Beta particle energy spectrum

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. 

Figure 8.6. Example of quenching in a beta-particle energy deposition spectrum in an LS counter.

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. 

In this experiment, tritiated water is purified by simple distillation, and the tritium beta particles in the condensate are measured with a liquid scintillation (LS) counter. Such distillation also can collect tritiated water samples from solids. Tritium in other forms must be processed before it can be counted like tritium in water for example, tritiated hydrogen gas and tritiated organic substances can be oxidized to form water. Additional separations may be needed if the liquid or solid sample contains radioactive gases or volatile substances other than tritium that may be collected with the distilled tritiated water. Such radioactive impurities can be identified in the data output from the LS counter of an energy spectrum that differs from that of pure tritium, or of counts in energy regions where tritium counts are not found. 

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). 

Beta particles are emitted in the form of a spectrum with a characteristic maximum energy and average energy again, particles may be emitted with different energies each with their own characteristic probability, for example ... 

Beta particles have a continuous energy spectrum extending from zero energy up to maximum kinetic energy (see Sec. 3.7.3). If the transmission experiment shown in Fig. 4.5 is repeated with an incident beam of jS particles, the result will look as shown in Fig. 4.11. The number of betas N(t) transmitted through a thickness t is very closely represented by... 

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 energy spectrum of a beta-particle group takes the form of a continuum that has different shapes for different radionuclides three are shown in Fig. 2.5. Because of the energy distribution of beta particles, the relationships observed for the interaction of beta particles with matter are not as simple as those of alpha particles. 

Older LS counter systems (see Section 8.3.2) have three channels for distinguishing energies new ones have full energy spectrometers. These are directly applicable for distinguishing alpha particles by energy. Because beta particles are emitted as a spectrum from zero to maximum energy, and the spectra have various shapes, identification of beta-particle emitters by energy is less feasible. 

The energy spectrum presented by the LS system does not exactly reflect the beta-particle spectrum because some energy is not deposited or is lost in... 

As an example, the information in Table 8.6 summarizes the data collected for a C standard (134,900 dpm) in six energy regions of the beta-particle spectrum. The table also includes the data from a simulated unknown sample with °Sr and in secular equilibrium with a total beta-particle-activity of 1037 dpm. 

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