Beta decay spectrum

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. 

Another kind of particle and another kind of interaction were discovered from a detailed study of beta radioactivity in which electrons with a continuous spectrum of energies are emitted by an unstable nucleus. The corresponding interactions could be viewed as being due to the virtual transmutation of a neutron into a proton, an electron, and a new neutral particle of vanishing mass called the neutrino. The theory provided such a successful systematization of beta decay rate data for several nuclei that the existence of the neutrino was well established more than 20 years before its experimental discovery. The beta decay interaction was very weak even compared to the electron-photon interaction. 

The fluctuations in neutron peak intensities arise from the Porter-Thomas distributed beta decay widths to levels in the NE nuclide. In the simplest case only a single state in the GC nuclide can be fed and only one neutron partial wave is significant. The observed levels will be a subset of levels in the NE nuclide and will be distributed in energy following a Wigner distribution. In a typical GC nuclide, however, there will be a number of accessible final states and the delayed neutron spectrum will be a superposition of transitions from several parts of the NE nuclide level structure. 

The division between electrons and betas is necessary (although beta particles are electrons) because an electron beam consists of monoenergetic electrons a beam of beta particles consists of electrons emitted by the beta decay of a nucleus. Therefore, as explained in Chap. 3, these particles have an energy spectrum with a maximum energy and an average energy... 

The beta decay probabilities calculated using the exact wavefunctions are shown in Fig. 74 as a function of Vf.. The superallowed decay of Ne is not a sharp function of the interaction potential, since there is no change of supermultiplet, but the 0 decays give an estimate of which agrees fairly well with that 0 —obtained from the level spectrum. 

No levels of the proton-unstable nucleus are known. levels are obtained from the (dp), (den) and (hol) reactions. The beta decay of to the 0 ground state is first forbidden, but transitions to the 7.12 and 6.14 MeV negative parity states are allowed, and the subsequent gamma radiation has been detected. The spin of is therefore probably 2". The isotopic spin allowed transition between the 7.12 and 6.14 MeV levels was not observed and the difference in intensity between the beta-spectrum components and the subsequent radiations is attributed to experimental uncertainties in the measurement of the former. 

Figure 4 The energy spectrum of antineutrinos produced by the fission of Pusagand U235 multipiied by the inverse beta decay cross section. The interaction threshoid is 1.8 MeV.

In thorium fuel, TJ is produced in-reactor through neutron capture in and subsequent beta-decay of h and Pa. The concentration of U in the spent fuel is about five-times higher than that of Pu in spent natural uranium UO2 fuel. This isotope of uranium is a very valuable fissile material because of the many neutrons produced per neutron absorbed (g) in a thermal neutron spectrum. 

The beta decay of in an iodine compound often leads to a xenon compound with the same ligands. The Mossbauer spectrum of the gamma radiation emitted from the Xe nuclei so formed shows hyperfine structure. This is due to the nuclear electric quadrupole moment eQ of the excited Xe nucleus, which results in a doublet absorption spectrum if the electric field gradient eq —d VIdz ) does not vanish. The observed quadrupole splitting equals e qQ 2 if the asymmetry parameter of the electric field gradient is negligible. (See Chapter 2.)... 

In terms of what is measured or observed, there are (1) portions of the electromagnetic spectrum gamma-ray, cosmic ray, x-ray, ultraviolet, infrared, far-infrared, microwave, and radiowave instruments (2) regions pertaining to the energies of particles beta ray (electrons), protons, neutrons, and mass associated instruments and (3) instruments dealing with other spectra such as radioactive decay and Mossbauer effects. 

The activities of some isotopes, in particular °Sr- °Y, can also be detected by liquid-crystal spectrometry with the use of the Cherenkov phenomenon [10, 11]. The Cherenkov effect is used to determine beta isotopes emitting particles whose iiniax IS above 500 keV [12]. The main advantage of beta activity determination by the Cherenkov effect is the use of analytical preparation used for another chemical analysis (e.g. calculation of recovery). Moreover, the addition of low energy beta or alpha radiation does not disturb the measurement, thereby lowering the cost of analysis. The weakness of this method is the decreased recovery registration and the decline in information about the realistic appearance of the beta spectrum [13]. The determination of beta isotopes in environmental samples is very difficult and requires their chemical isolation. The type of sample and the time of chemical analysis determine the choice of analytical method. Also, the time between contamination and sample collection is important procedures used for samples recently contaminated are different to those used for old samples in which the decay of short-lived radionuclides has aheady taken place [1, 5]. 

Beta particles are emitted when a neutron is converted to a proton plus an electron and the electron is lost. Unlike the discrete energy emissions from the decay of alpha particles, beta particles are emitted along a spectrum of energies, because energies are shared between positive and negative electrons. Positrons are emitted when a proton becomes a neutron and decays by beta emission or an electron is captured. These are competing processes, and both occur with about the same frequency (Harley, 2001, 2008). 

In contrast to alpha emission, beta emission is characterized by production of particles with a continuous spectrum of energies ranging from nearly zero to some maximum that is characteristic of each decay process. The jS particle is not nearly as effective as the alpha particle in producing ion pairs in matte r because of its small mass (about /7(XK) that of an alpha particle), At the same time, its penetrating power is substantially greater than that of the alpha particle. Beta-particle energies are frequently related to the thickness of an absorber, ordinarily aluminum, required to stop the particle. 

The nuclei of mass 39 are analogous to 0 in that single particle (actually hole) levels are expected to occur in Ca. There is no evidence on this point. The decay to appears from the positron spectrum end-point to be governed by the Coulomb energy, and in this case the T =— nucleus is again stable. A also decays, by a forbidden transition, to the 3/g+ ground state of Analysis of the shape of the beta spectrum classifies the transition as Zl/ = 2, yes, so that... 

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