13.2.3
When an unstable substance undergoes alpha-decay, there will be alpha paticle emission. If was discovered that the alpha particles given off all had different kinetic energies HOWEVER they were only ever given off in those discrete, or specific, kinetic energies. For example, a substance would emit alpha particles with energies of say, 2,3,4 and 4 MeV. The alpha particles given off would only ever be emitted with those respected kinetic energies, and never anything different or anything in between. This proves that there are discrete energy levels in not only electron orbitals, but also in the nucleus of the atom itself.
Another method of proving nuclear eenrgy levels is from looking at the gamma photon emission of the daughter nucleus. What this means is that when the parent nucleus undergoes alpha decay and emits alpha particles of dsicrete kinetic energies, some will have maximum amount of kinetic energy possible, hence leaving the daughter nucleus in its ground state. However there will also be some that are emitted with not the maximum possible amount of kinetic energy, hence leaving the daughter nucleus in an excited state. As a result of this daughter nucleus having excess energy, the nucleus will emit gamma radiation of a discrete frequency. The energy associated to the photon(s) emitted will be equal to hf.
13.2.4
Whenever beta or beta-plus decay occurred, it was found that the kinetic energies of the electron or the positron were not equal to the mass defect from the neutron changing into a proton or a proton changing into a neutron. As a result of this unexplained 'lost' energy, there must have been another particle (in addition to the electron/positron) which was emitted during beta/beta+ decay to compensate for the lack of energy. It was then proposed that this particle would have to have almost zero mass and a neutral charge. This particle was named the neutrino.
During beta decay an electron and an anti-neutrino is emitted from the nucleus. In beta+ decay, a positron and a neutrino is emitted. There are three 'flavours' of neutrinos: the electron neutrino, muon neutrino and the tauon neutrino (and there respected anti-neutrinos). This explained why during the detection process, only a third of the anticipated neutrinos were detected. Only the electron neutrinos were being detected whilst the two others remained undetected.
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