Neutron continued interaction with nucleus

Fig. 5.6. Path of s and r processes across the Z, N) plane. Everything begins with iron. The s process follows roughly along the valley of statrility, flowing like a river along the banks it defines. It ends with the a decay of bismuth-209. The r process takes matter far out of the valley on the neutron-rich side, whilst the weak interaction brings it back to the fold. In this case neutron capture continues until the nucleus undergoes fission. The climb to neutron-rich summits is indeed vertiginous.

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 nuclear processes of most interest to the nuclear industry are radioactive decay and the transmutation of nuclides. Whereas chemical processes relate to the interactions of orbital electrons of the atom, nuclear processes relate to interactions of neutrons, charged particles, and nuclides with the neutrons and protons in the nucleus of the atom. As noted above, there are now known about 3000 nuclides and isomers and only 287 of these are naturally occurring. More continue to be found. As Mendeleev invented the chart of the chemical elements, Emilio Segre invented the chart of the nuclides to give order to the nuclear properties and processes. 

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