Скачать или смотреть 27.3 Nuclear Decay Processes and Energy of Nuclear Reactions | General Physics

Chad provides a lesson on the various spontaneous Processes of Nuclear Decay and on the Energy of Nuclear Reactions. The spontaneous processes of nuclear decay include alpha decay, beta decay (beta emission and positron emission), and gamma decay. In alpha decay (aka alpha emission), an alpha particle is emitted which lowers the atomic number by 2 and the mass number by 4. Alpha decay is most common among heavier nuclei. Two forms of beta decay are discussed: beta emission and positron emission. In beta emission a beta particle (i.e. an electron) is emitted from the nucleus along with an antineutrino. The net result is the conversion of a neutron to a proton which is reflected as an increase in the atomic number by 1 with no change in the mass number. In positron emission a positron (the antiparticle of an electron--effectively a positively charged electron) is emitted from the nucleus along with a neutrino. The net result is the conversion of a proton to a neutron which is reflected as a decrease in the atomic number by 1 with no change in the mass number. Gamma decay (aka gamma emission) is simply the emission of a gamma ray which is just a very high energy photon. The overall identity of the nucleus is unchanged. Gamma emission typically accompanies one of the other decay processes that leaves a nucleus in a high energy state.
In a nuclear reaction, there is a conversion between mass and energy (E=mc^2) and this difference in energy equivalence between the reactants and products is called the Q-value. Exothermic reactions release energy and have positive Q-values, while endothermic reactions consume energy and have negative Q-values. For an endothermic nuclear reaction to occur, one of reactant particles must be given some minimum amount of kinetic energy for the reaction to proceed. It is also demonstrated how to calculate this minimum kinetic energy.

00:00 Lesson Introduction
00:52 Alpha Decay
03:34 Beta Decay (Beta Emission and Positron Emission)
11:23 Gamma Decay
14:11 Energy of Nuclear Reactions and Q-value

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