Fermi Theory of Beta Decay

费米β衰变理论

In 1930, Wolfgang Pauli postulated the existence of the neutrino to explain the continuous distribution of energy of the electrons emitted in beta decay. Only with the emission of a third particle could momentum and energy be conserved. By 1934, Enrico Fermi had developed a theory of beta decay to include the neutrino, presumed to be massless as well as chargeless.

1930年，沃尔夫冈·泡利提出中微子的存在，以解释β衰变中发射的电子能量的连续分布。只有在释放出第三个粒子的情况下，动量和能量才能守恒。到1934年，恩里科·费米已发展出一个包含中微子的β衰变理论，中微子被认为既无质量又不带电。

Treating the beta decay as a transition that depended upon the strength of coupling between the initial and final states, Fermi developed a relationship which is now referred to as Fermi's Golden Rule:

将β衰变视为初始态与最终态之间耦合强度决定的转变过程，费米提出了一个关系式，现在被称为费米黄金规则：

Straightforward in concept, Fermi's Golden Rule says that the transition rate is proportional to the strength of the coupling between the initial and final states factored by the density of final states available to the system. But the nature of the interaction which led to beta decay was unknown in Fermi's time (the weak interaction). It took some 20 years of work (Krane) to work out a detailed model which fit the observations. The nature of that model in terms of the distribution of electron momentum p is summarized in the relationship below.

概念上很直接，费米的黄金规则指出，跃迁率与初始态和终态之间的耦合强度成正比，并且该强度被终态态密度所除。但当时（弱相互作用）导致β衰变的相互作用性质尚不清楚。经过约20年的研究（克兰），才建立出一个详细的模型，该模型符合观测结果。该模型在电子动量p的分布方面的性质总结在下式中。