutrinos are massive particles which may oscillate among three autostates. Such experiments [77-82] have evidenced the mass difference between the autostates, but not the neutrino mass scale value. The only way to determine the neutrino mass is the knowledge of the shape of the end point of energy spectrum in beta decays. In the hypothesis of the Majorana neutrino (neutrino coincides with antineutrino and its rest mass is different from zero), the measure of the decay half-life in the neutrinoless double-beta decay (DBD) would be necessary. A number of recent theoretical interpretations of neutrino oscillation experiments data imply that the effective Majorana mass of the electron neutrino (as measured in neutrinoless DBD) could be in the range 0.01 eV to the present bounds. 

A nucleus (A Z) decays with the emission of two electrons (e ) and two antineutrinos (ve) following the equation ... 

During most of the first 0.1 second after the Big Bang (ABB), the relativistic particles are photons, electrons, positrons and Nv species of neutrinos and antineutrinos Nv is expected to be 3, from ve, vfl and vr. There is a sprinkling of non-relativistic protons and neutrons which make a completely negligible contribution to the energy density. The temperature is then given by... 

This is a process characteristic of nucleides with high n p ratios, and involving the loss of an electron from the nucleus, which is usually, but not invariably accompanied by the emission of y-photons. A detailed energy balance reveals that the simple picture cannot account for all the energy lost by the nucleus in the decay and the emission of an additional particle - the antineutrino, v is postulated to account for this. The general equation for a negatron emission is... 

The merger remnant emits neutrinos in copious amounts. The total neutrino luminosities are typically around 2 1053 ergs/s with electron-type antineutrinos carrying away the bulk of the energy. Typical neutrino energies... 

Beta-minus Beta-minus decay essentially mirrors beta-plus decay. A neutron converts into a proton, emitting an electron and an anftneutrino (which has the same symbol as a neutrino except for the line on top). Particle and antiparticle pairs such as neutrinos and antineutrinos are a complicated physics topic, so we ll keep it basic here by saying that a neutrino and an antineutrino would annihilate one another if they ever touched, but they re otherwise very similar. Again, the mass number remains the same after decay because the number of nucleons remains the same. However, the atomic number increases by 1 because the number of protons increases by 1 ... 

Is the neutron as we understand it today really a combination of a proton and electron as Rutherford envisioned it This is a philosophically interesting question. When neutrons decay, they produce a proton and an electron (and an antineutrino as well) however, these particles are not understood to have a real existence within an intact neutron. Indeed, the constituent parts of neutrons (and protons for that matter) are understood to be quarks. The phenomenon of neutron decay is explained by a transformation of one of its constituent quarks, turning the neutron into a proton the energy difference between the neutron and proton gives rise to the electron and antineutrino. 

Beta particles consist of electrons traveling at very high speeds. These electrons do not come from the electron shield of the atoms, but from the nucleus itself. In the (f-decay process, a neutron in the nucleus is transformed into a proton, an electron, and an antineutrino, P. For example, the nucleus of suffers the decay gC — + e+qP. In this equation, the electron e is called a [1 particle. 

There are a number of other interesting limits to be drawn on neutrino properties by somewhat more sophisticated use of the supernova dynamics. Putting another neutrino-antineutrino pair [30], i.e., another two species, into any calculation of the neutron star cooling would probably accelerate this process unacceptably. Further, one can place an upper limit [5] of 45 eV on the mass of any species mixing with the electron neutrino, else no supernova mechanism would succeed, delayed or prompt. 

These reactions, called inverse (3 decay, were obtained by adding the antiparticle of the electron in the normal (3 decay equation to both sides of the reaction. When we did this we also canceled (or annihilated) the antiparticle/particle pair. Notice that other neutrino-induced reactions such as ve + n —> p+ + e do not conserve lepton number because an antilepton, ve, is converted into a lepton, e. Proving that this reaction does not take place, for example, would show that there is a difference between neutrinos and antineutrinos. One difficulty with studying these reactions is that the cross sections are extremely small, of order 10-19 bams, compared to typical nuclear reaction cross sections, of order 1 barn (10—24 cm2). 

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