Beta decay neutrino verification#
Beta decay neutrino plus#

Beta decay neutrino plus#

One example is 40K, which undergoes all three types of beta decay (beta minus, beta plus and electron capture) with half life of 1.277×10 9 years. In nature, most isotopes are beta stable, but a few exceptions exist with half-lives so long that they have not had enough time to decay since the moment of their nucleosynthesis. It should be noted, that a beta-stable nucleus may undergo other kinds of radioactive decay ( alpha decay, for example). Among them, several nuclides (at least one) are beta stable, because they present local minima of the mass excess: if such a nucleus has ( A, Z) numbers, the neighbour nuclei ( A, Z−1) and ( A, Z+1) have higher mass excess and can beta decay into ( A, Z), but not vice versa. Thus the set of all nuclides with the same A can be introduced these isobaric nuclides may turn into each other via beta decay.

For example:īeta decay does not change the number of nucleons A in the nucleus but changes only its charge Z. If the proton and neutron are part of an atomic nucleus, these decay processes transmute one chemical element into another. In all the cases where β + decay is allowed energetically (and the proton is a part of a nucleus with electron shells), it is accompanied by the electron capture process, when an atomic electron is captured by a nucleus with the emission of a neutrino:īut if the energy difference between initial and final states is low (less than 2 m e c 2), then β + decay is not energetically possible, and electron capture is the sole decay mode. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles. Beta plus decay can only happen inside nuclei when the absolute value of the binding energy of the daughter nucleus is higher than that of the mother nucleus. So, unlike beta minus decay, beta plus decay cannot occur in isolation, because it requires energy, the mass of the neutron being greater than the mass of the proton. In β + decay, energy is used to convert a proton into a neutron, a positron ( e + ) and a neutrino ( ν e): In β − decay, the weak interaction converts a neutron ( n 0) into a proton ( p +) while emitting an electron ( e −) and an anti-neutrino ( ):Īt the fundamental level (as depicted in the Feynman diagram below), this is due to the conversion of a down quark to an up quark by emission of a W - boson the W - boson subsequently decays into an electron and an anti-neutrino. In the case of electron emission, it is referred to as 'beta minus' (β −), while in the case of a positron emission as 'beta plus' (β +). If neutrinoless DBD exists it will be an extremely rare decay and so to observe it will require a large source mass (of enriched isotope), a highly efficient detector with good energy resolution and very low (nearly zero) backgrounds.In nuclear physics, beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. Spectrum of summed electron-energies, relative to the Q value, for double beta decay (ββ2ν) and for neutrinoless double beta decay (ββ0ν). The nuclear recoil energy is negligible and hence the sum of the electron energies is just the decay Q value smeared by the detector resolution (see fig.2).įigure 2. Neutrinoless DBD can be recognized by its electron-sum energy spectrum. The Majorana hypothesis is currently favoured in GUT (Grand Unified Theories) and supersymmetric theories. This reabsorption requires that the neutrino is its own antiparticle (a Majorana fermion) and is not in a pure helicity state (i.e. In this case the neutrino is reabsorbed by the intermediate nucleus.

If lepton-number is violated neutrinoless DBD (fig.1b) may occur. However, lepton-number is not associated with a gauge symmetry and hence need not be universally conserved. 76Ge → 76Se + 2e - + 2 neutrinos with a measured half life of ~10 21 years). This lepton-number conserving process, 2-neutrino DBD decay (fig.1a), has been observed in several nuclei (e.g. If lepton number is also to be conserved two antineutrinos must be emitted as well. To conserve charge two electrons must be emitted.

Beta decay neutrino verification#

In addition, DBD experiments offer the possibility of determination of the absolute neutrino mass scale and verification of the mass hierarchy of neutrinos (electron-neutrino, muon-neutrino, tau-neutrino).ĭBD is a second-order weak process in which two neutrons inside a nucleus spontaneously transform into two protons. A consequence of this new, beyond the Standard Model physics is renewed interest in DBD experiments which provide the best way to determine the fundamental nature of the neutrino (Dirac or Majorana). The observation of neutrino oscillations has demonstrated that neutrinos have mass.